a brief look at clutches


Staff member


stock replacement












http://www.youtube.com/watch?v=6BaECAba ... re=channel


http://www.circletrack.com/drivetrainte ... ewall.html

http://www.usaperform.com/clutches-bell ... c-468.html

http://www.youtube.com/watch?v=6BaECAba ... re=related

http://www.enginebuildermag.com/Article ... ntrol.aspx


http://www.ramclutches.com/Products/str ... #Powergrip


http://www.dwclutch.com/D&W/D&W%20Clutc ... de%208.pdf




http://www.hotrod.com/techarticles/driv ... index.html


http://www.vetteweb.com/tech/vemp_0910_ ... index.html


http://www.haysclutches.com/ProductsLis ... election=3

http://www.circletrack.com/drivetrainte ... index.html

http://www.circletrack.com/howto/78378_ ... index.html


http://www.haysclutches.com/pdf/Perform ... h_Kits.pdf








your local area is sure to have a decent clutch shop that can sell you a nice heavy duty clutch and pressure plate assembly at a reasonable price, especially if you know exactly what to ask for, get friendly with the guys, you'll be seeing them more than once, but be aware they generally won,t want to assemble a 3600-3800lb clamp load custom clutch unless you assure them its only going to be used for racing and youve fully realized the huge increase in petal pressure required to use it. theres always trade offs, but a good 11" borg and beck clutch set up with heavier springs on a 35-40 lb steel billet flywheel can take a great deal of abuse, on a serious engine and not cost you nearly what some of the more trick, newer versions would cost.
input shaft is the SPLINE shaft the clutch disk rides on not the smooth outer collar the throw-out bearing rides on, that 1.375 throw out bearing is most likely correct, the SPLINE shafts come in different tooth counts if you count those and order the matched disc its most likely going to fit
discs come in 10 spline and 26 spline count types and 10.4" and 11" diam. for most chevy clutches, naturally the spline count must match the input shaft and the diam. must match the pressure plate, BRING OLD PARTS TO THE CLUTCH REBUILDER, OR AUTO PARTS STORE TO TEST MATCH AND COMPARE WITH THE NEW PARTS
keep in mind the less a clutch slips the less heat and wear it has, and in most cases the longer it lasts but to get less slippage usually requires a higher clamping pressure resulting in a stiffer petal, and a more pronounce GRABBING or smooth power application,as it seats.
now learning how to shift helps a great deal, and not riding the clutch helps, but everything a compromise in some area, and doubling the clutch surface with a dual disc design has advantages in some applications.
replacing a clutch in a car brings back memories, I remember installing a clutch disk withe the wrong side facing the pressure plate when I was about 19 years old and effectively had to do the whole clutch replacement job a second time because of that stupid move, but you can be 100% sure I never did that again , co its part of paying your dues in the hobby, a learning experience
mportance of Pressure Plate
The pressure plate is an integral factor in the function of an automobile’s manual transmission. The pressure plate pushes the clutch disc, sometimes called the clutch plate, against the constantly spinning engine flywheel. The clutch disc, therefore, is either stationary or rotating at the same speed as the flywheel. Friction material, similar to that found on brake pads and brake drums, causes the clutch disc to spin at the same speed as the engine flywheel. It is this friction between clutch disc and flywheel that allows the engine torque to drive the wheels.
Pressure plates are, as the name implies, round, metallic devices containing springs and fingers, or levers, and controlled by the release fork connected to the shifter. All of the clutch components are enclosed in the bell housing of the transmission, between the rear of the engine and the front of the gearboxWhen the driver steps on the clutch pedal, a number of springs in the pressure plate are compressed by multiple — most often three — fingers. This compression of the spring(s) pulls the pressure plate and the clutch disc away from the flywheel and thus prevents the clutch disc from rotating. When the clutch disc is stationary, the driver can shift into the proper gear and release the clutch pedal. When the pedal is let up, the fingers in the pressure plate release their grip and the spring(s) expand to push the pressure plate into the clutch disc, thereby engaging the flywheel. This release process is often called the “clamp load”.
There are three major types of pressure plates: (1) The Long style which contains nine coil springs for pressure against the flywheel and three thin fingers for release. The Long style plate is used mainly for drag racing. (2) The Borg & Beck style also contains nine coil springs and three fingers. The fingers are wider, however, and the Borg & Beck has the more robust materials and design necessary for street driving. (3) The diaphragm pressure plate is best suited for street use and is, therefore, the most common type found on later-model automobiles. It contains a single Bellville-style spring that applies a more even load from clutch plate to flywheel. Because the single-spring diaphragm is more effective “over-center”, there is also less effort needed by the driver to hold the clutch pedal in the depressed position at a stop.








standard diaphragm replacement clutch



Diaphragm pressure plates work well for street/strip applications, featuring maximum clamp load with minimum pedal effort, but have a bad habit of sticking to the floor in the cheaper designs if shifted at high rpms
GM Diaphragm Pressure Plates
If you need a clutch for your everyday driver, this is the clutch for you. RAM clutch sets are the first choice of professional installers because each set contains the correct, top quality replacement parts to ensure proper fit and operation in your vehicle. Every RAM premium clutch set is backed by our five year/50,000 mile limited warranty.


borg and beck style


you can have stiffer springs installed in a clutch pressure plate that can significantly increase the clamp loads, this tends to increase petal effort but also increases clutch life in most cases
most of these BORG & BECK clutch pressure plate's don,t use the stiff springs or for that matter springs in all locations in that pressure plate.



This type of clutch will increase the pedal effort in order to achieve the extra holding power, and may require strengthening of your clutch linkage components for proper operation. Roller, or centrifugal assist models are available for non-shifting applications such as clutch less transmissions, or where shifting is done below 6000 RPM.

long style
look close AND notice the center location in each group of three coil springs is missing on this pressure plate


The Long Style is the preferred pressure plate for true competition clutch systems. These units provide a combination of static and centrifugal pressure. This characteristic allows setting up the clutch to suit the car and track conditions. Static pressure is provided by coil springs and remains constant throughout the RPM range of the motor. Additional pressure is provided by centrifugal force acting on the levers which impart this force to the pressure ring of the clutch. Centrifugal pressure is RPM sensitive, meaning the force increases as the engine RPM increases. Long Style clutches are available with fixed static and centrifugal pressure or with adjustable pressures to allow precise clutch tuning. Long Style clutches feature explosion resistant pressure rings, chrome vanadium springs for long life without loss of pressure, welded spring guide cups in a heavy duty cover, and all new heavy duty hardware. RAM can build Long Style clutches in any pressure range and with or without counterweight levers for non-shifting applications such as Lenco or other clutch less transmissions.
some pressure plate designs have counter weights on pivots to increase pressure holding the disc against the flywheel, as the rpms increase


Ive generally selected one of the two lower designs in a 3000lb-3600 lb design for a serious BBC, and had them custom assembled by a good local shop

once your over about 600 ft lbs of torque you may want a dual disk design


BTW the upper clutch of the four in the thread above is easy to push in,smooth and quiet, but not nearly as strong as the lower designs,( its stock) the lower clutches are noticeably harder to depress, and can be noisy because theres movable weights and they tend too grab hard and faster , making the clutch engagement harsher but they tend too hold noticeably better also
heavy flywheels absorb, and dissipate heat better,they make the engine idle smoother they tend to make the car accelerate smoother and launch from a standing start easier, lighter flywheels allow the engine to accelerate slightly faster, or change engine rpms during gear changes a bit faster but remember the cars only getting power transferred to the rear wheels from the engine while the clutch is fully engaged.............think about that, youve got a 60-80 lb rotating assembly, including the crank, damper, rods pistons etc, spinning 1000-6000rpm and your debating reducing the effective weight 10-19 lbs with a lighter weight fly wheel , thats less durable, and its only advantage will be when its loaded against a clutch, and dragging a 3000-4000lb car along with it., on the street....the lure of light weight fly wheels comes from circle track racers who, need to use engine compression to slow the car coming into tight corners and need to blast out of those corners under wide open throttle conditions, there engines rarely fall below 4000rpm, under those conditions in a 1800lb-2500lb car it makes some sense, on a street car its a bad idea.
generally you should consider anything in a flywheel under about 20LB to be too light weight for daily street use, (most are undercut to reduce weight or aluminum, requiring friction contact pads, and don,t absorb heat, and dissipate it well unless the average engine rpms are fairly high) in the average engine combo used on the street,where launching the car smoothly from IDLE rpms is pretty much required and anything much over 35 lbs is not required either as flywheels above that weight are usually designed for high rpm launches with few gear changes where its almost mandatory to let the clutch slip while the drive train catches up with engine rpms.
for street use the 25lb-35 lb range flywheel is a good compromise for most cars, don,t forget a good quality sfi rated flywheel and blow proof bell housing could save your feet from a clutch/flywheel failure

