When I first bought my vette, the brakes had to be pumped up several times in order to work correctly. I bled them twice, of which that worked for about a week or so, each time they were bled. Next, I removed and replaced the rear calipers, after I found that during a rebuild that the metal around the seals were pitted. Bled and again after a week or so, the brakes had air in them. I changed out the master cylinder, which seemed to fix my problem, but now 6 months later, I had a complete brake failure and luckily I was able to limp back home to the garage, which is where my 75 still is. There is NO external leaks, and I have a full reservoir. I have so far changed out the rear calipers and master cylinder. The only thing I haven't changed out is the front calipers. Is this a common problem with this year(s) vettes? Any idea of troubleshooting, without tearing into the whole system? You just can't drive around without brakes . If anyone else has ran into this problem, I really would like your help. Thanks in advance.


|UPDATED|11/25/2002 11:13:56 AM|/UPDATED|

It sounds like either your master cylinder failed or your brake booster. Do you have to push real hard to get them to work?
If so it is your booster. If not I would suspect the master cylinder or proportioning valve.
Good luck, Mark

That kind of makes sense, but what I am really confused about is that I just replaced the master clyinder. I know that even new parts fail, but the problem I am having is even worse than the original brake problem I was having. I think that replacing the master cyl isn't going to hurt. I will make sure that this time I get a top of the line replacement. As we know, we have GOT to stop from time to time. :)

|UPDATED|11/25/2002 11:15:45 AM|/UPDATED|

I know this may be a simple thing to ask, but are you bleeding the brake lines in the correct sequence? Both the Haynes and Chilton manuals list the bleeding sequence that I have used successfully (several times).

Also check your rotors. I have not experienced this (yet), but if the rotors aren't true they will cause the caliper pistons to move back and forth CREATING air in the brake lines (which leads to a soft pedal, which leads to no brakes). There are several references to this issue in other postings.

Good Luck...!!!

Mark my be on to something. You said a complete brake failure! Did you have a brake pedal or did it go to the floor? If you push hard on the pedal does the car at least slow? Could be the PowerVac. Its hard to have a complete brake failure with a daul MC, but it would be harder than .... to stop if no Vac or the booster failed. It would take extreme foot pressure to stop the car.

|UPDATED|11/17/2002 6:20:09 PM|/UPDATED|

A couple years ago I was on my way home while I was approaching a yellow light... pushed the brake down and it went right to the floor and I knew I wasn't stopping anytime soon, luckily nobody was ahead of me and I preceded through the light just as it turned red. Made it home and then when nobody was out I drove it very easily down the road to the shop. Its been a while, but I think it was my booster that went.

When you bleed the brakes, do you get a god high firm pedal or does it never pump up? If it does pump and act normal till you drive it, I would start looking for rotor run-out. mine would pump up fine and drive around town fine. When I ran it at higher speeds for even as little as five minutes, I would lose the brakes.....rotors all needed to be replaced.

Well, here is the update. I put the babe up on jack stands last night and I first gravity bled the brakes, which did nothing, the pedal still went to the floor. I next had my wife assist me with a pressure bleed and even pressure bleeding them would not help. If you pumped the pedal about 10 times, really fast and hold firm, you have some brakes, but if you let off, the pedal went back to the floor. Tonight, I'm stopping by and picking up a new master cylinder, which I think will fix the problem, if not, I'm out 82 bucks. The master cylinder I installed a few months back was a rebuild. The next one will be new and hopefully will last years, not months like the last one. I'll let you all know if this fixed the problem.



|UPDATED|11/25/2002 11:14:29 AM|/UPDATED|

I replaced my master cylinder and it did not help or fix the problem. I tried gravity bleeding, pressure bleeding and still NOTHING. You can get brake pressure when you pump the heck out of the brakes, but just as soon as you release the brakes and then reapply brake pressure, the brake pedal goes to the floor. My vette does not have power brakes. I can't understand how it looses pressure, but not having any external leakage at all.
I wonder if the proportioning valve would cause this.

Here is what I have found may be of help. First, the master cylinder is relatively bullet proof if you get a good quality rebuild. Be sure you bench bleed the master cylinder as shown in the installation instructions. I didn't do this once, and I went through a full quart of fluid trying to bleed it through the brake system.

If after you have bled the system and you get good pedal you may experience more loss of pedal after driving the car. If this happens there are some more things to do.

First, replace the bleeders. They will pit and corrode allowing air in but not fluid out.

If you still have a problem after driving the car a while then the problem is most likely run out of the rear bearings. The run out specs are rediculously tight. This is so the rear calipers, which don't float, won't pump air. The original design of the caliper piston uses a dust boot and flange or cup style seal. The cup/flange collapses when the internal pressure is lower than the external pressure allowing air in. Thus the air is "pumped" in. The cure is a bearing rebuild and adjustment costing $400-$800 depending on the shop to tighten up the run out. Another solution if run out is not excessive, but enough to cause pumping is a caliper that is available from one of the catalogs that uses "O-ring Technology". The O-ring prevents the pumping the cup type seal allows.

If you need help finding this you can let me know. I have a source for these and they are cheaper than the catalog guys.

Alex