LT1 and a T56 in a 55 Chevy

You may be able to take as much as an inch from it since it is the pull type, but careful in doing so because it might not pivot correctly after so much has been taken off.
Yes to bore scope and small hole to watch as it pivots through its range to disengage the clutch.
 
Tried my hand at some calcs, hope I'm doing this correctly....

55HTclutch40s_Mar2019.JPG


Marked the fork end "A", the pivot "B", the rubbing point "C", and the slave cylinder at "D".
The ratio of 1.63" / 4.63" = 0.35, which means the closer to point B you get, the less the fork
moves toward the pressure plate housing, so 0.35 times the movement at point "D", 0.55"
gives a movement of 0.19" to contact at point "C", that is, the clearance at point "C" is only 0.19"
when the fork is not doing it's job.

Shortening the Tee stud to gain more clearance at point "C" is quite doable, but how much??
My slave cylinder at point "D" is capable of 1" of movement, plus I want clearance at point "C"
if point "D" is at full movement of 1". So, first let's see how much movement there will be at
point "C" if I can move point "D" a full one inch....

Using ratios, 1" of movement at 4.63" from "B" to find "x" at 1.63" from "B", or:
1/4.63 = x/1.63, or:
x=1.63(1/4.63) = 0.35"

Now to calc how much to shorten the Tee post at point "B", we need to consider the fork as
fixed at the release bearing, point "A", and calc ratios from there...
Since point "D" now has 0.55" movement before it hits, let's calc the additional it needs before it hits
for a full 1" of movement: 1" - 0.55" = 0.45" additional movement is needed,
figuring from point "A", 0.45"/8.38" = x/3.75", or:
x=3.75(0.45/8.38) = 0.20"
So if I shortened the Tee post by 0.20" I would have a full inch of movement
at point "D" where the fork would then hit the pressure plate.

Ok, if I shortened the Tee post at "B" to give 1.5" movement at "D", how much
would I have to shorten it??
First the additional movement needed at "D", 1.50" - 0.55" = 0.95"
Again, ratios: 0.95/8.38 = x/3.75
x = 3.75 (0.95/8.38) = 0.43"
That's a lot to take off of that Tee post !

1.5" movement at "D" will give how much movement at "C" to contact the pressue plate?
1.5"/4.63" = x/1.63"
x=1.63(1.5/4.63) = 0.53" at "C" to contact the pressure plate.

If the clearance at "C" is going to be zero with the shortened post at "B" and full 1.5" movement
at "D", what is the clearance at "C" with only 1" movement at "D" ??
0.5"/1.5" = x/0.53"
x = 0.53(0.5/1.5) = 0.18" clearance at point "C"

I do need to take a serious look at what other effects might come up if I shorten that Tee post 0.43" !!
 
I'm not sure you can bend cast iron, but if you can bend the fork a few degrees ...... Maybe you could do
both, bend a few degrees and also shorten the Tee stud. At best a delicate operation.

Just throwing out an idea, maybe it will prompt an idea on your part.
 
Diaphragm style pressure plates need .035 " clean release with the pedal down to the floor or the stop you have.
You do not want more than .045" release. Damage the pressure plate.
Checked with a feeler Guage between the Clutch disc and flywheel or pressure plate.
Free Air Gap on Full Clutch release.
You need an access window in the bellhousing to check Willy.
 
That's good info, I didn't have that before, did some more checking, came up with this below,
but if all I need is 0.035" to 0.045" movement at the release bearing, and I presently have
0.440" available at the release bearing before hitting the pressure plate with the clutch
release fork, it looks like I'm worrying about nothing. Plenty of clearance at the pressure
plate housing next to the clutch release fork with the bearing only moving max 0.045"...

And I need to rethink my hydraulic clutch release mechanism design!

I wrote this up before seeing your comment, it's interesting thinking, had fun doing it:

Took another look at the Tee Post mount, the fork, and the release bearing...
There is only 0.512" protruding out of the fork...
55HTclutch42s_Mar2019.JPG


And those side rails on the mounting stand are 0.191" high,
that leaves 0.321" available to cut, but I also need to allow room
for the fork to rocker back and forth, how much do you suppose that is?
I tried to measure it, came up with about 0.025",
so that leaves only 0.296" max that can be cut !!
55HTclutch43s_Mar2019.JPG


Had another thought though, let's check where the release bearing
sits on the tranny snout, I can measure that...
It turns out that the rear of the release bearing collar is
exactly flush with the rear edges of the bell housing...
55HTclutch44s_Mar2019.JPG


That means that the rear of the release bearing is also flush with the front
edge of the tranny, so with a straight edge I was able to measure just how
much travel the release bearing had available, turns out is is exactly 1/2" !!
55HTclutch45s_Mar2019.JPG


Using the same ratios that I used above, 0.55" movement at point "D"
gives 0.44" at point "A" (the release bearing), but we
want 0.50" movement at the release bearing (point "A")
which requires 0.62" of travel at the slave cylinder (point "D")
Since I already have 0.55" travel available at point "D", I just need to
add 0.07" to get 0.62" movement at "D", getting 0.50" at the release bearing.
In order to get this, I only need to trim the tee post by 0.030"
But I'd be touching the pressure plate housing, so I need to add
additional clearance for the pressure plate...

I ran the numbers several times, and came up with these results:
Trim the tee post 0.080" gives 0.070" clearance,
Trim the tee post 0.100" gives 0.100" clearance,
Trim the tee post 0.150" gives 0.170" clearance,

It looks like all of these trim options will not cause other problems,
taking into account the angular movement of the fork on the tee post,
the amount of post exposed under the fork, and the amount of the tee post
required to fit into that base mount on the tranny, I have about 0.296"
available for a maximum trim job before I might run into a functional interference.