the first time I replaced a clutch I was about 16,years old,
and I was so damn proud that Id managed to remove and replace the transmission and replace the clutch....
until I found it would not release once it was back together....
so I was forced to go ask this old geezer who must have been something like 50 years old...
that worked at the local Pontiac dealership, and he instantly deduced,
that Id installed the clutch disc facing the wrong direction, from the symptoms.....
Like I said, we mostly learn by making mistakes and if were smart,
and by watching other people make mistakes.

and you can bet you remember which way a clutch disc faces after that





typical clutch


typical clutch linkage
btw, if your old clutch is wearing its a good idea to get the cause diagnosed,inspected and perhaps have him suggest either better parts or have yours rebuilt,
bring your old parts (clutch, pressure plate, disc,throw-out bearing and flywheel to a good LOCAL clutch re-builder to have him resurface, the pressure plate, and flywheel, re-spring and replace the throw-out bearing and clutch disc, and inspect the used components as he will be able to give you good advice once he inspects the worn components, plus refurbished components should cost less than 1/2 the new price, and if hes a good knowledgeable guy they will be built to higher tolerances and IF you insist on the better components during the rebuild he will use a bit better quality springs etc.
most better shops have about a 24 hour turn around time, some in under 4 hours

http://www.jegs.com/p/J-W-Performance/J ... 7/10002/-1
you TH350 and TH400 guys need this also

Throwout Bearing Installation
Example of Correct Bearing Installation One of the most common mistakes made on GM vehicles - mostly pickups - is the improper installation of the throwout bearing onto the clutch fork. The spring (in black) on the clutch fork (in red) should be placed in the gap between the rear flange on the bearing and the front flange. You should not be able to see the spring on the back of the bearing. Symptoms of an improperly installed bearing are poor release, a mushy feeling pedal, short clutch life, and not being able to adjust for correct free play on mechanical linkage systems. This bearing and fork spring combination has been used from the late 1960's up to the present.









just a few thoughts, theres two potential ways to connect a pivot arm to a throw out bearing

THERES ALSO THREE COMMON INNER DIAMETERS to fit the sleeve on the transmissions 1 1/16:., 1 1/8" and 1 3/8" , if you get the wrong inner diam, it won,t slide back or it will rattle on the transmission


theres two basic throw out bearing designs, if your using the longer throw out bearing, in a application designed for a short or connecting the pivot arm incorrectly those could both be a problem

Full Size Chevy Clutch Release Throwout Bearing, Long, ACDelco, 1958-1972

Stock Replacement
1-7/8" Long
Diaphram Style Pressure Plate

This stock replacement long clutch release throwout bearing is manufactured by GM or by one of its authorized suppliers as a factory replacement part. You will find the fit and performance meets all GM specifications. Using stock replacement parts from Eckler's, such as this long clutch release throwout bearing, is a sound investment in the restoration or repair of your Chevy.

http://www.lategreatchevy.com/full-size ... -1972.html





Full Size Chevy Clutch Release Throwout Bearing, Short, 1958-1972

Stock Replacement
3-Finger Borg & Back Style Pressure Plate
Works With 3, 4, 5 Or 6-Speed Transmission

This stock replacement short clutch release throwout bearing is manufactured by GM or by one of its authorized suppliers as a factory replacement part. You will find the fit and performance meets all GM specifications. Using stock replacement parts from Eckler's, such as this short clutch release throwout bearing, is a sound investment in the restoration or repair of your Chevy.

http://www.lategreatchevy.com/full-size ... -1972.html
Last edited by a moderator:


Staff member
and yes,you'll want to verify the throw out bearing rides free of and back off the pressure plates spring loaded fingers,
(LIGHT GREEN AREA) when the clutch petals not being manually depressed






Pilot bushing clearance to trans input shaft should be .001 to .004
...with .002-.003 being considered about ideal




its not all that rare for the WRONG throw out bearing to be installed or the clutch linkage adjustment or clearances to be wrong if not carefully checked

other wise its going to result in much less clamping pressure and early clutch failure similar to riding around all day with your foot partly loading the clutch petal and causing the throw out bearing to constantly apply pressure on the pressure plate release springs, obviously if the throw-out bearing can,t fully dis-engage from the clutch pressure plate it prevents the pressure plate from reaching anything near full clamp loads and would have quickly resulted in a fried clutch

OBVIOUSLY theres a great many different applications and clutch and throw out bearing designs, but common sense should tell you the throw out bearing should be free of contact with the pressure plate m and recessed back away from the pressure plate on the transmissions collar held back in th clutch fork, when the clutch petal is not being manually depressed
the answer to what clutch design is best and how much clamp loads you want and how much clutch petal effort you want to put up with depends on the application.
If your wife drives the car and its used for daily transportation a dual disc clutch will allow a good deal more clamp surface without a huge increase in petal pressure , the increased surface allows the clutch to engage smoothly yet get a good grip. the ideal clutch depends on several factors, your budget, like the cars tire traction,limitations, how you drive, at what rpm you shift and launch the car, because the cars wheel spin acts like a fuse reducing loads on the clutch disc , its slipping that generates heat that destroys a clutch disc, but its the slipping that allows you to smoothly engage the engine to the drive train,and drive on the street,on a race car, if you power shift at 6000rpm most of the time a smooth transitions a bit less of a concern how you drive and the clamp load on the disc.
and how much clutch petal pressure your willing to live with.

I had a 1968 corvette with an m22 manual trans and 4.1:1 rear gears in a dana 60 with a custom 4 link rear suspension,equipped with a race 496 BBC engine with 13.7:1 compression and crower stack injectors,
the first couple years I used a single disc clutch, that looked a good deal like this, but it was custom assembled by a local clutch shop, and used on a 45 lb steel billet flywheel, theres springs under that cover that can be swapped out for stiffer springs , increasing the clamp load,the stock clamp load is usually about 2300 lbs, if you have a clutch shop install the stiffest available springs in all the locations 3900 lbs of clamp force is possible.
this came in very handy because the engine had over 650hp/650 ft lbs of torque ,it would smoke even 11" wide 30" tall race slicks if I launched at over 1900rpm. and I GOT VERY TIRED OF REPLACING THE STOCK l88 CORVETTE CLUTCH COMPONENTS, ONCE I UPGRADED TO THE STIFFER COMBO, I GOT MANY MONTHS OF RACING ON A CLUTCH DISC NOT JUST A FEW DRAG RACES, LIKE THE STOCK CORVETTE L88 CLUTCH ALLOWED
but keep in mind that more than triples the force required to depress the clutch petal and it becomes a real project to keep it pushed in, so much so that many guys can,t manage it., and it would never be a good option on the street car to custom build and install a 3900lb pressure plate.
this much clamp load would more than likely warp a stock or aluminum fly wheel



http://www.stangtv.com/news/video-comp- ... clearance/

http://www.ramclutches.com/Instructions ... 0Setup.htm


Ill second the advice on never useing the white litium grease on anything, like a pilot bearing!

especially roller bearings, the grease you want is BLACK, MOLY grease its designed for high heat and pressure levels, most auto parts stores carry it if you ask for MOLY AXLE GREASE

I look for and have found that American made billet fly wheels / clutches, in the 30-35 lb weight range with SFI certification numbers from HAYS,Centerforce , ZOOM, WEBER, all work reasonably well if you select the versions matching the application, get a good lakewood or other blow proof bell housing, you can,t replace feet, easily, but don,t over look your local clutch rebuilder, he may have deals that you can get if you ask.
All cast iron or cast steel fly wheels will eventually fail,
its just a matter of the abuse,heat,time and rpm and LUCK!

