Help! Blonde Needs Brakes

[kitty]

OK. I admit it! I am stumped, and so are a majority of mechanics I have asked for assistance. My 80 coup has been going through master cylinders like popcorn. After changing one out, the brake light comes on within 50 miles or less and stays on. I have the brakes bled, light goes off......within 50 miles or less it's back on...and we try another M cylinder.
I ignored the light last year (after the second M Cylinder replacement) and came off an interstate ramp at 80+ to discover NO BRAKES. Pedal went all the way to the floor, pulled up on the emergency handle....zip! :W
Managed to live through that one with some creative driving and last second prayer, but would rather not tempt fate again. Doing my own brakes is currently beyond me hnoes and I am trying not to get taken by a mechanic that "sees me coming a mile away." Any advice would be greatly appreciated. Has anyone else had to cope with this??? How did you fix it?? I really want to drive my car this summer AND live to tell about it......
Thanks!

 

[minifridge1138]

Give us all of the information you can.

Original Calipers?
Original brake lines?
What work have you done yourself?
What work have you paid for?
When you bleed the brakes, do you see bubbles?

I kind of doubt master cylinders since you've had several different ones and the problem comes back.

The more info, the better the advice.

Good Luck!

 

[tcolyer]

Kitty, I have had almost the same problem as you for the last 4 - 5 yrs. I stubble over a web site that finally helped me. http://www.idavette.net/hib/BBfHInet12.htm
In a nut shell have all your rotors turned and check your final run-out (less than 3thousands) then check caliper alignment and shim if needed. I did this to my brakes and they are now perfect for almost 2 months.

Do not take for granted that new rotors are true. And you may have to shim the hubs to get as little of overall rub-out.

Good luck

You can e-mail me if you would like to discuss
tcolyer012@comcast.net

 

[DRTH VTR]

I am no C3 expert. But it seems that I remember that some of these older calipers need to be resleeved. It has to do with air getting in the system at the caliper?? Is this true?

 

[tcolyer]

I am no C3 expert. But it seems that I remember that some of these older calipers need to be resleeved. It has to do with air getting in the system at the caliper?? Is this true?

Yes, they need to have SS sleeves, almost all replacements have sleeves. Also they suggest you use o-rings instead of factory style lip seal.

Kitty has your calipers been replaced?

 

[Vettehead Mikey]

I'll take the chance of being rude, and suggest that a lot of the advice above is not quite accurate and could make things worse while certainly wasting a lot of money.

Please don't take offence.

Swapping calipers, turning rotors, shimming calipers (?), new rotors etc. is all putting the cart before the horse. Without knowing the root cause of the problem, the OP might as well keep swapping master cylinders every 50 miles.

Kitty, the average mechanic is not equipped to handle the braking system on C2/C3 Corvettes and frequently makes a mess of it.

Best thing is to find a specialist in your area who really knows these cars. The first thing to do is find out which end of the car has the braking problem, front or rear. My guess is the rear, and I'll guess also that there will be excess runout found on one of the rotors.

Next will be finding the actual cause of the runout. If your rotors have been replaced, most likely the new rotor was not machined to match the hub- a common mistake.

If it's not the rotor, there may be excessive play in the wheel bearings due to wear.

In either case, the surface of the rotor 'wobbles' back and forth as you drive knocking the brake pads back into the caliper and unfortunatley sucking air inwards also. The result is low or no brake pedal and a nasty red light on the dash. Bleeding the brakes will make it go away- for about 50 miles or so.

Specialised tooling and procedures are required to fix things properly.

Let us know what you find out.

 

[petes74ttop]

Brake problem!

Hello Kitty, Tcolyer gave you the correct link and Vettehead Mikey gave you the right advise, find a Corvette specialist and check the run out. PG.

 

[tcolyer]

I'll take the chance of being rude, and suggest that a lot of the advice above is not quite accurate and could make things worse while certainly wasting a lot of money.

Please don't take offence.

Swapping calipers, turning rotors, shimming calipers (?), new rotors etc. is all putting the cart before the horse. Without knowing the root cause of the problem, the OP might as well keep swapping master cylinders every 50 miles.

Kitty, the average mechanic is not equipped to handle the braking system on C2/C3 Corvettes and frequently makes a mess of it.

Best thing is to find a specialist in your area who really knows these cars. The first thing to do is find out which end of the car has the braking problem, front or rear. My guess is the rear, and I'll guess also that there will be excess runout found on one of the rotors.

Next will be finding the actual cause of the runout. If your rotors have been replaced, most likely the new rotor was not machined to match the hub- a common mistake.

If it's not the rotor, there may be excessive play in the wheel bearings due to wear.

In either case, the surface of the rotor 'wobbles' back and forth as you drive knocking the brake pads back into the caliper and unfortunatley sucking air inwards also. The result is low or no brake pedal and a nasty red light on the dash. Bleeding the brakes will make it go away- for about 50 miles or so.

Specialised tooling and procedures are required to fix things properly.

Let us know what you find out.

