murcos brake posts

[grumpyvette]

I found this post info else ware, and while I may not fully agree with every last minor detail mentioned , its well worth discussing the info he brings up here, and he certainly brings up several good points

I worked as a technical consultant for Bendix training technicians for a few years and hopefully this thread will help with some basic and a few more advanced diagnostics and repair procedures for those who want to work on their brakes. This is mostly for disc/drum systems but drum/drum systems use the same information.
Let's start with the basics...
First and most importantly - USE THE HIGHEST QUALITY PARTS YOU CAN AFFORD!!! These are your brakes, the number one safety feature of your car. If the car doesn't run, you won't die. If your brakes don't work, you can get killed or injured! Don't skimp on the brakes!
Brake fluid - You must replace it every 24K mile or once every other year, more if you live in really humid areas (like Florida) or if your car sits a lot in the winters. Brake fluid is similar to motor oil in that it is designed to encapsulate the moisture and sediment in brake systems but it only has so much capacity to do so. As it ages the boiling point drops, deposits collect, and problems start becoming more expensive to correct. Flush and bleed the brakes after every other oil change and you'll avoid 70% of common brake issues. I recommend DOT 4 fluid or Castrol LMA fluid (low moisture absorbtion) as it has a higher temperature rating and is less suceptible to breakdown in high-performance use.
Wheel cylinders - If you have drum brakes on your car and over 15K miles on them I will bet the wheel cylinders are either leaking or sticking. I'll also bet alot of folks here think they are supposed to leak and operate just fine like that. Tea, not so much... Wheel cylinders operate at far higher pressures than calipers just to open the return springs, much less stop the car. Peel back the dust boots on the ends and if you find any brake fluid at all (assembly grease is OK) go ahead and replace them, they're cheap! Often, wheel cylinders will blow their seal during a hard stop, squirt tiny amounts of fluid, then draw air into the lines when you release the pedal. This essentially renders rear drum brakes useless on a disc/drum car, overworking the fronts causing excessive heat, wear, and dramatically increased braking distances. It will also cause spongy brake pedals, more so on drum/drum cars. If you have the hardware off check to see if the cylinders move freely back and forth, about 1/4" of travel. If they stick, replace them, it's cheap insurance!
Hardware - Anytime you replace pads or shoes replace the caliper hardware and/or return springs as well. These items are cheap and allow the system components to slide and return properly. Worn caliper hardware will cause uneven pad wear from the leading-to-trailing ends. Worn return springs will cause heel-toe shoe wear (different wear in leading and trailing shoes).
Calipers - 70% of your braking power is right here and most of you will have the standard 78mm single piston GM mid-size caliper. These are a stout piece for around town driving and the large bore is fairly resistant to sediment binding when maintained properly. For high-performance use they are marginal at best but this is a maintenance and repair thread so lets fix what you have. The most common problem afflicting calipers is sediment bind due to poor maintenance. The heat cycling calipers go through is staggering and the large-bore calipers tend to "cook" the fluid under heavy use and flushing the fluid yearly is essential to keep these working well. Binding is diagnosed through the pads, look for uneven wear side-to-side, pitting (numerous small holes on the pad face), and scoring (the pads look like the surface of an old LP record). I would strongly recommend rebuilding the ones on your car before getting remans, no matter how cheap they are. Why? Your's have been in service recently, you know their history, and they haven't been sitting in a junkyard for who knows how long awaiting rebuild while exposed to the elements. It's also very inexpensive, about $5 per corner! You would probably be stunned if you opened a reman caliper for an older car. Many will have heavy corrosion pitting on the piston, scored bores, corrosion scarring, and heli-coiled line and bleeder threads. None of these conditions are acceptable your brakes shouldn't have these issues. I'll back this up later this month when I rebuild the calipers on my daily driver, they were "professionally" replaced just before I bought it in November and I bet they are needing complete replacement. Why? Because the shop didn't bleed the system (black fluid in the master cylinder) and the brakes are spongy... Oh, those "professionals"!!!

 

[grumpyvette]

