Hi,

I have a 92 bonneville. We've had a lot of repairs done, and the front breaks are continually locking up while driving. At the same time, the brake pedal is rock hard, and in the upright position. They will usally release after a while, say 30 minutes to couple of hours.

Some background information on the repairs we have had done. This started with a lack of braking, the brakes lost pressure, and we took it to a dealer. (There were no prior problems with the brakes locking up). Dealer ran ABS tests, and this showed the ABS had problems (sensor, pump), but the reason for lost pressure was master cylinder, and rear brake seal. We had the dealer do the rear brake seal, which did not fix the lack of braking pressure. We then took car to PEP Boys to have master cylinder done.

PEP Boys did the master cylinder, and replaced the brake lines which they said were leaking. We now had normal brake pressure again, but after driving the front brakes locked up.

We went back to PEP Boys and they said the right front caliper was locking, and said we had to replace both calipers and the flex lines. We had that done - but the front brakes continued to intermittently lock up.

Back to PEP boys and they now say they think it is a problem with the ABS system. We disagreed, stating this happened after the master cylinder and lines were done, and the brakes never locked up before. PEP Boys says it might be the ABS pump, which is dowstream from the master cyclinder, and the ABS pump may be malfunctioning - but PEP Boys does not have the equipment to test it!

I already know the ABS system was not functioning from the earlier dealer tests, but to
eliminate ABS as a cause, I pulled the fuse for the ABS system. The front brake(*) continue to lock up. PEP Boys said to take car to a dealer and have them test it

I took it to the dealer, and they said the ABS pump was bad and causing the brakes to lock. The dealer put a new ABS pump in.

A few days later, the brakes start locking, with the brake pedal hard as a rock in the upright position again.

Back to PEP boys, and they put a 2nd Master Cylinder in. All seemed well for a few weeks, and the brakes locked again. So PEP boys put a 3rd master in, and again all was well for a week.

Now they are locked and the car is again at PEP boys. The manager says he will get a genuine GM master cylinder, and put that in.

Anyone have any tests or ideas as to fixing this problem?

Does the booster play a role in the dard brake pedal? I guess I don't see how the brakes locking and hard brake pedal in the upright position could exist at the same time. Seems like if the brakes are locked, the pedal should be down, or able to be pressed to the floor?

We are already out over $1,000 on all the repairs to date. This would be tolerable if the problem were fixed.

Thanks,
Matt

Welcome to Bonneville Club, Matt.

Don't know dink about ABS (except that it is very expensinve), but....

I read in the Car Talk column that a booster can fail in such a way as to cause the brakes to drag. It can be so light that the only way you notice it is that your pads wear out way too soon, or maybe in your case, a little faster.

In your case, it looks like it would be worth checking this out. I think a rebuilt booster is only about $100.

Good luck, and please let us know how it turns out.

Hello Bill,

Thanks for the warm welcome, and the tip about looking into the brake booster. I have talked to the mechanic, and he has said that can cause a stiff pedal, but shouldn't cause brakes to lock. (Maybe there are 2 problems, but could they keep occuring similtaneously!)

Where do I find the "Car Talk column" you mentioned? I looked on this board and couldn't see where that was? I'd like to see what else was posted on this subject.

Is replacing that a DIY type job?

Thanks, Matt

Car Talk is a sydicated newspaper column authored by Tom and Ray Magliozzi (sp?) These guys also have a pretty funny hour-long radio program that airs weekly on PBS. I think they have a web-site car-talk.com, but compared to Bonneville club, it is hardly worth your time.

Your mechanic may not know about this possibility. The thing is - the booster can fail so that the brakes are not completely released. You can change a booster yourself; the piping has enough "give" to allow you to simply unbolt the master cylinder, and pull it forward enough to work the booster off of the pedal clevis. At least that'* what it says in my '92 FSM. I checked here in town- a rebuilt booster for your car is $150.

While I have it open, let me list for you possible causes of "brakes drag" from the FSM:

brake pedal linkage interference or biinding
improperly adjusted master cylinder push rod.
weak or incorrect brake shoe retention springs.
improperly adjusted stop lamp switches
contaminated or improper brake fluid
power booster improperly assembled valving or damaged
missing or loose brake assembly attachments
incorrect rear brake adjustment
insufficient brake shoe guide lubricant
restricted brake fluid passage
improperly adjusted parking brake
sticking wheel cylinder or caliper piston
faulty proportioner valve
operator riding brake pedal

BTW, Matt, is it the front, rear or both that are locking up? And what, exactly do you mean by that? All by themselves, the brakes come on? Or... when you touch the brake pedal instead of gradually slowing, the brakes lock? Do they release completely after they lock? Are the rotors and/or drums hot after driving for a bit?

The answers to these can help us narrow down the problem.

Hello Bill, The car is my son'*, and according to him what happens is - he is driving along. without breaking, and the break pedal seems to push back up and at the same time the breaks lock up.

He thinks it is primarily the front breaks, but I have to admit I am not sure. I was at PEP boys once after this had happened and they had the car up on a hoist. I could not budge the front tires at all, and I could just barely move the back wheels if I really tried hard to spin them.

I also saw the front cylinders start to smoke one time when I was following him, when this was happening.

Thanks, Matt

OK, so it seems that all wheels are involved. That would make it less likely (I think) that a brake component specific to the front or rear alone would be the probable cause. If we eliminate the master cylinder push rod as not likely with new master cylinder, and restricted fluid passages with new hoses, and bad fluid as surely it has been bled with all these new components, and operator error since this happens by itself (Man, that'* scary!) that leaves:

brake pedal linkage interference or biinding
improperly adjusted stop lamp switches
power booster improperly assembled valving or damaged
faulty proportioner valve

While I've never heard of a booster going bad, anything is possible. I'll toss one off the hip here. Did he install an alarm or anything that might have been routed or hidden under the kick panel in this area? It'* out there...but if something is moving around it might cause an issue.

factory alarm intsalled

Ok...well that'* out of the way. Guess it'* more mechanical.

man im sorry to hear that u figured anything out yet?