So, the real question is, just how much clearance do I really
need for the pressure plate housing ??
My feeling at this point is to trim the tee post 0.100" and see if I can live
with 0.100" clearance at the pressure plate housing...
 
Diaphragm style pressure plates need .035 " clean release with the pedal down to the floor or the stop you have.
You do not want more than .045" release. Damage the pressure plate.
Checked with a feeler Guage between the Clutch disc and flywheel or pressure plate.
Free Air Gap on Full Clutch release.
You need an access window in the bellhousing to check Willy.

Now I need to find out how much release bearing movement on the tranny snout is required to get an air gap of 0.035" to 0.045" at the pressure plate/clutch disk ?
I submitted a request via email to Centerforce about this, let's see how they respond.
 
Now I need to find out how much release bearing movement on the tranny snout is required to get an air gap of 0.035" to 0.045" at the pressure plate/clutch disk ?
I submitted a request via email to Centerforce about this, let's see how they respond.
Thinking Willy....
I went through a similar headache on my old 70 TA a long time ago.
Mcleod Billet Steel Flywheel, Mcleod Pontiac V8 Scattershield with a block protector plate.
Supplied adjustable pivot ball too short.
Had to use a Pontiac V8 Early TA throwout fork.
Chevy V8 Fork Geometry ratio was all wrong.

Ratios got through College. Studied electronics my major. When I forgot a formula I used ratios like You.

Ended up making my own Pivot Ball. 1 .00 " inch taller.
Centerforce Daul friction clutch too 11.00".
 
Allright.
What I think happened is the Billet steel flywheel I see.
Looks like at least a 30lb unit maybe a 40lb.
Its Thicker taller than stock.
Despite the surface rust I can tell its a high quality Billet Steel 8620 part.
 
Grind the The T-stud to clear Willy. How much does not matter.
You can calculate on paper exact but what may happen you may end up in error yet because parts move around under pressure operation.
Flexing some likely to happen in the clutch fork & pivot T stud stand.

What needs to be done yet since the T56 uses an external slave cylinder is to make the Pushrod adjustable. Much like all Chevy & Pontiac vintage musclecars had.
That way you can dial in exact the correct pressure plate to clutch disc air gap release needed.
 
I'm essentially a mechanical engineer, from UC Davis in the early 60's, but trained and worked in farm machinery design, fabrication, and operation; hot rods is just a hobby, like my Dad and 2 of his brothers. I'm thinking that the hydraulics of the master cylinder and the slave cylinder will self adjust, and taking off that 0.150" from the tee post will not hurt anything, and will guarantee clearances, but I am thinking about your comment on the adjustable slave pushrod, might be a smart thing to do...

Yes it's the 11" dual friction setup, I've had good luck with those in other rigs, although my 650 hp blown Olds 425 powered '55 chevy gasser rips 'em apart (w slicks at the drag strip), had to go to a dual disk setup to get one that would hold up in that rig !! This rebuilt LT1 is bored and stroked to 396 and dyno'd at about 500 hp, so wanted a stout clutch. It's going to be strictly street, street tires, so I think that T56 will hold up if I don't get too nuts with it !!
 
Love all the numbers and calculations, it's wonderful when they add some
guidance to solving the problem !!!
 
With the shortened tee post, I had to shorten the mounting bolt an equal amount, it was too long...
But the tee post and fork went back together nicely on the front of the tranny, no problems...
Put the tranny back in the car, the fork "popped" back into position nicely on the release bearing,
and I was able to get a measurement at this end of that fork...
Was able to get a pic, difficult to do under there...

This photo is misleading, the end of the fork actually now sits slightly above the surrounding metal...
55HTclutch46s_Mar2019.JPG


This pic shows the full movement of the clutch release bearing on the other end,
I measured 0.800" total movement at this end, and was able to determine
that there was plenty of clearance at the pressure plate housing....
I bent a heavy piece of wire and hooked it up in there under the fork, between the fork and
the pressure plate, and felt around a bit, when the fork was fully depressed, felt like plenty of clearance...
55HTclutch47s_Mar2019.JPG


I still need to cut an inspection hole in the clutch cover, haven't made up my mind yet where and how big to make it....
 
Above or just beside the pivot ball and you will be able to see it in action and all the way to the T/O bearing.
 
Haven't decided what to do about an inspection window yet, still mulling that over....

In the meantime, had to check out just where the clutch slave cylinder
will sit with the adjustments I've made to the clutch fork support setup....

Removed the support piece that goes between the cylinder
and the clutch housing, and mounted the slave cylinder
with the piston completely compressed inside the cylinder...

55HTclutch49s_Mar2019.JPG


Measured this distance between the clutch housing and the cylinder, 1.643"...
55HTclutch48as_Mar2019.JPG


Reassembled it with the support piece, which is 2.000" wide,
which gives me 0.357" of piston travel behind the
open cylinder still available behind the piston...
55HTclutch50s_Mar2019.JPG


With a total stroke in the slave cylinder of 1.5",
and a max clutch fork movement of 0.80"
(probably less) I should be good to go with this setup!
 
having you post pictures like that makes getting a grasp on your project FAR EASIER
 
You have to measure the actual clutch disc air gap release with a feeler guage.
.035-..040".
Inspection window at 12' O clock or 6'O clock.
Pro Stock at 12.
Old School scattershiels at 6'oclock like the McLeod Pontiac V8 I use.
1.000 " hole provided to check.
 
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