Im sure a 15lb- 26 lb aluminum, fly wheel will work,and thats what a good deal of road racers and circle track guys will recommend, especially in a race car application, but Id have selected a 30lb-35 lb in a street car, it will make street driving a bit smoother, keep in mind the fly wheel inertia increases dramatically as the rpms increase so a race car engine operating at a much higher average rpm level can effectively use a lighter fly wheel, and if you spend all most all your time running the engine well above 4000rpm theres little reason for the heavier flywheel.
as always Id suggest calling a minimum of 3 vendors and talking to the tech guys to get a feel for customer support and get a few questions answered

Lubriplate makes a moly grease used for construction machines and other types of exposed gears and bearings. It is a tacky grease that will not spray out of bearings or off of open gears. It is called No 3000 Heavy Duty Tacky Moly Grease,(part # l0108-098). A large tube costs about $ 3.50 and can be found at any bearing supply house or construction machine supplier. This grease is a black soft grease that is very sticky to itself and whatever it is on.

don,t forget to install a pilot bearing in the rear of the crank too support the front of the transmission splined input shaft, btw you remove the old one "IF" it needs to be replaced by packing the area behind and inside it with grease and hydraulically lifting it out by use of a wood dowel driven into its center area with a mallet, the displaced grease forces the bearing up and out
[grumpy?]how do get the grease behind the bearing? [/quote]
thru the center hole the tip of the splined trans shaft rides in










http://www.carolinaclutch.com/Content/C ... g.htm.aspx

http://www.lubriplate.com/pdf/pds/3_21 3000 Series.pdf

btw heres moly assembly lube


http://www.ramclutches.com/critical%20d ... wheels.htm

DON,T forget youll want to RESURFACE GRIND the flywheel , and pressure plate surfaces if you re-use those parts, because once its worn on an old clutch the surface tends to warp with heat,and you want the new surface to provide the new clutch with a consistent surface finish if you want the new clutch disc to last.
most issues with a clutch "chattering" are the result of an un even clamp surface like a warped or heat spotted surface on the flywheel or pressure plate.
Id also point out that many racers have the flywheel and pressure plate balanced as a matched set, and IF thats been done, there will usually be a index mark on both the pressure plate and flywheel to indicate proper re-alignment if disassembled for re-assembly. so look for those and make darn sure that any balance index marks are duplicated on BOTH the pressure plate cover and edge of the flywheel so surface grinding to recondition the clamping surfaces won,t remove them (usually a (B) stamped in both the pressure plate and flywheel edge surface but some times just a punch mark)

AN SFI RATED BILLET STEEL FLYWHEEL IN ABOUT A 30 LB-35 LB weight is about the best choice in my experience for a street / strip car that weights over 3200 lbs, AND I CERTAINLY PREFER THE BORG AND BECK STYLE PRESSURE PLATE


borg & beck


old warn and warped a bit
a shudder as the clutch is engaged,
often the result of worn or contaminated clutch components.
(oil on the disc)
a worn flywheel or heat warping or a well-worn disc
The clutch disc is grabbing and releasing the flywheel and pressure plate as the assembly is turning.
It happens very quickly as the engine is rotating.









refinished ground
Last edited by a moderator:


Staff member
why does an 11 inch clutch have noticeably more holding potential than a 10.4" clutch? Well,keep in mind the inside hub takes up a good deal of the central area
read the links


the contact surface is about 3" wide on either clutch and the central hubs are fairly consistent
so on a 10.4" clutch the area is about 35- 40 sq inches of surface area less than a 11 clutch (brands and designs vary)and remember your(counting BOTH sides of the disc contact surface area ) simply because the circumference on an 11" clutch allows a .60 wide band on the outer circumference where it does the most good physically due to leverage

got more money,and a need for still more clutch? a dual disc clutch increases the contact area much more

BTW if you don,t connect the throw out bearing to the clutch fork correctly the clutch is harder to use and the petal sits noticeably lower in many cases, if you don,t use the correct type or height of throw out bearing for the type of clutch the petal height and geometry changes.


theres long and short throw out bearings several different clutch fork designs and pivot ball heights


If thats what your problem is it sounds like the throw out bearing is not connected to the clutch fork properly, if the clutch WON<T disengage at all the fork may be broken or the clutch disk may be facing the wrong direction, 180 out,(flywheel side facing the clutch)

http://www.hurst-drivelines.com/files/C ... _instr.pdf

http://www.hurst-drivelines.com/files/C ... n_Tips.pdf



remember theres two different designs, and use of the wrong one in your application will cause problems

Ive used these brands,on most of my personal cars, what you use usually depends on price and application
naturally you can shop on line and get some decent products or occasionally cheap junk, its usually best to either work with a local shop you trust, that can custom assemble components to your specs with their experience and input, or buy brand name products.
youll need to measure the flywheel as some can take both a 10.4" or 11" clutch , but some can only take the smaller 10.4" and flywheels come in 153 and 168 tooth diam. designs and not all applications or bell housings allow interchanging component sizes, the larger 11" clutch obviously has a distinct advantage in that theres a greater surface area and better heat distribution and a bit more leverage the disc surface area provides but your limited to what fits the application, or you can upgrade to a dual disc clutch in some applications effectively doubling the disc surface area









http://www.summitracing.com/search/Make ... ut+bearing

http://www.classicparts.com/1947-75-Clu ... fo/90-205/

http://www.classicparts.com/1955-84-Clu ... fo/90-211/


standard diaphram

weighted diaphram


borg & beck


long style
Last edited by a moderator:


Staff member
Lakewood Safety Bellhousings
Quick Time Bellhousings


http://www.browellbellhousing.com/pages ... -page.html

http://www.corvetteguys.com/corvette-cl ... ction.html

http://www.gmpartsdirect.com/performanc ... D=913.html

http://www.s-series.org/htm/tech/GMPerf ... 76-081.pdf


ALWAYS ask the tech support guys ALL the questions you can think of about clearances, compatibility, suitability, ask for suggested matched parts, info, etc. BEFORE ordering parts

If your going to use SLICKS the tire compound selected, the air pressure ,your driving style, the engines torque curve, if you use a traction compound , if you run only after several burn-outs to heat the tires, or just roll up and launch, all effect your results,
without knowing your engines power curve,car weight, transmission gearing,stall speed or clutch, the rpm range you currently launch at,the surface you run on, the rpms you go thru the lights at, the current traction issues if any, and how the cars suspensions set up, your 60 foot times and several other factors (a video of a current launch would help), your just guessing, if you have that info your still guessing but you can get MUCH MUCH closer to ideal results
a leaf spring car with traction bars, launches different than a 4 link or a ladder bar car etc.
knowing a good deal more about the application improves the chances of building a working suspension, you certainly don,t want the front wheels 6 feet in the air ,or the differential ripping the frame and suspension components loose or busted axles, you want rapid acceleration with max weight transfer, while still maintaining steering control and not busting drive-line or axle parts
Last edited by a moderator:


Staff member

http://www.centerforce.com/?gclid=CODF_ ... 7Qodt0RfZQ



http://www.powertraintech.com/Files/PDF ... 0Facts.pdf



http://www.haysclutches.com/pdf/Perform ... h_Kits.pdf



http://www.corvetteguys.com/corvette-cl ... ction.html

http://www.competitionplus.com/04_15_20 ... univ3.html

early GM (60s, 70s, 80s) Flywheel and Clutch Info:

The following information is based on GM production combinations, and is by no means complete and thorough. You’ll need to confirm what you actually have in your car, as things change over the years, especially with aftermarket parts, block machining, etc.