No offense taken Mikey; you are correct that is why I gave Kitty the link. The problem will be calipers sucking air as you said. Finding the root cause is a long process, being rotors rotors to hubs and wheel bearings. And this is not to say it could be worn out calipers.

 

[LVMYVT76]

If the master cylinders are defective, are you getting them from the same place? They might have a rebuild problem. Like a seal in backwards? have heard of this before. Try a different parts company that has a different brand. It's just a thought, it's hard to repair a problem with defective new parts.

 

[6880 Mike]

...check your final run-out...

That's the ticket. Check run out on all four corners. Excessive run out will suck air and give you exactly the type of problems you have run into. It isn't the master cylinder.

 

[red70vette]

We all sympathize with you and your brake problem. There could any one of a number of reasons it is occurring and without doing some diagnostic checks we can be no more accurate than the mechanic who replaced the last 2 master cylinders.

The previous posters have the right idea. Check with your local chapter of the NCRS or a local Corvette club. You need to find a mechanic who knows Corvettes not one who is willing to learn while you pay to replace parts.

 

[Vettehead Mikey]

If the master cylinders are defective, are you getting them from the same place? They might have a rebuild problem. Like a seal in backwards? have heard of this before. Try a different parts company that has a different brand. It's just a thought, it's hard to repair a problem with defective new parts.

Again this is advice is inaccurate- a master with a seal in backwards would leak fluid externally into the booster. It would not be possible to even bleed the brakes without losing fluid.

These are car brakes guys- not different recipes for a BBQ. Safety first. This car should not be driven until it is fixed.

 

[tcolyer]

Once again Vettehead Mikey is correct "Safety first. This car should not be driven until it is fixed"

Find a Corvette mechanic that is familiar with rigid mounted calipers (most cars have floating calipers that will compensate for a small amount of rotor runout) The fixed calipers like on the C3 will not and will cause the piston to move in & out and suck air into the brake system. The O-ring calipers style is suppose to eliminate this but if the rotors have large amount of runout they will still suck air into the system. Here is another link to a Corvette fever article that tells about the fixed caliper and run out issues:

http://www.corvettefever.com/techarticles/corp_0604_chevrolet_corvette_c3_brake_upgrade/index.html


Hope these links I have sent you help.

 

[oceangal]

Wow Kitty I am glad you are okay, scary for sure! See if you can find a corvette club in your area and find a good mechanic as the others have suggested.

 

[tcolyer]

Kitty, any luck yet with your brakes, keep us informed.

 

[Hib Halverson]

The "brake warning light" comes on for two reasons.
1) The parking brake is applied
2) One end of the brake system, front or rear, has a leak. When the brake valve moves as a result of the pressure differential between front and rear when leak exists, it eventually hits a switch that turns the light on.

Without seeing this car, not reading anything in your first post indicating that a brake fluid leak was found at any of the brake calipers and reading that you bleed the system to solve the problem but then, 50 miles or so later, the brake light is on, again; I'm going to guess that the rear calipers and maybe even the front calipers are sucking air.

If the rear bearings have a lot of play, either due to excessive wear or improper maintenance, that will cause air leakage at the rear, no matter how much you bleed brakes or machine rotors. Thus, the rear is where I'd start.

For more info on this see the article on brake service on the Idaho Corvette site and which was listed in an earlier post.

Lastly, I'd say that any further master cylinder replacements are waste of time. If the service shop you take your car to is not familiar with the special needs of 65-82 brake service, I'd look for a new mechanic.

 

[TMPJoe]

replace the calipers period you will be chasing this forever

i had the exact same thing on my car last summer....

there was no visible leak but once we put the new calipers on the car was cured completely

 

[JohnZ]

replace the calipers period you will be chasing this forever

This very common and chronic '65-'82 problem isn't related to the calipers - it's caused by excessive lateral runout of the rotors and/or excessive axial rear bearing clearance, which causes "air-pumping" of air past the caliper piston seals.

 

[TMPJoe]

This very common and chronic '65-'82 problem isn't related to the calipers - it's caused by excessive lateral runout of the rotors and/or excessive axial rear bearing clearance, which causes "air-pumping" of air past the caliper piston seals.

sorry but i went that route and it was the calipers

it was aging seals and corrosion purely from age..

my rotors were fine.. whole new rear end when i rebuilt the car... and yes we set it up correctly with the new dana rear

if she has the original calipers there is almost NO way they are not sucking air

we will see.. if she can get someone to check it.... my bet is it still does it... when we got my rotors off the car and took them apart the pistons were a mess...

 

[Vettehead Mikey]

sorry but i went that route and it was the calipers

Possibly YOUR calipers were the cause- but it is inappropriate to suggest that this would be the root cause in all cases. Throwing parts at a safety related problem and hoping for the best is not a wise plan.

Having said that there's many examples of people installing 'new' calipers to address an air pumping issue (particularly the o-ring equipped style) only to find some time later that the issue returns.

Rotor runout must be eliminated, not masked.