POS 96 Cavalier rear vibes when braking

[joshs1ofakindxj]

Ok, lady friend is having problems with her cavalier. I'm going to look at it this Friday evening, see what I can do. She sent me this from her and her BF:

the problem most likely can be attributed to me banging the **** out of the drum to un seize it the first time I took it off to change rear pads...since then the back trailing pad on left wheel ate completely through in 3 or 4 months. there was a brand new drum on it and the surface finish looked good. when you spin the lugs with the wheel off on the back left wheel you can see that the whole wheel bearing assembly is out of round. should compare to other side to make sure it isnt an optical elusion.

However, when you brake at high speed....massive vibrations which feel like warped rotor (and may be). but, when you apply pressure to E-brake at high speed there is no vibration this means that maybe only back right wheel is grabbing when e-brake is applied or the problem may not be in the drums at all

The shaking is felt all around and the rear left tire locks up when the brakes are applied

I'm thinking rear left brakes installed wrong, bent hub, or bad hub, but I don't think it's an air pocket in the right rear line or something hydraulic.

I have an indicator I can set up on the brake backing plate and check the hub face and hub edge run-out. What is an acceptable amount of run-out?

Hopefully it's something simple like a brake adjuster is fully extended.

[DMG]

The locking up is a seperate issue on J bodies. Usually means the rear drums are worn oversize, the shoes are out of adjustment or both. Does the steering wheel shake you hit the brakes?

[joshs1ofakindxj]

She said "kind of"...I'll test drive it Friday and check it out. I didn't expect the best description of symptoms from her.

I also believe we're dealing with a new drum on the locking up brake, so I'll be suspect of the adjustment.

[88wd21]

agree with DMG, usually the lockup issue on those little GM fwd's equals to be an out of round drum and/or whacked adjustment. The shake makes me want to say front rotors though since it ain't there with the e-brake. It 'should' still give the shaking symptom if it were in the rear when using the e-brake from my experiences.

[DMG]

Front pads/rotors for that thing are really cheap and easy to do.

[joshs1ofakindxj]

Ok, what is an acceptable amount of run-out for the disc face? Thanks

[DixieJeeper]

around 0.0020 max but it varies from manufactuter and brake lay out..
I can look in my brake spec book tomorrow at work and let you know for sure on the cavvy

down and dirty way without a dial indicator.. take a sharpie. draw and number lines repsenting the numbers on a clock face radiating from the hub... take a micrometer and measure at each point... make yoru averages and your high and low and it will show a rough idea of how warpped it is.

[DixieJeeper]

1992-1997 Cavalier, Corsica, Beretta

Front Discs:
Maximum Parallel Variation; .0005 (measured as described above in multiple locations with micrometer)
Run out: .003
new thickness: .796
minimum machining/pad replacment thickness: .751
discard: .736

Rear Drums:
Run out:.006
New: 7.880
Maximum: 7.899
Discard over: 7.929

There you go Josh.

[joshs1ofakindxj]

Thanks. I have a dial indicator. I'm thrilled to finally have a use for it, other than gear backlash.

[DixieJeeper]

yea AND you won't stink of gear oil when you and the lady friend go out for dinner.

[joshs1ofakindxj]

Well, turned out it was simple. New pads and rotors in the front. Rear brakes seem fine. Previously they were locking up, so everything was replaced, and one shoe didn't last a week, but now everything seems fine, so I think they just got a bad new shoe.

[DixieJeeper]

glad to hear it was a simple fix... for once.