2 Flywheel sizes:

* 153 tooth, 12.75” diameter. Used on 350ci and smaller engines.
* 168 tooth, 14” diameter. Used on SBC and BBC, 400ci and larger

2 Flywheel weights:

* Internal Balance; Engine is balanced internally, and the flywheel neutrally balanced. Used on SBC 350ci and less, 427 BBC and less
* External Balance; Engine is balanced externally, and the flywheel has a counter balance weight. Used on SBC 400ci, and BBC 454 and up.
* It is possible and common to change an externally balance engine to be an internally balanced engine.

The GM engine blocks are machined to accept 2 starter bolt patterns:

* Straight across pattern; always for SBC, and always for the 153 tooth flywheel
* Diagonal pattern; always for SBC 400ci, and all BBC blocks, and for the 168 tooth flywheel.
* Both patterns; 350ci and less SBC often have both patterns, and can accomodate either flywheel size.

There are 3 clutch sizes:

* 10.4”; the most common (aka the “10 1/2” clutch)
* 11”
* 12”; for truck applications

The 10.4” and 11” clutch can be used on either flywheel, and your choice depends on the clutch pressure plate bolt pattern. Generally, the 11” clutch will only fit on a 168 tooth flywheel, however, aftermarket companies do sell a pressure plate for the 153 tooth flywheel and and 11” disc.

The 153 tooth flywheels generally have a 10.4” clutch.

The 168 tooth flywheel can be ordered to accept either a 10.4” or 11” clutch.

Similarly, you can use a 12” disc with an aftermarket pressure plate on a 168 tooth flywheel. McLeod sells such a package.

2 flywheel types based on rear main seal:

The early GM blocks had a 2 piece rear main seal, and the later models had a 1 piece rear main seal. They flywheels are different for each, and more info is coming on this topic.

Which flywheel diameter is right for me?

Well, that’s mostly dictated by which block you have, and which starter bolt pattern(s) you have. However, it is possible to have the block machined and tapped for the opposite bolt pattern, and/or to purchase an aftermarket mini-starter that will allow either flywheel.

Which clutch size is right for me?

Boy, there’s lots of opinions on this question. Here’s mine. Unless you’re running really high HP/Torque, and just want every last ounce of gripping power, get the 10.4” clutch. Why? The 10.4” is plenty of clutch for most applications, especially street car applications. Your radial tires will spin long before a 10.4” clutch slips. Also, the 10.4” clutch has less rotating mass, which will result in a better shifting transmission (because the addtional centrifical force of the larger disc will keep the input shaft spinning, and the input shaft must slow down in order for a smooth shift). Further, bear in mind that clutch technology has improved dramatically over the years. Even 30 years ago, the 10.4” clutches were used behind the Hemi engines. If Mopar felt that a 10.4” clutch was good enough for them back then, it stands to reason that today’s much improved clutches will work even better.

If you’re running slicks, and a high HP engine, then by all means, the additional gripping power is a good thing.

If you don’t agree, that’s ok. It’s just my opinion, I’m not a clutch engineer/designer. :)
I always recommend that you ask around, ask the experts, and take what you feel are the best recommendations that suit your needs. It’s always good to do your homework, and get the varied opinions so that you make knowledgeable decisions.


http://www.modernperformanceclassics.net/ShowItem/102808 62-67 Nova Clutch Adapter Bracket.aspx
More about clutches:




Tech Alley "Where you find all the answers."

CLUTCH TECH - How to Choose the Right Clutch
With an explanation of clutch technology, Modern Driveline shows you how to choose the right clutch for your driving style and usage.

Although clutch and flywheel selection seems like black magic science, it really is straightforward. When the right choices are made you get an unbeatable clutch and flywheel combo that will serve you well for years to come. In the long run, you will save a bunch of money with the right decision to begin with. And can you afford to make a bad decision? Think about it.

Karl Benz is generally recognized as the father of the automotive clutch, which was invented nearly a century ago. There have been many variations of the humble hard-working clutch in the years since. The clutch’s primary task is to transmit power from the engine’s crankshaft to the transmission smoothly and firmly without slippage. Some slippage is important for smooth engagement, yet without excessive slippage that will cause unnecessary wear and heat issues. You want reasonable pedal effort yet solid engagement, which is what you will get from our Superior clutches.

Clutch selection depends upon the kind of driving you intend to do. If you’re going cruising or doing the workday commute, you need a high-quality diaphragm style single disc organic clutch. Organic clutch frictions provide smooth engagement and longevity in street use. Weekend racing calls for a Kevlar/organic combination. And if you’re real serious about performance driving, a Kevlar high-performance clutch is what you’re going to need to meet the demand.

Clutch Types
There are two basic types of clutches — diaphragm and Long style.

Long Style
The Long Style three-finger clutch was original equipment in a lot of vintage applications. Because the three-finger clutch and pressure plate exert incredible amounts of pressure they also create tremendous amounts of clutch pedal effort. Back in the day a stiff clutch pedal was the norm, but not anymore. Clutch technology has since become such that you don’t have to put up with a stiff clutch pedal (or the resulting knee replacement surgery) anymore. We can’t think of any reason here at Modern Driveline why you should have to put up with a heavy-handed clutch pedal.

The Long Style clutch consists of:

  • Pressure Plate Cover
  • Pressure Plate or Head
  • Fingers or Levers
  • Fulcrum Pins
  • Coil Springs
  • Clutch Disc or Friction
Now that’s a lot of parts!

The Long style three-finger clutch exerts brute pressure on the disc via a series of coil springs between the cover and plate. Spring pressure is the same regardless of engine rpm. Pedal effort is also the same regardless of engine speed. The Long Style clutch is an archaic design at best. It doesn’t make sense to use one anymore.

Diaphragm Style Clutches
Diaphragm style clutches, as the name implies, consist of a diaphragm spring that “oil cans” between engaged and disengaged. It is easy to depress yet it delivers whopping hold power. The advantage of a diaphragm clutch is greater clamping power than a conventional three-finger Long style clutch yet without high pedal effort. What’s more, as diaphragm clutch discs wear clamping power increases over the life of the clutch, which improves clutch performance. This is one of the great advantages of a diaphragm style clutch. Another advantage is pedal effort, which is considerably less than a Long style clutch.

Although there are a lot of diaphragm style clutches in the marketplace Modern Driveline brings you a better clutch and here’s why. Modern Driveline brings you greater selection with a complete line of clutches and flywheels from the most trusted names in the industry — Superior and McLeod. We enjoy an extraordinary relationship with Superior Clutch because each clutch is handcrafted for Modern Driveline. Each Superior clutch goes through rigorous testing throughout the manufacturing and quality assurance process resulting in high reliability and performance.

A lot of manufacturers talk about Kevlar clutch frictions, yet in truth their clutch discs contain a very modest amount of Kevlar — some 10-20-percent — which isn’t saying much. Superior Clutch’s disc are nearly 100-percent Kevlar, which can stand extreme punishment and come back for more as hard miles are driven. If you’re a civilized driver your Superior Kevlar clutch from Modern Driveline may well be the last clutch you ever buy. They’re that good.

Clutch Need To Know
We can get into a lot of clutch science and physics. However, here’s what you need to know in order to make an educated purchase. There are four Modern Driveline clutch discs from Superior Clutch for your consideration — Organic, Kevlar/Organic, Kevlar/Kevlar, and Kevlar/Metal.

The Superior Organic clutch from Modern Driveline is a basic stock replacement in either 10" or 10.5" and with either a standard pressure plate or the brute King Cobra pressure plate. The Superior clutch is economical and well suited to the daily/weekend driver or show car. The Superior Super King Cobra clutch from Modern Driveline features steel backed facings to prevent disc separation common with original King Cobra clutches and heavy abuse.