We have covered the basics for maintenance and pad/shoe problems, lets get deeper...
The newest cars I've seen on this board are typically late 80's cars. A minimum of 25 years of wear, tear, some neglect, and just normal use can cause more difficult to diagnose problems in the hydraulics.
MASTER CYLINDER - The master cylinder is the most important part of your car!!! Think about it, it's true!
Look inside your master cylinder reservoir for a moment and look at the fluid. Does it look like apple cider, tea, or coffee? It should be a golden clear color. If it's slightly darker (like tea) it's time for a change. If it's really dark (like coffee) and there is sediment at the bottom (wet black film) you have extensive seal deterioration and need a new master cylinder, PERIOD!
How about green fluid? Never seen it? Ask a neighbor who owns a 3 year-old ford if you can see his master cylinder. If he's like 90% of people, it's the OEM fluid and I'm willing to bet it's green! Green fluid indicates the copper in the brake fluid has started turning acidic from excessive moisture and is eating the brake-line inner coating and corroding them from the inside out. Fords do it quickly but after a dozen years or so I'll bet some of our board member's cars have this too.
Getting back to the blackened fluid - That film is particulates from the seals coming apart. Most later model (after 1968) master cylinders are made up of;
2 pistons (primary & secondary)
2 chambers (primary & secondary)
2 primary seals (named for pressure sealing, not location)
2-3 secondary seals (used for separation and sealing)
2 springs (primary & secondary piston return)
and a housing and reservior
If one of the secondary seals goes bad you will still have a decent pedal but your brakes will wear one or the other end much faster than the other. You can usually identify this problem when opening a master cylinder cap and finding one chamber lower than normal and the other near overflowing. Replace the master cylinder.
If one of the primary seals is dead you will still have brakes but with a low pedal and little stopping power. Replace the master cylinder.
If one or both of the springs are losing tension the pedal will return slowly and drag the brakes after you release pressure. Replace the master cylinder.
Also, consider replacement if you have headers and more than 30K miles on your master cylinder. The extra heat will damage the springs (heat-stress) and seals (hardening) inside the master.
Proportioning/Combo valve - Disc/drum cars and those built after 1967 use a 3-function combination valve (proportioning valve, metering valve, and brakelight warning switch) and are prone to many of the same problems as the master.
The prop valve is an umbrella-shaped seal that ONLY REACTS AT PEAK SYSTEM PRESSUREs! It is designed to keep the rear-end from locking-up and is designed to close off the rear brakes at a specific pressure, allowing no additional pressure. The excess pressure is fed to the fronts.
The metering valve is designed to pressurize the rear brakes FIRST, under light pedal application, to promote more even braking. On drum brake cars it can hold up to 125 psi before allowing any fluid to the fronts, simply to overcome the force of the return springs and engage both front and rear brakes simultaniously. Disc/disc metering valves operate at lower pressures as it only takes about 3-5 psi to move a piston.
If EITHER of these valve fail or the springs are weakened, you will have excessive brake wear on one end of the car. Drum to disc rear conversion? CHANGE THE COMBINATION VALVE DURING THE CONVERSION or you will tear up your new rear brakes!
Headers + 30K miles? Is your combo valve close to the headers? Remember how springs and seals deteriorate when exposed to high heat? Replace your combo valve, it's worth it.
Got nasty fluid in the master? Guess what else needs replacement?!
Remember, gravity does it's thing with particulates too so when you find it in the master cylinder/prop valve you'll certainly find it in the calipers/wheel cylinders.

 

[grumpyvette]

I want to address another issue, specifically regarding adjustable prop valves. I've been blasted on tech boards and even in classrooms 1000 times for this but I'll stick to my guns... If your car is driven on the street, use an OEM prop valve.
I draw very distinct lines between street cars and race cars and build each according to the primary conditions they will be used. Varying loads, road conditions, tires, weather, and suspension wear are all realities the OEM valves will cover, even though it is heavily biased to the front. If you are having other problems with your brakes, particularly the rears, do not just slap on an APV to solve the issue! This is a band aid at best and flat out dangerous at worst! If you don't have the technical skill to diagnose and repair a problem, don't work on it until you've learned about it! Also, please don't jump to the next level and modify a brake system you know little to nothing about! If your rear calipers aren't working properly, fix them! I'm sure someone on this forum knows someone who has done the APV, set it up in perfect conditions to balance his pressures, then did some trail braking going into a corner in the rain and flown off the road a$$-end first. Problem is, they may not have lived to back me on this. I'm not trying to enflame anyone, I'm just saying go to a library and learn about the brakes before messing with them. Their are a lot of knowledgable folks on here, there are also those who should be banned from posting any advise on the brake board, and their are 1000's of professional mechanics who don't know squat about proper brake repair. Think I'm full of it? The first post in this thread contains more info than is covered in an ASE MASTER CERTIFICATION exam for brakes, all 25 questions of it. Think about that!!!! Good luck!!!

 

[grumpyvette]

Here is a special note about turning drums and rotors - You need to watch what your tech is doing when they turn your drums and rotors. First, make sure they (or you) mark the index position of the drum (mark the hole and stud that went through it - or rotor if you happen to be working with a late model that has separate rotor/hub). When the machine work is done put them back on at that same marked position as this will compensate for any run-out of the hub.
Watch when the tech puts the drum or rotor on the machine. If he just chucks it on there and starts setting up the cutter - STOP HIM, get your piece, and LEAVE! He doesn't know wtf he's doing and should be fired. A properly trained tech will test the run-out of the disc/drum and adjust the holding cups of the lathe many times, swapping the positions in quadrants each time. This also applies to integrated discs with integrated hubs like on most of the classic GM cars from the 60's through the 90's, make sure the tech adjusts the inserts that ride on the bearing cups. If you see him doing this for a few minutes and checking each adjustment go relax and have some coffee - you've got a well trained tech working with your parts! I have had brake techs with 20 years of experience fired for incompetence on the lathe. Just because someone has done something for 20+ years does not mean they've done it correctly!

