First time poster here, but I tried searching, a couple threads came close but nothing seemed to quite match exactly whats happening with my car so here's hoping someone has some ideas.
The car is a 2001 Sunfire with ABS and rear drum brakes, it was sold to me in february of this year safety certified, I was told at the time that the previous owner had had the rear brakes fixed in order to pass the safety. (Fix was done by the mechanic doing the safety cert.)

Whenever it rains or is very damp out and the car has been sitting for a few hours, when I first start the car and drive, every time I touch the brakes for the first several times the rear brakes completely lock up, the rear of the car dips sharply, and the brakes make a very loud and sudden clunk sound. As near as I can tell the problem is with both rear sides evenly, there doesn't seem to be any bias towards a particular side. Cruising at roughly 30 km/h and touching the brakes causes them to lock violently and make the noise, and its abrupt enough to chirp both rear tires. The problem disappears after a few minutes of driving and stopping, but last night reappeared after an hour of highway driving when I exited the highway, presumably because the brakes hadn't been engaged for that hour. I havn't yet had the wheels off to inspect anything, I'll be doing that tomorrow, for today I'm getting ready to leave for work so won't have time til tomorrow.
From other threads I've read that there can be problems with the wheel cylinders or with 'damp pads', meaning the pads absorb moisture, but for the cylinders at least, it seems strange to me that both sides should fail so evenly, shouldn't the problem bias more toward one side for a mechanical error like that? Also, I havn't gotten any ABS lights or other warning signs on the dash as I presume I should if it was an ABS issue.
I don't have alot of experience with these cars, I've driven nothing but Neons for the last several years, but apart from the ABS I assume there shouldn't be anything too surprising or drastically different when I get the wheels off the car.

Thanks in advance for any and all help

Rob, I have a 96 Cavalier that does the same thing after it sits for awhile, I've had the car since new, and after multiple dealer trips, when it was under warranty, was told that moisture builds up in the drums causing the brake shoes to get just damp enough that they BITE the drums until that moisture has evaporated. My car has 114,000 plus miles on it. other then scaring the crap out of you when the brakes do BITE down, I'm sure you have nothing to worry about. It's just your Sunfire saying HELLO. LOL

I would check to see if they are adjusted propery 1st. If they are, I would also look to make sure the shoes are installed correctly, down to lubricating the backing plate at the shoe contact surface.

The shoes are the same length, there is no primary or secondary shoes on the j-car, but this could still be an installation problem.

If the responce above has any truth to it, and not a dealer trying to get rid of an annoyance, make sure that there is a rubber plug in any holes in the backing plate, that may be letting moisture in. Your rear brakes should not be "saying hello" ever. I have had several j-cars with SIMILAR problems come through, and MOST of them were adjustment issues, a couple had some very interesting shoe installations though....

Thanks for the advice so far. Still havn't managed to find the time to get the wheels off the car (bad I know, potential brake problems should never be pushed onto the back burner).
Small update on the symptoms list: The same behavior described in my first post has continued, but its beginning to seem as though there might be a slight bias toward the driver's side rear, though both sides still do it. And I discovered that its completely impossible for me to recreate the problem if I'm in reverse. I tested in a parking lot after a full day's rain, and there's no problem at all in reverse. I go forward, touch brakes, and slam to a screeching halt, I put it in reverse, and there's no problem at all.
And a more important update, yesterday when I left home for work, after it had been raining all night, the brakes did their usual thing, and I thought little of it. 2 minutes down the road though, I began to slowly brake to a stop at a light, trying to avoid the lock-up, and it happened anyway, but this time it didn't release. I had to get out of traffic, so I dragged the back wheels 20 feet around the corner to where I could safely stop, ABS light was on. Turned car off, turned it back on, brakes still locked. Shifted into reverse, brakes immediately released. Slowly drove forward, touched brakes, slammed to a halt again, brakes stayed locked again, ABS light again, had to reverse to unlock it, again. Rinse and repeat upwards of 10 times over the next several minutes while I slowly made my way back home. (I live in a very small town, and at this point was in a subdivision with zero traffic, or I wouldn't have tried to make it and would have gotten it towed.) By the time I got back home however, the problem was gone, brakes were behaving properly and I was able to stop smoothly at any speed. I havn't dared to go far yet, will be checking the brakes in the next couple days since I'm now off until saturday and actually have the time.
I'll investigate for whats been mentioned in above posts, though it doesn't seem like this is an issue of the car saying "hello" to me, so much as a "holy !#$@@# no way am I driving today!"

I have this issue on my beater... it's very random. When it does occur it only happens right after I've started up the car and applied the brakes for the first few times. Rears lock up, ABS kicks in.... car shakes like a whore.

I had the brakes off 2 months ago, I have a leaking rear wheel cylinder. Also my shoes aren't so hot lol.

I plan to replace the leaking rear cylinder and install new shoes and drums in the next week or so... and I'll fully adjust the brakes.

Sounds to me like moisture is getiting in there and being burned off on the first few stops. Get the drums off and get a look.

-Chris-



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