Modern Driveline’s Superior Kevlar/Organic clutch is a multi-friction type with Kevlar® and Organic surfaces designed with additional grip in mind and high heat tolerance from high performance applications. These clutches are available in 10" or 10.5". The Superior Kevlar/Organic clutch is optimum for street and track use.

Superior Clutch’s Kevlar/Kevlar clutch from Modern Driveline is designed for long life and minimal wear under extreme duty conditions. These heavy-duty clutches available in 10.5” are preferable for the high performance, high torque applications. What’s more, they’re preferable for lightweight vehicles prone to clutch chatter.

The Kevlar/Metal discs are designed for high horsepower, drag racing or street performance where "grab" is the name of the game. These are typically considered an "on/off" clutch. You cannot "feather" them for smooth street driving.


Fig. 1: Side by side are the two basic types of clutches — diaphragm (left) and Long style (right). By design three-finger Long style clutches yield a very stiff clutch pedal. Diaphragm style clutches provide a powerful grip without a stiff clutch pedal.

Fig. 2: Two organic clutch discs — coarse tooth (left) and fine tooth (right). Clutch discs are generally designed for application (size and transmission input shaft) the type of use they will experience. Organic clutch frictions are for mild street use.


Fig. 3/4 Here’s why the Long style three-finger clutch gives us such a stiff pedal — powerful springs that provide exceptional holding power. However, they also make it very hard on your left leg and mechanicals because pressure plate holding pressure is transmitted directly to the clutch pedal linkage. This really is an outdated clutch design when there’s a better choice.

Fig. 5 The diaphragm clutch is simply a better piece by design because it gives us great holding power without a stiff pedal. This is a small light-duty diaphragm pressure plate.


Fig. 6/7 Here’s another larger diaphragm clutch and disc for GM applications with fine-tooth clutch disc. .

Fig. 8 The beauty of the diaphragm clutch is simplicity — fewer parts. This link ties the pressure head to the backing plate.

Fig. 9 These coil springs act as shock absorbers in a clutch disc. This is what gives us a smoother engagement as the clutch disc and pressure plate take hold.

Fig. 10 Diaphragm clutch fully engaged with clutch disc compressed.

Fig. 11 Organic and Kevlar clutch discs back to back. On the left is the organic friction disc, which is thicker and heavier. On the right is the lighter and tougher Kevlar disc. Superior Kevlar discs are nearly 100-percent Kevlar designed to take the extremes of racing. Organic discs are strictly for street use.

Fig. 12 From left to right are metallic, Kevlar, and Organic discs

Fig. 13 Here’s the Superior diaphragm clutch with organic friction for street use. The organic disc will not stand up to the punishment associated with racing. This is a coarse tooth hub for vintage Ford applications.

Fig. 14 This is a Kevlar clutch friction in fine-tooth for GM applications. A fine tooth hub provides greater strength because there’s more shaft and hub surface area. Kevlar can be used for street and strip, however, it is primarily a racing clutch. It can take tremendous punishment and come back for more.

Fig. 15 Here’s a closer look at the Kevlar surface. All of our Superior Kevlar clutches are nearly 100-percent Kevlar for extraordinary durability and long life. Kevlar doesn’t look all that intimidating but don’t let looks deceive you. Kevlar is the toughest clutch material available. If you buy it for street use you will never have to buy another clutch.


Fig. 16/17 Here’s a metallic Superior clutch for all-out racing applications. This pressure plate is for GM products. As a rule most GM applications employ a fine-tooth input shaft.

Fig. 18 We also stock McLeod dual-friction diaphragm style clutches for performance applications. Choice depends upon how much power you have and what you want your vehicle to do.

Fig. 19 Here are the input shaft types you can expect to see for domestic applications. These are clutch alignment tools. Two from clutch kits and one copped from a Ford transmission. The steel input shaft works well as a clutch alignment tool. Our Superior clutches come with a clutch alignment tool for your convenience.

Fig. 20 Clutch pilot bushings (right) are typical for OEM installations. Compliment your Modern Driveline clutch installation with a pilot bearing (left) for precision function and smooth clutch operation. While you have your vehicle apart check the engine oil pan gasket, rear main seal, and transmission input shaft seal for leakage. Any leakage issues must be handled at this time or you wind up with clutch disc contamination.

Fig. 21 Clutch release bearing to diaphragm alignment must be spot on for proper function and longevity. Diaphragm style clutch release bearings are constant duty parts meaning they’re in contact with the diaphragm at all times.

Fig. 22 Compliment your new Superior clutch installation with a new flywheel from Modern Driveline. This is money well spent because every new clutch deserves a new flywheel surface. We stock steel, billet, and aluminum flywheels for nearly every application imaginable.
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Staff member
a toasted or burnt clutch disk and burnt or warped pressure plate is frequently the result of , and indication of,the power applied being greater than the clutch can easily handle, remember a slipping clutch disk builds up a great deal of heat, if you've ever seem disc brakes glow on a race car at night you'll have some idea as to the heat that can be generated, the problem comes down to a slipping clutch that generates a good deal of heat, in most cases that because the clutch either did not have enough surface area or clamping loads, or on occasion the person operating the clutch doesn,t shift properly. but in most cases its the fact the clutch surface area is too small (you need a larger diam. clutch or a DUAL or MULTI DISC DESIGN) or stronger spring rates and or more springs which will noticeably increase the petal force needed to depress the clutch and tend to make it grab far faster and HARSHER, which is no big deal on a race car but it might be a P.I.T.A. if the wife needs to operate the clutch and she can,t get it to depress enough to release properly.
it was not uncommon on high horsepower corvettes in the 1960-1990s to upgrade the 10.4" clutches in corvettes to an 11" design that produces a noticeable improvement in clamping power, that does require a different flywheel, pressure plate and disc and in some case a rotating assembly re-balance.


ook closely at this long style pressure plate assembly, notice the corner holes show springs while some holes don,t, most good clutch shops can install far stronger springs and do so in all the potential locations, increasing the clamp force from about 2300 lbs to over 3800lbs with 9 heavy springs vs just 6 standard springs in most clutches if they have experience building race clutches, but it takes a fairly strong driver to push and hold down a clutch that can require double, triple or quadruple the pedal pressure of the stock components, and a stronger clutch linkage and shorter throw out bearing life (not a big deal on a race car) so most clutch shops are reluctant to do the custom assemblies, build a clutch designed for really effective race use and your not going to be able to let the wife drive the car if she can,t depress the clutch, and it won,t be fun to drive in traffic either, you'll learn to speed shift due to necessity with some clutches that are basically pushed in or clamped with negligible slippage between

if the heavy spring load design 11" clutch designs won,t keep up with the power, CROWER makes a nice (EXPENSIVE) multi disc 11" that will!




Staff member
Each time you disassemble the clutch the flywheel and clutch need to have a detailed visual inspection and only experience will help detect flaws so take it to a machine shop and pay for a MAGNAFLUX check if your in ANY DOUBT, your local clutch shop should check if your in ANY doubt


http://www.extremehowto.com/xh/article. ... e_id=60306





Staff member


http://www.mcleodind.com/application_gu ... _2006.html

http://www.mcleodind.com/downloads/prod ... Page_9.pdf


keep in mind theres three common throw out bearing heights and youll need the correct height for your particular application to get proper clutch function
If your looking for a good quality clutch/pressure plate, etc,
ID CALL THESES GUYS and get them to suggest a part number for a LONG or BORG AND BECK clutch that fits YOUR application
now be sure you describe exactly what YOU want, I always wanted the max springs, in my BIG BLOCK VETTES but the pedal pressure to work the clutch requires a great deal of effort and its not necessary unless you've got far more than 400 hp,
keep in mind you want a SFI BILLET flywheel and a BLOW-PROOF BELL HOUSING

ONE REASON I TEND TOO STRESS THE USE OF both A LAKEWOOD BELLHOUSING AND A SFI RATED BILLET STEEL FLYWHEEL, AND A SFI RATED PRESSURE PLATE , is that over the last 45 or so years Ive personally seen the results of at least 6 cases where clutches or flywheels came apart at higher rpms, the results can nearly cut the car in half without a blow proof type bell housing


now in this thread and its related sub links
we discussed fuel line size and the fact that quality AN#8 fittings, are far less likely to pose a significant restriction to fuel flow rates in most performance applications and that a quality fuel filter must be used rather than the cheap off the shelf plastic or glass fuel filters you occasionally see used.