 

[philly]

flush brake system every 24k miles? god damn... even the dealerships dont do it that often

 

[grumpyvette]

flush brake system every 24k miles? god damn... even the dealerships don,t do it that often

yeah! thats one area that caught my eye, also,i generally change my brake fluid out when I change disc brake pads and thats about every 30K-40K on the corvettes, (btw Ive found ceramic pads work rather well on the street) as does dot4 brake fluid on most street driven corvettes
but I see the point in that some brake fluid does tend to be hygroscopic
Definition of HYGROSCOPIC
1
: readily taking up and retaining moisture from any source


related info
viewtopic.php?f=71&t=1848&p=16080&hilit=brake+fluid#p16080

viewtopic.php?f=34&t=10061&p=39212&hilit=ceramic+pads#p39212

 

[87vette81big]

I read Grumpy.
That Dude Murcos is A Brake Nazzi.
He isn't that good.
Dial Indicate it in. what I do.

I passed my ASE Brake section 100% perfect score every time I have to renew Retest.
all 8 Test for Masters Certification always 98- 100% test scores.

 

[Murco]

Thanks for the invite, Grumpy.
The biggest reason for changing brake fluid regularly, and what makes brake fluid unique, is that, like you stated, it is hygroscopic - it agressively absorbs moisture. If you work with brakes regularly youl'll find that 90% of all hydraulic system damage is caused by moisture in the system. Yes, your system is sealed, but moisture gets in through the master cylinder gasket and even gets absorbed through the hoses. Humidity plays a huge part in that but even regular rainfall can add to this.

If you get some brake fluid on your hand you'll notice it burns a little and afterward your cuticles will dry out. Brake fluid sucks the moisture out of your skin and this is also how it strips paint, it sucks the binders out. Once you open a bottle of brake fluid dispose of what you don't use within a week, it absorbs moisture from humidity from just being opened. This is much more prevalent in Florida than it would be in Arizona, but it still a problem.

I know, you've never seen that anywhere in an American car owners manual. Iactually had to argue with a GM service writer when I asked that they do it on my wife's 2010 Malibu! "These newer cars have different shielding in their hoses so they don't need it as often." My response? "Do it anyway..."
Take a look in any European or Japanese owners manual, they will all say 24mo/24k miles and the Europeans actually test the fluid as part of their TMV annual inspections.
This is a pretty good explaination...
http://www.aa1car.com/library/bfluid.htm

 

[Murco]

That Dude Murcos is A Brake Nazzi.

Ha! Not the first time I've heard that one! lol

He isn't that good.
Dial Indicate it in. what I do.
I passed my ASE Brake section 100% perfect score every time I have to renew Retest.
all 8 Test for Masters Certification always 98- 100% test scores.

I'm not Moses coming down from the mountain, just a guy who spent a lot of years specifically working brake systems in both a shop owner capacity and as a technical consultant for the company that created hydraulic brake systems. I have also argued for a longer, more in depth ASE exam for years...

 

[87vette81big]

That Dude Murcos is A Brake Nazzi.

Ha! Not the first time I've heard that one! lol

He isn't that good.
Dial Indicate it in. what I do.
I passed my ASE Brake section 100% perfect score every time I have to renew Retest.
all 8 Test for Masters Certification always 98- 100% test scores.

I'm not Moses coming down from the mountain, just a guy who spent a lot of years specifically working brake systems in both a shop owner capacity and as a technical consultant for the company that created hydraulic brake systems. I have also argued for a longer, more in depth ASE exam for years...

Its OK .
I like Newcomers with Macho Attitude.
Not many around like Phil, Grumpy, Rick, Bob, & Me.
Welcome.

I hate that black shit in old brake fluid too.
Even if it takes 2 Quarts & 400-500 pumps of brake pedal with all bleeders openI am removing all.
Must be Crystal Yellow clear.

In the old days before my time, ASE's were all Essay answer questions.
I think its a nice idea .
Lots of trick questions on ASE Tests.
Mechanic A says....
Mechanic B Says this....

Why don't they Give out 24K Gold Foil Master Mechanics Certicates like they did in 1970's???
Cheepskates today.
Piece of paper.
Without that ASE Registation # your just a piece of paper only.

 

[bytor]

I did a brake system flush on my 87 Corvette a few months ago. With 47K on the car and based on the nastiness of the old fluid. I bet it was mostly the original fluid.

Here's what my old fluid looked like.....


I flushed the whole system using a Motive power bleeder 'dry'. I only used it to pressurize the system and refilled the master cylinder multiple being careful not to let it run dry. This method was a lot cleaner way to do it by not having the possibility of getting brake fluid everywhere when removing the pressure bleeder.