I have a 92 corvette convertable with the following problem, front callipers seize after about two to three pumps of the pedal, and will release if I open the bleed valve, have replaced callipers and rotors to 13 inch c5 mod after the initial seizing problem with the oem brakes, new braided hoses as well, Master cylinder and booster were replaced about 2 years ago, hoping not a problem with the ABS / computer system behind drivers seat, no proportioning valve in system according to all documentation and research, stumped need help to figure this out, Keith

Check the pushrod on your brake booster. If it sticks out too far, it will not allow the fluid back into the reservoir. You should be able to adjust it by screwing it inwards. You have to pull the master cylinder off to get to it.

I assume you know it's normal for the pads to drag on the rotors. And it takes quite a bit of force to compress the caliper pistons by hand even on a working system.

Usually to me if you crack the bleeder screw and they release that means that the brake hose(s) are collapsing internally (brake hoses have two layers). A vacuum is created when you brake, the hose collapses, and fluid can't get back out. The bleeder screw allows that to happen.
A few other suggestions regarding the brakes - flush the fluid well, remove the hardware and inspect the pistons in the caliper as well as the seals, make sure the slide pins are free of rust/corrosion/dirt and are adequately lubricated with slide pin grease (I use sil-glyde). Also, what Kevin said about the booster rod. Remove the m/c from the front of the booster with the two nuts that hold it on and look at the booster. In the center, you will see a rod sticking out that pushes the m/c plunger in. You need the check the length (bend a piece of wire or use a small ruler) so that it doesn't contact the m/c plunger when it's reconnected.

Good luck,

Matthew

I agree with the brake lines that's probably the most common one and the caliper piston seizing is another ill bet it your master cylinder or rod length Ive used a small dab of grease on the end of the rod.
Bolt the master up take it off and see if the grease is the same as it was when you put it on there adjust the rod dab of grease bolt it up keep repeating this until you see the lest amount of change in the grease.
That's the way to get it closest to perfect.

Thanks for the reply,the initial problem started when I had the car stored for about 8 months, I cranked the car up and drove about 10 miles and noticed there was a heavy load on engine and trans on freeway, pulled into the first gas station and smoke was boiling from underneath car, both calipers were on fire and break hoses burnt into, no other damage luckily as I was able to extinguish the fire with water for cleaning windows, I subsequently trailered the car and brought it home where it sat for another 4 or 5 months, I purchase the C5 up grade, which came with new 13 inch rotors, calipers and braided ss brake hoses, installed all the hardware changed to c5 wheels, and still have the problem I had initially, lines flushed a number of times, In considering the master cylinder and the brake booster being the problem, wouldn't the back brakes also seize up if it was and issue of the m/c not returning back into position.

Thanks for the reply, I am considering the recomendation that the problem could be the m/c piston not returning to proper position due to the booster rod not allowing it to return to its proper position, but if that were the case wouldn't the back brake also have the same problem as the m/c piston would also be misalined to allow its fluid to return also. just an observation/ Keith

Thanks for the reply, I have a question before I start this angle of trouble shooting this problem, If the booster rod is not allowing the servo/piston of the m/c to reurn to its proper place, would it also be misallined for the back brakes to also function. Keith

Quote:

I would expect them too.

Here is some basic info on adjusting the rod length:

http://www.jegs.com/InstallationInstr ... 00/555/555-631010-116.pdf

Based on your previous post, I'm wondering if the fire didn't damage something else?

Also, when you got the C5 calipers, were they brand new, or used? Also, what type of stainless steel lines did you install? Are you sure they are the right ones for your vehicle? I still suspect that they are involved in this.

Matthew

Quote:

No, not necessarly, there's way more front bias in the m/c.
Even when you slam on the brakes with the stock setup, in good condition, the fronts will lock and the rears won't (that's one of the reasons Doug Rippie came up with a bias spring that puts more to the rear for kihk performance driving).
Putting the C5 kit on puts even more to the front.

Changing to the C5 kit has eliminated the hose/ caliper sticking,etc issue.

It really sounds more like a m/c, booster, linkage issue.

With the key off, can you lightly press the pedal and get 1/16th to 1/8th freeplay before the pedal has resistance?

It can also be a blocked vacuum passage in the booster, a broken return spring in the m/c or even a misadjusted brake light switck.

The front and rear don't necessarily close the reservior ports at the same time. I believe the rear is supposed to first, but not 100% sure.