Based on this NHRA rule

Lines: All non-OEM fuel lines (including gauge and/or data
recorder lines) must be metallic, steel braided, or NHRA-accepted
“woven or woven-pushlock.” A maximum of 12 inches total (front to
rear) of non-metallic or non-steel braided hose is permitted for
connection purposes only; individual injector nozzle and motorcycle
fuel lines are excluded. Fuel lines (except steel braided lines) in the
flywheel/bellhousing area must be enclosed in a 16-inch length of
steel tubing, 1/8-inch-minimum wall thickness, securely mounted as
a protection against fuel-line rupture. Fuel lines may not be routed
in the driveshaft tunnel. It is mandatory that fuel lines passing
supercharger drive belts be steel braided, NHRA-accepted woven
or woven-pushlock, or be enclosed in protective steel tubing. A
current list of NHRA-accepted woven or woven-pushlock fuel lines
is available on NHRA.com. All NHRA-accepted fuel lines must use
ends that are specifically designed for the type of fuel line being
used. No hose clamps allowed on NHRA-accepted fuel lines.
Pumps/Valves: Cars with non-OEM-type mechanical fuel pumps
must have a quick-action fuel-shutoff valve within easy reach of
driver and located in the main fuel line between the fuel tank and
the carburetor and/or injectors. Fuel recirculation systems not part
of normal fuel/pump system prohibited. All cars in Stock, Super
Stock, Competition, and Pro Stock must be equipped with a
positive-lock drain valve located between the fuel tank and the
carburetor(s) or fuel injector to facilitate removal of fuel samples for
fuel-check purposes

if youve ever seen an engine puke a connecting rod at 6000 rpm plus,
you know the vast majority of the full 5-8 quart oil pan capacity can be almost instantly,
thrown under the car, this alone generally can cause the car to loose control even if the driver keeps his cool, during a cataclysmic,
engine failure, so having a lakewood or similar blow proof sfi rated scatter shield,
bell housing and a engine diaper are required in many of the faster racing classes

for those without access to the current/2019 NHRA Rule Book


In classes where specified, must utilize an NHRA-accepted lower
engine oil-retention device. SFI Spec 7.1 or 7.2 Lower Engine
Containment Device permitted. A properly fitting lower engine
ballistic/restraint device mandatory. The NHRA Technical staff
can accept or reject any device. Any device that fails to perform
as required must be replaced or repaired to the satisfaction of
the Technical staff prior to any further runs. When used, an SFI
Spec 7.1 or 7.2 Lower Engine Containment Device must cover
the sides of the block and pan up to within one inch of the head
mating surface and extend to within 1 1/2 inches of the front
and rear of the cylinder case area. SFI Spec 7.1 devices must
be updated/recertified by the original manufacturer at one-year

In classes where specified, a belly pan may be used in
lieu of a device attached to the engine. The belly pan must extend
from frame rail to frame rail and extend forward of the harmonic
General Regulations Section 21, page 9
General Regulations balancer and to the rear of the engine block and must incorporate a minimum 2-inch-high lip on all sides unless specified in Class
Requirements. Minimum number of slots or holes in the walls to
clear frame, steering, or lines permitted. A nonflammable, oil absorbent
liner mandatory inside of retention device.


engine diapers made from nylon are a waste as header heat rapidly melts holes, making them useless
you want, in fact NEED a nomex and kevlar oil pan diaper to be legal in the faster classes,
and yeah its damn expensive, but serious race cars are a bottomless money pit.

but Id point out that routing your fuel pressurized and return lines away from the exhaust header heat or in areas potentially impacted by a failed drive shaft or an exploding clutch assembly only makes good sense, and a bit of ARMORING in areas you cant avoid by running lines thru a larger short section of 1"-1.375" section chrome moly tube,thats a minimum of 1/8th inch thick, that will weight less than a lb or two, to act as a shrapnel deflector makes a great deal of sense.
a 24"-to-36" section of custom bent armor tube thats solidly clamped to the frame ,protecting the fuel lines run thru it in the area near the headers and bell housing can save you a great deal of damage or the car catching on fire if the armor prevent fuel lines from being cut in a clutch of converter failure

http://www.onlinemetals.com/merchant.cf ... &top_cat=0


RELATED INFO, with lots of optional , and useful info, failure to take the time to read thru the linked info could eventually cost you far more than the time it takes to read the links









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Staff member
lsejlowe posted this

I don't know jack about clutch wear. What do you guys think of these pics? I know that there's no better time to replace it, but if I can save the cash for now and replace it when I convert to a 5 speed that would be a much better option for me.




Pilot bushing clearance to trans input shaft should be .001 to .004

...with .002-.003 being considered about ideal,and the common brass pilot bearing

should be greased on install, but manufacturers parts vary and .005-.006 clearance to account for a bit of bell housing miss alignment and heat expansion is common.

the surface of the flywheel appears to have little radial cracks: these are a indicator the fly wheel might be prone to coming apart under high rpm stress loads, like a quick shift under load...yeah! I know you know someone who has run a flywheel like that for years with zero problems.......its your feet and its just a mater of time.....



clutch disk:


Pressure plate:

surface looks really good to me:

clutch fork stud:





What else should I be looking for? Spring damage? Other wear points? I think I'll replace the throw-out bearing while I'm here since it'll be relatively cheap, but I'm inclined to just leave the rest of it. What would be a typical cost for resurfacing the flywheel?
keep in mind a SFI SCATTER SHIELD to protect your feet is almost mandatory, KEEP IN MIND THE COST OF A good SCATTER SHIELD/ BLOW PROOF bell housing is a lot cheaper than having your legs amputated by flying chunks of metal on a high performance engine combo
a stock bell housing provides almost zero protection if a flywheel or clutch comes apart at high rpms, and getting your feet cut off in the process is not unheard of as a result

if a clutch fails shrapnel , can and will punch thru the floor of the car and your feet frequently







more pictures showing the results of a STOCK STYLE , NON SFI RATED flywheel coming apart , luckily this guy had the foresight to use a blow proof bell housing so he only lost an engine not his feet, but even with the blow proof bell housing look at the damage that resulted

they also sell auto transmission shrapnel resistant safety blankets, and converter shield plates which are an excellent idea, for what should be obvious reasons







watch THESE (found on youtube)

http://www.youtube.com/watch?v=tDbrvUtN ... r_embedded


don,t get the idea that a torque converter can,t fail either, if your racing youll want a transmission safety blanket







just because heavy jagged chunks of hot steel tend to exit through your floor, dash and wind shield with enough force to cut the cars frame in half at times when a cast flywheel comes apart at higher rpms is reason enough to use billet SFI parts and a blow proof bell housing







read ALL the links
since youve already replaced the clutch disc and pressure plate, I'd point out that,
many times clutch chatter is the result of an un-even flywheel surface, any decent machine shop can surface grind the existing friction surface a few thousands to correct that issue.
clutch chatter is the result of un-evenly applied clamping surfaces, usually a high spot(S) on the clutch pressure plate its housing or the flywheel surface, but grease and or oil on the clutch disk, or loose disc pads could also be too blame , but heat warping or a broken spring or mis-aligned spring will also cause this symptom.
the flywheel should be torqued to the crank flange, an impact gun should never be used as its possible to warp the mount surfaces is tightened un-evenly
if the clutch vibration does not go away once the clutch locks up,
you've more than likely,
got a drive line component alignment or rotation assembly or drive line balance issue.
you'll want to verify the flywheels mounted so its not wobbling, it may be warped,
or the crank flange its mounted too has been bent or theres debris between the flywheel and crank flange,
you,ll want too use a dial indicator mounted on the block and rotate the flywheel to find out,
if the flywheel friction surface or outer diameter
,changes its distance from the block as it rotates




Chattering is a grabbing or jerking condition that occurs when the clutch is engaged. Clutch chatter is often caused by oil or grease on the clutch linings, but it can also be caused by burned or glazed linings, a warped or grooved flywheel, missing flywheel dowel pins, a worn pilot bearing/bushing, a worn bearing retainer, worn or damaged clutch disc or input shaft splines, bent or broken drive straps on the clutch, a bent or distorted clutch disc, a loose clutch cover or even missing flywheel dowel pins.

