This is from a 1999 z24 convertible, 77k miles, pads are all new all the way around, rear brake adjustment is all the way down but the rears still brake exsively, it even drags the rear end down and sometimes to a slide, as if hitting the hand brake,

Im going to try a brake fluid flush, any DIY?

thanx in advance for any help!

how far do you have to yank the e-brake to get it to lock the wheels?

Check to see if you have brake fluid on the shoes, once contaminated,
they will grab like hell, just as you described.

have you ever adjusted the rear brakes sprocket adjuster?

also, i;ve seen one case on steve browns car where the part that the hard brake line attaches to the cylinder had rusted through so the cylinder shifted causing stuff inside to shift and make it brake harder and stick...

thanx guys, I think its the proportioning valve that went bad, where exactly would I find that?

ps. I really appreciate the help!!

RatZero wrote:Check to see if you have brake fluid on the shoes, once contaminated,
they will grab like hell, just as you described.

if contaminated, and they are new shoes, is there a fix or will I need new shoes?

Our proporioning valve doesn't cut the back down that much. Drums naturally brake less (under the same pressure) than disks. If memory serves me it's like 60/40 (f/b) nominal.

A blown proportioning valve would just make it 50/50, and the backs would still be less effective.

I second RatZero. Take some brake cleaner to those bad boys and see if that makes it any better (even if for a short time).

C.T.S wrote:Our proporioning valve doesn't cut the back down that much. Drums naturally brake less (under the same pressure) than disks. If memory serves me it's like 60/40 (f/b) nominal.

A blown proportioning valve would just make it 50/50, and the backs would still be less effective.

I second RatZero. Take some brake cleaner to those bad boys and see if that makes it any better (even if for a short time).

it made it better for a very short time after I cleaned with brake cleaner, now what? yo think it IS the proportioning Valve? or something else

does your car have abs? if so is it shot?

i know that when the ABS is disconnected or not worrking the rear tends to lock up more so than the front.

other than that i have no clue.

I had a 96 grad am with a bad Wheel cly and it did the same thing. Woud lock one wheel up. I think it is leaking fluid somewhere onto the brakes.



FU Tuning

I think John's got it, I think you're dripping (or spilled?) brake fluid (or some other oil) in the brake shoes. After the oil/slick effect burns off it will have saturated in to the shoes and makes them stick easily.

Check the brake cylinder, the lines, anything around there for even a small leak. You may need new shoes if this has been going on for a while. If it just started (less than 1 month) it will go away with use (after the problem is fixed).

Test the motion of the cylinder. With the drum off, have someone gently and slowly push the brake pedal to see if the cylinder moves slowly and smoothly. It should move outward easily and smoothly. If not, it's probably bad. Don't over-extend it; it's possible to damage it with no drum on.

Is the locking up inconstant (usually after you have been driving for a while), or does it do it from the second you hit the brakes in the morning? If it's inconstant you may have air in the lines cause weird reactions. Do you have ABS, Traction Control?

Traction Control can cause very weird problems. I does more than just control wheel slip. It also pumps up brakes pressure anytime the pedal goes more than 40% down. This will cause very weird problems if one brakes line has alot of air in it. Cause that line will absorb alot of pressure, so the TC system will pump up the system alot, causing other wheels to lock up, while the overall braking effect seems normal.

I had this problem with a Bonneville: On a bonne there are two lines that feed the brakes in a X fashion. One line was totally blown out, causing two wheels to have extremely little brake power, the other two got double the normal amount. Braking seemed normal at first. Than under stronger braking the two (left front and rear back) would suddenly lock up. ABS would totally freak cause TC was adding pressure, ABS was trying to relieve it. I didn't know what the hell was going on. I finally found the problem and fixed it.

Our cars have 4 lines, one for each brake. It's possible you're having similar problems. IF you have ABS + TC.

I would check everything very carefully for leaks, cracks, corrosion, etc first. Especially if you live in a norther region where the roads get salted in the winter.

mine does that every so often in the morning so what would it be in that case

sorry to thread jack

Do you park outside? Short daily drive? Could just be rust + brake dust buildup. Opening it up, cleaning it all good would fix the problem.

In general drum brakes suck and are prone to problems. I really wish GM would stop making them. Disk brakes cost very little more (especially when designed for and built on in the first place). And most people would not notice the cost difference, especially in the long run. They don't offer non-power rack and pinion, why still have drum brakes?

guess what ? after months of thinking about it and trying things the problem is ....


cheap aftermarket pads, got new GM pads and cars brakes fine... thanx