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Pontiac GP - ongoing brake problem

This is a total mystery to me. Grand Prix 1991, 3.1L FI, disk brakes. The brake pedal is, and always was, very soft. On all other cars I owned or drove, the pedal travels about 1/4 to 1/3 of the way down and then I feel good resistance as the brake pads engage the rotors and stop the car. On this Pontiac, the brake pedal goes 1/2 to 2/3 of the way down before the brakes engage and I feel some resistance. I do quite a bit of maintenance myself, including brakes on all my cars. Here's what this Grand Prix got over the last 3 years:

- Replaced master cylinder twice.

- Completely flushed the brake fluid, refilled with new fluid, bled all wheels each time.

- New brake pads.

- 2 new calipers.

- Turned / shaved the rotors twice, replaced with new rotors when the old ones became too thin. None of this improved the brake pedal behavior. With the engine off, the pedal stays high, as expected. With the engine on, it behaves as described above, I.a. I believe the booster provides good power assist. a) What else can cause the pedals to behave like this, and how do I fix that ? b) Is this a common symptom on Pontiacs? Common to Grand Prix? Common to GM cars ?

Reply to
Gershon Shamay
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"Gershon Shamay" wrote

It sounds like you have a problem with the rear brake calipers. These vehicles had a lot of problems associated with the rear calipers and/or rear caliper adjustment procedures.

Your best bet would be to pull off the rear wheels, and check and see how far you can move the park brake levers before the rear brake pads stop the rear rotors from turning. If it's any more that about

1/2 - 3/4" movement...you need to manually adjust the rear discs. Simply move the park brake lever to the "engaged" position, hold the caliper piston in the "out" position with the tip of a screwdriver while bringing the park brake lever back to it's "off" position.

Try this first and see if this helps the pedal height.

Ian

Reply to
shiden_kai

Could be a bad "reaction disk" in the booster - that little segmented rubber "spring". I Tried to find an old enough manual around here to show the breakdown of the booster, but they've all, apparently, flown the coop.

Reply to
clare

This car has no park brake lever. It has a parking brake pedal which you must pump 2-3 times to engage the parking break. It does the job on my car, but there's no obvious way to measure whether it's too lose, too tight or just right.

The only part of the piston that is [barely] visible is its tip which pushes the brake pad metal backing. Are you suggesting I try to hold this round tip with a screwdriver so it won't retract into the caliper ? I'm curious to hear whether anyone else performed this adjustment successfully and how exactly they did it. I thought the caliper piston is self-adjusting over time, moving in more and more as the brake pad wears down.

Reply to
Gershon Shamay

My 94 Grand prix does not exhibit the problem you describe. If the brake pedal it 1/2 the way down, I've done stopped, and then some. I would look the vacuum booster ... make sure it's doing it's job (Sorry, I don't know how to test it)

Reply to
clevere

"Gershon Shamay" wrote

Sure it has a park brake lever...actually two of them...I was talking about the levers at the rear calipers.

I just told you how to do the adjustment. For the record...I've been a licensed technician for about 23 years....almost all those years in GM dealerships. I've performed that adjustment successfully literally hundreds of times. I've had to do it to Camaro/Firebirds, Riv's and Toronado's...W-bodies like yours...and some Fiero's. They all had similar type of rear brake setups. I can't tell you how many times that procedure has "fixed" a low brake pedal. Maybe it won't on your vehicle, but I try to go by what my experience tells me...as I can't see your vehicle in real life.

I'd show you some pictures of how to do it....but I don't happen to have any at the moment. My explanation will suffice, if you take into account that I'm talking about the "levers" at the rear calipers. By the way....yes...the pistons are "supposed" to be self adjusting over time, but they don't on these cars...except maybe when the car was brand new.

Ian

Reply to
shiden_kai

I had a regal (w-body) I pretty much gave up on the rear brakes. I even done what Ian had just explained but it only lasted for a short while. From what I heard elsewhere sometime back that once you had those rear rotors turned they never stay adjusted. This is probably true if they get a lot of wear. I dont know what the condition of the rotors are in question but if they arent new or if they are below specs perhaps new ones with new pads will help.

Reply to
Bon·ne·ville

Testing the vacuum booster is pretty easy .. Check Air Tightness

1.. Start the engine. 2.. Stop the engine after running for 1 or 2 minutes. 3.. Pump the brake pedal several times. If the pedal goes down deep the 1st time but gradually rises after the 2nd or 3rd times, it is in good condition. 4.. If there is no change in pedal height when depressed the 2nd and successive times, it is defective. Check Operation 1.. With the engine stopped, pump the brake pedal several times with the same pressure. Ensure that the pedal height does not change. (you will have to pump the brake pedal repeatedly to remove the vacuum reservoir) 2.. Start the engine while the brake pedal is depressed. If the pedal goes down slightly at this time, it is in good condition. If there is no active change in pedal height, it is defective. Check Air Tightness Under Load 1.. With the engine running, depress the brake pedal. Then stop the engine while keeping the brake pedal depressed. 2.. Hold depressed for 30 seconds. If the pedal height does not change, it is in good condition. If the pedal rises, it is defective. Hope that helps,

Brendan

Reply to
Brendan

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