External causes of clutch chatter include loose or broken engine or transmission mounts, misalignment of the chassis and drivetrain components, worn or damaged U-joints or CV joints, a loose transmission crossmember, a worn or bent release fork, or loose rear left spring bushings or spring U-bolt nuts.


read ALL the links











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Staff member
those heat cracks in the FLYWHEEL , caused by heat.& cool cycles on the cast steel, are an indicator that the cast flywheel is potentially only over time going to eventually get worse and break,resurfacing will hide the cracks but they extend deeper than the surface and resurfacing will not cure the problem, the pressure plate looks good the disc is re-useable but it SHOULD BE REPLACED as its a P.I.T.A. to go back and do it later and its thickness from the rivets, holding the contact pads looks about 1/2 way thru its life expectancy
ID replace the flywheel with a BILLET SFI STEEL 30-35LB design and add a blow-proof bell housing if you like having to operational feet, now don,t get me wrong , it might last for many years,without failing or it might come apart violently after several hard shifts, but you can,t replace feet that get cut off....your call!
yeah I know another EXPENSE! think what replacing your dash, bell housing, clutch, interior and feet might cost????

watch THESE (found on youtube)

http://www.youtube.com/watch?v=tDbrvUtN ... r_embedded


http://www.hurst-drivelines.com/files/G ... 15-09A.pdf







IF your having a clutch engagement issue , check out the Z bar and linkages as well as the clutch , throw out bearing , it would certainly not be the first time the linkage geometry, caused an issue with clutch operation.
I know Ive had to cut and re-weld or even fabricate from scratch, several (Z) bars as to the arm length and angles over the decades

http://www.chevyhiperformance.com/techa ... age_build/





look over the clutch linkage diagrams in the links below, if your not familiar


http://www.hurst-drivelines.com/files/C ... n_Tips.pdf

http://keenparts.com/pages/catalog2.php ... 0&year=ALL





keep in mind some engine blocks require an adapter plate to mount a Z bar for a manual clutch


Remember that the new Mark V big blocks do not have a boss to mount the z-bar pivot ball if using a manual transmission. A bracket can be made to bolt on to the bellhousing to hold a welded on ball stud if needed. Mark V big blocks also do not have provisions for a mechanical fuel pumps and you will need to mount an electric pump near the fuel tank. The latest Mark VI engines have fixed both of these inconveniences. With both of these engines the supplied oil pan will not fit the Chevelle chassis, Moroso and Apple Chevrolet in York, PA (Area code 717) both offer oil pans to fit the Chevelle. Even with these oil pans early Chevelle (64 to 67) steering linkage will hit, so some minor clearancing must be added with a hammer.
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Staff member











Twin-Disc Clutches Breakdown - Quick Tech
From the July, 2010 issue of Car Craft
By Jeff Smith
Photography by Jeff Smith

Twin-Disc Clutches
Dual-disc street clutches are now gaining popularity mainly due to the stupid amount of 21st century power car crafters are making. This puts the arm on transmissions, torque converters, and especially clutches to transfer all that power without failure. The answer to a stronger clutch is not necessarily a stiffer pressure plate. The torque capacity of any clutch is based on three basic parameters: clamp load, surface area, and coefficient of friction. Increasing any of these factors (like surface area) allows the designer to change the other two variables. As an example, by doubling the clutch surface area with the same coefficient of friction, a single-disc clutch that can hold 500 lb-ft can now reliably hold 1,000 lb-ft. Centerforce has come up with an innovative variation to the two-disc street clutch that is so new it still doesn't have a name. The most interesting part of the clutch is the hub-pin drive that connects the primary and secondary discs. One issue with dual-disc clutches is there is limited room on the transmission input shaft for two splined hubs. By pinning the two clutches together, the second clutch disc does not need hub springs, reducing the weight of the second disc. As you can see, the company put some serious engineering into this design.

A. The flywheel generally supplies the most weight in the clutch system. Heavier flywheels store more energy than lighter flywheels at the same rpm (assuming the same diameter), which becomes evident when attempting to accelerate a heavy car from a stopped position. The energy stored in the flywheel is subject to something called rotational inertia that increases when additional mass is located farther away from the centerline of rotation. So a larger flywheel with more weight concentrated on the outer ring of the flywheel will require more power to accelerate. Given this, Centerforce reduces the weight located at the outer edge of the flywheel to improve acceleration. Removing the same amount of weight closer to the center of the flywheel would not improve acceleration as much as removing the weight farther away from the centerline.

B. Dual-friction discs are also part of this twin-disc clutch with a high-temperature organic (nonasbestos) material on one side of the clutch face and Centerforce's metallic-ceramic alloy on the other. This combination of friction materials allows the clutch designer to increase the holding power while still delivering a friction surface that is not too aggressive.

C. The Centerforce clutch reduces weight in the second disc by using the drive lugs to directly connect the primary clutch disc with the nonsprung secondary disc. The secondary disc relies on the springs in the primary disc to eliminate chatter.

D. All street clutch discs require a spring-loaded hub that tends to absorb the clutch material's initial hit during engagement. The springs damp the initial oscillations of the clutch disc, minimizing potential clutch chatter.

E. The clutch hub is designed with a softer steel alloy than what is used in the input shaft of the transmission so it will wear before the transmission shaft. One key to a quality clutch is how well the splines on the clutch hub fit over the transmission input shaft. Sloppy spline teeth from an inexpensive clutch can cause all kinds of clutch engagement issues and contribute to input shaft wear.

F. Virtually all street clutches also employ what is called a Marcel spring between the two facings of the clutch friction material. This is a very thin, wavy spring that also helps to damp the chatter of the engaging clutch. Race clutches do not employ a Marcel spring and can be very harsh on the street as a result.

All dual-disc clutches must employ a midplate or floater secondary flywheel surface that is attached directly to the flywheel. It provides a flywheel surface connected directly to the crankshaft for the secondary clutch disc. This surface must float when clutch pressure is released (clutch pedal depressed), which is where the device gets its name. With this Centerforce unit, the floater is connected to three large drive pins located on the flywheel.

G. Drive straps are the direct connection between the pressure plate cover and the iron pressure plate ring. Under acceleration, these straps are under tension (pulled apart) as the pressure plate is clamping the clutch plate against the flywheel. Under deceleration (such as an abrupt downshift), the pressure plate ring attempts to compress the straps. If the downshift is severe, these straps can buckle. Once that occurs, the pressure plate must be replaced.

H. There are three styles of pressure plates used in performance applications. The most popular street pressure plate is the diaphragm (used on the Centerforce), a single, raised-cone, Belleville-style spring that encompasses the entire circumference of the pressure plate ring. The Borg & Beck style uses the wide fingers that apply pressure to three sets of coil springs located between the hat and the pressure ring. The Long style also uses three thinner fingers that actuate coil springs. The Long style is popular in drag racing because the coil spring height can be fine-tuned for stand height. Further centrifugal weight can be added to the clamp load by use of tiny washers added to the ends of the fingers. Adding weight to the end of the release fingers exerts additional centrifugal clamp load on the pressure plate based on engine speed.

heres a new Centerforce DYAD clutch Clutch comes complete with flywheel, drive disc, floater plate, floater disc, pressure plate, and all the necessary hardware for install. The assembly came completely balanced and was rated with a holding capacity over 1200 ft/lbs.








