97 Pontiac Grand Am, rear wheel locking up...

[fuel tanker man]

I've just bought a 1997 Pontiac Grand Am. 105K miles... overall good condition, but rear brake (seems to be the left rear) wants to lock up when you brake it really hard.

I'm assuming an ABS problem, but I'm not sure. I knew about the problem prior to buying the car, but since the price was good, I decided to take it and work on the brakes.

I believe the rear brakes are drum brakes. The previous owner said he had a mechanic check the brake pads, drums, etc., and he found no problems (so he said).

Does anyone know how the ABS works on this car? Any other suggestions?

Thanks,

Dan

 

[tom slick]

I had an '87 grand prix with the same exact problem. I don't remember exactly what fixed it but IIRC it stopped locking up after I tool it apart and adjusted them properly.

 

[rpn453]

First, pop the drum cover off and check the shoes and drum mechanism. This is likely a mechanical problem, not an ABS problem. Most ABS systems can only keep a brake from locking up, they can't hold a brake in a locked position. I've seen this problem caused by riveted shoes wearing down to the rivets, forming grooves in the drum that caused even new shoes to hang up in there.

 

[fuel tanker man]

Thanks... I do plan on checking out the rear brake drums and shoes ASAP.

Dan

 

[mechtech2]

I don't think ABS works on drum brake on that car. Maybe on the front discs.
They are simple to yank and inspect. Oil or brake fluid can cause sticking and locking up. You'd think that it would slip, but it can work the other way. Worn or broken components, or mismatched ones [side to side]can cause this.
It may be a simple side to side adjustment - they stick and usually don't work as designed.
Make sure the shoes are lubed with grease on the little tabs they slide against. If they are heavily worn, they will stick and cause erratic operation.

 

[fuel tanker man]

Thanks... I'll try to get the thing apart this weekend and see what's up... I'll try to post and update when I get the chance.

Dan

 

[alreadygone]

Before you take it apart, go to your favorite parts outlet and get wheel cylinders and new shoes (can of brake cleaner be a good idea too). I'll bet my arse aginst 9 green walnuts you've got a cyl seeping just enough fluid to cause this. Often when leak first starts it'll be wheel oposite one grabbing that's wet, at first fluid acts as a LUBRICANT,keeping leaking brake from functioning. So brake that's NOT leaking continues to hold and seems to be grabbing!!!

Check 'em both, IF you don't need parts you can allways take them back.

Bob

 

[alanu]

yup sounds like weeping wheel cylinders. Another possibility is oversized/machined drums that are binding the shoes. OR some pinhead put the trailing shoe in the leading shoe location.

 

[theburner]

One possibility is that grease has leaked past the grease seal (that keeps the grease in the bearing cavity) and dropped down onto the shoes. I had this happen once. It will lock the wheel hard. When you get it apart look for any grease on the shoes.

 

[fuel tanker man]

I didn't get time to take apart both rear brake assemblies... but the left side (the one which was locking the most) was dry of brake fluid and grease, and the shoes were good. This really baffled me...

The parking brake cable is in good condition, and not too tight; plenty of slack... Drum and shoes did not appear to be glazed, but I sanded the surfaces anyway. The low speed grabbing problem persisted, however...

I searched around on the 'net and found a Pontiac Grand Am forum, and from what I've learned, this is a very common problem with the front disc/rear drum ABS system.

The brake computer engages the rear brakes first, with a slight delay for the front discs. This is because the discs are already nearly touching the rotors, but on drum brakes, the shoes are pulled away slightly from the drums. So the computer gives the drum brakes a "head start" or sorts...

I might still find a wet or greasy right/rear brake assembly. I'll take it apart today.

One guy who claims to have solved all such GM rear brake grabbing problems (again, presumably common to the disc/drum ABS systems) says he simply installs new rear brake shoes of high quality, and replaces the return springs.

I did notice that the return springs were not quite strong enough to retract the brake shoes quickly and completely. I don't know how this might cause the rear brakes to grab, however--unless the head start the computer is giving the rear brakes, coupled with the fact that they are already too close to the drums, could be doing it.

The front shoes seem fine, so the idea that the front brakes are not working doesn't seem plausible. (Someone on that Pontiac forum suggested this). It was also suggested that the sliders on the front brakes might need to be cleaned and lubed, but I cannot see how this would delay the deployment of the front brakes significantly enough to cause the rear brakes to grab.

Both rear wheels are grabbing, as I can see scuffing on both tires.

I drove the car at 60 mph on a deserted, rural road, and slammed on the brakes. I did this three or four times. Everything works fine, no grabbing or stopping problems. Doesn't pull left or right... The ABS system seems to be working fine...

I bled the front brakes (thinking some air in the front lines might make the front brake operation spongy, causing my problem)... but the brakes still occasionally grab.

I also had a mechanic advise me, and he bled the main booster at both valves. There was no air in the lines anywhere; all was good...

Again, the rear brakes grab at low speeds only, it seems. If you stop from any speed over about 25 mph you never notice the problem. I suppose this is because the front brakes are firmly engaged by the time the vehicle slows to a stop, if you brake from a higher speed. The grabbing problem really only happens when you're going very slow, such as when you've just pulled into the drive way, or when in a parking lot scenario.

I'll check the right side today and see if it's okay. I may go on and replace the return springs, and possibly the shoes as well, even though they are only about half worn down. Maybe that'll solve the problem...

Thanks for the advice, and the sympathy.

Dan

 

[cousincletus]

Has the car always done this? Doesn't seem to me like it was designed to do that. I would do a complete rear brake job. Replace the wheel cylinders (stuck wheel cylinders are the most likely cause of rear brake lockup), return springs, shoes (the short shoe goes to the front), turn drums. I always use the relined shoes from the parts store. They work as well as anything else.

 

[cousincletus]

Oops, I just saw where you bought the car recently.

 

[fuel tanker man]

Well... I did replace the brake shoes with Bendix OEM pads, and I also installed new springs...

And the problem is fixed!

I didn't do the wheel cylinders yet, but if the problem reoccurs I'll do that next.

I noticed that the previous owner had put new pads on the right side, along with new springs (they still had the paint on them)... but no new springs on the left.

The pads were not worn more than 20%... but the new pads and springs somehow solved the problem.

Thanks for all the help,

Dan

 

[alreadygone]

"I noticed that the previous owner had put new pads on the right side, along with new springs (they still had the paint on them)... but no new springs on the left."

This often occurs when something has come loose (spring ,hold down pin, self adjuster, break). Still betting there's a fluid leak,,,or whoever replaced brakes may have contaminated with grease or another lubricant.

Bob