I just got done changing wheel bearings on my 98 z24. Went to test drive the car and as soon as you touch the brakes the rear tires lock up. I'm thinking somehow one of the wheel sensors got messed up. Can someone tell me if one of your wheel sensors isn't working, will the rear brakes instrantly lock up?

Forgot to add, i'm not getting any service codes or brake warning lights. Thanks!

A faulty wheel sensor will give you an ABS warning light. Did you replace the rear wheel bearings and if so, did you remove the brake shoes ? If you did remove the brake shoes - not necessary when changing rear wheel bearings - you might have got the leading and trailing shoes mixed up when you put them back.

The Cav uses what they call "servo assisted" rear brakes. It's a simple mechanical method that causes the brake shoes to ride up on the pivot point and wedge themselves hard against the brake drums when braking thus increasing their force. However, if things are not correctly set up this simple method can also be the source of many problems such as the brakes locking up.

If you have perhaps put the leading shoes back in the wrong position you will get the problems you have described. I cannot remember which is which but one shoe has a longer brake liner than the other.

Nope i only did front wheel bearings. I did not touch the rear brakes at all and everything worked before i did the wheel bearings.

That's strange...... Anyway because of the system the Cavalier uses for servo assist on the rear brakes locking up is very common. I would still investigate there. It may just be a coincidence that you had problems after working on the front wheel bearings.

Another thing is that the front wheel speed sensors are independent of the rear wheel sensors. If a front wheel sensor is bad it should not be locking up the rear wheels. I have the circuit in front of me and I see no connection other than all 4 sensors go into the ABS computer. Also, the ABS computer does not apply brakes but rather releases brake pressure to that wheel when it senses it locking up. The computer cannot apply brakes even if there is a bad sensor or for any other reason. So this is quite a puzzle.

damn i have to go to work i'll reply in the morning

Alright here's where i'm at. Just to eliminate the wheel sensors, i took the sensors off of my 2000 and tried it. Car still did the same thing. So i'm pretty much eliminating anything that has to do with abs.

Now what the car is doing. As soon as you touch the brake pedal the left rear tire locks up. Gradually more pressure, the right tire locks up as well. I'm talking locking up like your ripping the ebrake. I took both drums off and noticed the left brake adjuster was set way tighter than the right. So i backed off that adjuster. Tried the car. Right tire locks up first, then the left. Go figure. The brakes do not drag when you spin the wheels. Brakes work when you go on the brake pedal. E brake locks both wheels when applied. Releases both when takin off. Everything appears to be working fine with the back brakes. Just for fun, i put the front end up in the air and ran through a couple gears and tried the brakes. Just as i thought front brakes are working perfect. So i'm basicly clueless as to what's going on here. HELP!!!

Like I said, I think the so called, "servo assist" is causing the problem. This is where the brake shoes are by design allowed to cam up and wedge themselves hard against the drums to assist in braking when applying the brakes.

Wear and tear on the pivot surfaces of the brake shoes will cause those symptoms. How many miles have your rear brakes done? You might try to chamfer the leading and trailing edges of the brake shoes with a file to prevent them from grabbing. Sometimes that works. Also, your brake shoes might be contaminated with brake fluid or oil and that also tends to make them grab.

If it were my car I would get new brake shoes and clean the inside of the drums with fine sandpaper that is, if the drums are not badly worn in which case I would get new ones. I have bought new drums before and they were not very expensive.

Well today i sanded the pads and drums, and brake cleaned both rear brake assemblies. Drove the car around for maybe 15 minutes and everything was fine. Tonight i went to drive it and it was doing the same thing all over again. So i guess it's time to replace the pads. I'm not sure how many miles are on them, since i just got the car a couple of months ago. However there's pretty much on the pads yet. I just don't get it how they can be working fine one day, not the slightest hint of locking up. The next day both rear brakes lock up instantly. It just doesn't make sense to me.

I wouldn't feel bad about it because I know from experience what can happen with that type of brake setup. I am sure that new brake shoes and drums will fix the problem. Do one side at a time so that you can refer to an assembled system if you get stuck on how to reassemble the side you are working on. There are a lot of bits and pieces.

I just got back from talking to a buddy of mine who works as an auto mechanic. He said every j body that he has seen with other than gm pads in the back has problems with the brakes locking up. Especially when it's moist outside. He only runs gm pads on the j body's. He also said he used to put cheaper pads on and as soon as it would rain his phone would be ringing off the hook haha. So that answers it, new gm pads in the back and i should be set.

What makes the Cavalier rear brake system so sensitive to lockup with certain brake linings is because of its method of servo assist. I have fitted other than GM brake shoes with succes but I don't remeber what the brand name was. I used to buy them from Kragen in California.

Strictlycavyz24 wrote:I just got back from talking to a buddy of mine who works as an auto mechanic. He said every j body that he has seen with other than gm pads in the back has problems with the brakes locking up. Especially when it's moist outside. He only runs gm pads on the j body's. He also said he used to put cheaper pads on and as soon as it would rain his phone would be ringing off the hook haha. So that answers it, new gm pads in the back and i should be set.

Geesh, I've had this problem with the RR locking up intermittently for like the past 100K miles. I turned the drums, new shoes, even replaced all the hardware inside (springs, etc.) in there and never could get it fixed. I was starting to think I needed to replace the wheel speed sensors.

Now, I find out all I needed was to buy GM pads?!?

How are the GM pads different from the parts store cheapies?

If I recall GM pads are made in mexico.