The Grumpy Grease Monkey mechanical engineer.
Staff member




theres been and will be many hundreds of thousands of the cast flywheels in use for many decades,they do not have the strength and durability of the steel billet versions, and do rarely fail, but they are rather remarkably durable especially if keep under 6000 rpm.
a lake-wood or similar, blow proof bell housing is good insurance


BTW the flat steel "TAN" in this picture, hard plate that is about 1/8" thick, that mounts between the flywheel and bell housing that helps protect the block from being damaged if the clutch or flywheel comes apart or loose at 6000 rpm
There are a lot of variables. 4.750 is the proper theoretic measurement from the face of the stud to the bell housing flange (contact surface with the back of the block). If you are using a block plate between the bell housing and block you have to figure this into the depth of the bell housing (add .132" and adjust the stud accordingly outward towards the block .132"). Flywheel thickness will also effect your geometry. A thinner flywheel moves the pressure plate away from the ideal contact point, as it moves forward the bearing and arm move forward, causing the outboard end of the fork to move rearward and cause increased pedal travel and effort. So the 4.750 measures to the back of the block because it is a constant measurement that never changes. It assumes you have a stock thickness flywheel. If the flywheel is thicker or thinner than stock you must also disl in the correct amount on the stud for this dimension. GM considers .960" as the "standard" flywheel thickness. So if your flywheel is .860 thick you need to move the stud forward another .100". Hopefully you are using a factory bell housing, because I don't know about McLeods, but Lakewood are almost impossible to get the geometry correct even with the adjustable stud.

GM has two stud lengths, 1.78 for the long throw out bearing and 1.48 for the short bearing which is what you should have. The Lakewood adjustable stud only provides up to 1.58 length. Barely enough to correct for the block plate and a resurfaced flywheel. The last Lakewood I worked with had .120 deeper than the stock bell housing to begin with, so proper geometry could never be achieved. If you get it correct with the clutch pedal pressed to the floor, the lower arm of your z bar that goes to the clutch will be pointing straight down. You never want it to go further rearward than that or you start stressing things with it going over center. It is okay for it to be slightly short of straight down towards the front of the car.

Good Luck! It can be terribly frustrating. I had the last trans in and out probably 7 or 8 times and never did get it right as long as I had the Lakewood on it.

many times clutch chatter is the result of an un-even flywheel surface, any decent machine shop can surface grind the existing friction surface a few thousands to correct that issue.
clutch chatter is the result of un-evenly applied clamping surfaces, usually a high spot(S) on the clutch pressure plate its housing or the flywheel surface, , but heat warping or a broken spring or mis-aligned spring will also cause this symptom.
if the clutch vibration does not go away once the clutch locks up,
you've more than likely,
got a drive line component alignment or rotation assembly or drive line balance issue.
you'll want to verify the flywheels mounted so its not wobbling, it may be warped, or the crank flange its mounted too has been bent or theres debris between the flywheel and crank flange, you,ll want too use a dial indicator mounted on the block and rotate the flywheel to find out, if the flywheel friction surface or outer diameter ,changes its distance from the block as it rotates




read ALL the links






















the c4 clutch is not that difficult to replace , do it correctly and replace the crap OEM parts with BILLET SFI flywheel and pressure plates and aftermarket disk, this gives the option of a larger 11" clutch, and a lakewood blow proof bell housing would not hurt
keep in mind the stock engines, never produced exceptionally high torque nor were the cars factory geared for max performance.

Chevrolet Corvette
The fourth Generation Corvette debuted in April 1983. With a new design, digital instrumentation, and a new interior, Corvettes sales doubled over the 1982 Corvettes.

Fourth Generation:

1983 Corvette:
None sold to the public

1984 Engine:
350 V8 205 HP

1985 Engine:
350 V8 230 HP

1986 Engine:
350 V8 230 HP

1987 Engine:
350 V8 240 HP

1988 Engines:
Coupe: 350 V8 245 HP
Convertible: 350 V8 240 HP

1989 Engines:
Coupe: 350 V8 245 HP
Convertible: 350 V8 240 HP

1990 Engines:
Coupe: 350 V8 250 HP
Convertible: 350 V8 245 HP
ZR-1: 350 V8 375 HP

1991 Engines:
Coupe: 350 V8 250 HP
Convertible: 350 V8 245 HP
ZR-1: 350 V8 375 HP

1992 Engines:
350 V8 300 HP
ZR-1: 350 V8 375 HP

1993 Engines:
350 V8 300 HP
ZR-1: 350 V8 405 HP

1994 Engines:
350 V8 300 HP
ZR-1: 350 V8 405 HP

1995 Engines:
350 V8 300 HP
ZR-1: 350 V8 405 HP

1996 Engines:
350 V8 300 HP
350 LT4 V8




Last edited:


The Grumpy Grease Monkey mechanical engineer.
Staff member
yeah its a truck, but it gives you some idea of why a blow resistant bell housing too protect your feet,
when a clutch fails may be an excellent investment, as it shredded the truck, and transmission








The Grumpy Grease Monkey mechanical engineer.
Staff member
Remember, that on this web site,
ignoring and skipping over links is rarely going ,
to help you in the longer term






http://www.ijrat.org/downloads/Vol-3/nov-2015/paper id-311201511.pdf

When a clutch engages with an engine, a pressure plate pushes a clutch disc onto the flywheel. This allows for the power of an engine to transfer to the rest of the machine.

This vital clutch disc makes sure that this engagement and disengagement of the flywheel happens smoothly every time. Early clutches were made with weak clutch discs that would wear out after just a minimal amount of usage. But today we have clutch material that can withstand high friction, high heat, and the force of the pressure plate.

In this article, we’ll run you through the best materials modern clutches are made with.

Organic clutch discs are made with a combination of friction materials. Most commonly, they’re made with phenolic resins, metallic powders, and compounded rubber. This type of material comes in two forms: woven and molded.

In woven organic clutch discs, fiberglass is woven into the discs, increasing their durability and longevity. This makes them superior to their molded counterparts even though molded discs are much more affordable.

Heavy-Duty Organic
Heavy-duty organic clutch materials are the same except they’re with a more significant percentage of metallic components. This means they’re more heat resistant. They can withstand temperatures as high as 700 degrees Fahrenheit.

However, when it comes to engagement smoothness, these clutch discs are identical to organic clutch discs.

Ceramic clutch plates are, ironically, made with a combination of copper, iron, bronze, and silicon and graphite. Because of their metallic content, these discs can withstand a lot of friction and heat. This makes them ideal for race cars and other high-speed vehicles that need to engage and disengage from fast-moving flywheels.

However, these discs are high-friction. This means that the engagement and disengagement of the clutch won’t always be very smooth.

Kevlar clutch discs have two key benefits: they’re incredibly durable, and they always engage the flywheel smoothly. They last 2-3 times longer than clutch discs made of organic materials.

These are the ideal choice for machines that require smooth, precise movement. Their only downside is that they have a long break-in period before they feel right.

Feramic is essentially a heavy-duty version of ceramic clutch discs. Made of similar materials – steel, silicon, graphite, etc. – feramic has an extremely high amount of friction, so they’re best used for machines that require quick lock-up like racing or heavy-duty trucking.

A subgroup of feramic clutch discs, carbotic clutch discs, are very commonly used in trucking because they have smoother engagement while retaining strong heat resistance.

Now That You Know About Different Clutch Materials…
You can make an informed decision the next time you buy a clutch for your car, truck, or any other type of machine that requires one. Just remember that there’s really no right answer when it comes to determining which clutch material is the best. It all depends on your financial situation and what type of machinery you need it for.
What is the Best Clutch Material for Friction?

  • Organic clutch discs are made with a combination of friction materials. ...
  • Ceramic clutch plates are, ironically, made with a combination of copper, iron, bronze, and silicon and graphite. ...
  • Kevlar clutch discs have two key benefits: they're incredibly durable, and they always engage the flywheel smoothly.