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Rear brakes keep locking up

I have a 1995 Pontiac Firebird 3.4L V6 automatic with ABS brakes. When I drive the car between 5 to 10 miles, the right rear brakes begin to bind, eventually locking up the right rear wheel.

I changed the brake shoes, both drums, all springs, the piston at the top and greased the self-adjusting rod. Also I took off the master cylinder and cleaned out the reservoir (there was a lot of gunk in there). I also separated the reservoir from the master cylinder and cleaned the gunk from the inlet holes (there was a ton of slimy stuff in there). I then put it back together and did a ‘bench bleed’, mounted it back in the car and bled the brakes.

I was able to drive twice as far as I did before the bleeding but after 10 miles the issue returned.

I always notice a high pitch but not too noticeable squeak that begins about 2 miles before they lock up. I’m assuming it?s the beginning of the brakes beginning to push against the drums. When I apply push on the brakes (as I’m driving), the squeak stops but the squeak returns as I start driving again.

Next the brakes become really hard, almost as though the brake lines are full of pressure. When I stop at a stop light and take my foot off of the brakes, the car doesn’t roll forward at all. Then eventually the brakes lock up against the drums. The car must sit for about 45 minutes until the pressure is released and I’m able to drive it again. At that point, it is as though there was no issue at all, the brakes work perfect again until I get to the 5 to 10 mile range.

It seems to me that the brakes are building up pressure in the lines to the right rear brakes but it never releases that pressure. It seems as though every time I press the brakes, it keeps that pressure in the lines until the pressure is too high to allow for the drums to turn.

What could be causing this issue? Could it be that 'Proportioning valve? If so, does the 1995 firebird have one and where? I can’t seem to find it at parts stores.

Could it still be a bleeding issue? I successfully bleed the rear until the fluid ran clear but the front caliper bleeding valves on both sides were too stuck. I was unable to bleed those.

Could the ABS hydraulics cause this issue?

What could cause for only the right rear brake drum to lock up?

Any and all suggestions are appreciated.

Might be a problem of some sort with the auto-adjuster, ABS, proportioning valve or the parking brake mechanism, but my money would be on the brake hose connecting the brake cylinder to the brake lines. The inner lining of these hoses sometimes detaches when the hoses get elderly and blocks the hose. It doesn’t prevent braking because the pressures when the brakes are applied are pretty high. But it can prevent/delay the release of the brakes.

Are the shoes correctly installed? Is there a leading (shorter) and trailing (longer) shoe on each side of the car with the longer shoes towards the rear? Is The emergency brake cross-bar properly positioned between the shoes? Have you replaced the return springs and are those springs properly positioned and installed?

With the drum off, have someone GENTLY and slowly depress the brake pedal while you watch the shoes being pushed out against the springs. When the helper releases the brake pedal, do the shoes retract quickly and completely?? Look closely at the “good” side and see if you notice any difference from the problem side…

The next time it happens, pull off the road, jack up the tire and remove it and momentarily open the bleeder to see if hydraulic pressure is the culprit or is it a mechanical problem with the brakes…If you find no pressure (there should be none) then the brake has a mechanical problem…If brake fluid squirts out and the brake instantly releases, you have a hydraulic problem…The collapsed flex-line codger mentioned or a defective master cylinder that is not opening its relief ports… With ABS, each wheel has it’s own brake line coming from the ABS unit. You can disable the ABS by pulling its fuse for a while and see if that cures it…It will take a while for the ABS accumulator to bleed down so give that a few days to work…

I’m going to start with the most expensive and complicated possibilities first:

It’s possibly going to be in the ABS valve body and/or the proportioning valve (I don’t recall if these had both or not in '95) The ABS is valve body is not that complicated but does contain many small parts that have to come out and go back in a very specific manner but they are repairable at least to a point as often the problems are caused by crud or bad/leaking seals/o-rings … reguardless, I strongly suggest that problem be addressed by a pro-mechanic and depending on the shop rate vs. cost of a new/re-man ABS valve body will answer the question of it being cheaper to repair/clean or replace.

This vehicle may also have a front-rear proportioning valve as well as a load level propotioning valve. If either or both are locked-up, corroded or otherwise not workng correctly, this will cause the same symptoms.

If I’m reading your description of the gripes correctly, I honestly think you are dealing with a relatively minor and cheap repair and that being a wheel/axle hose. Brake hoses make the flexible connections between the hard lines and moving parts. The hoses are made in layers and when the layers delaminate, the inner liner of the hose can act like a check valve allowing pressure into the caliper/cylinder but not let it out which is what causes the brake to lock then take X amount of time before the fuild pressure can bleed off again.

First thing is to figure out if it’s a hose, caliper/cylinder, proportioning valve or the ABS valve that’s causing the problem. If it turns out to be a caliper/cylinder/hose, I’d strongly suggest just replacing all of them at the same time then you’re not back into again a few weeks from now when the next item fails.

Have you figured it out yet? I’m just curious as I’m going through the same exact problem with mine… What did you have to do? If you could email me at I’m going to change the brake line tomorrow so hopefully that works, but if you could let me know asap

I suspect a problem with the flexible brake hose on that corner of the car. Very common problem, and cheap and easy to replace. Due to the age of the car, you may consider replacing all the flexible brake hoses. The whole project would probably run you less than $100.