Rear disc brakes ineffective
 

I put my car on the dyno a few days ago for an emission test, and I noticed that the rear brakes were totally ineffective at stopping the vehicle. Even bringing the car down from 15mph was hard. I had to put the car in neutral, slam on the brakes, and then just wait for it to slowly stop.

I do not drive the car that often. I had the rear rotors turned about 6 months ago, and put in new pads. Not sure what kind of pads they put in (and I no longer live in the same city) but could that be the problem?

BTW, the rear passenger caliper does seem to stick, since at almost any speed, the pads are against the rotor trying to stop the car.

I plan to replace the calipers, but it sucks trying to get the parking brake cable off. (I have replaced everything on the fronts - calipers, pads, and rotors).

Do you have the iron Delco Moraine calipers? There was a recall on these if the vehicle is equipped with a stick. If you have an auto, they weren't recalled. Those calipers are not one of GM's better designs. I have them on my 1985 (I don't know when they stopped using those, but that's why I ask. )


I'm replacing my iron calipers with PBRs.

If you have the single piston cast iron calipers (sometimes referred to as J65 brakes) from the mid 80's you probably have the problem parrydise7 mentioned. These calipers fail to self adjust as the brake pads wear causing the gap between the pads and rotor to increase. As the rear brake pads wear, this causes the brake pedal to sink lower and lower before the brakes activate to slow the car. Since the front brake calipers do not have this problem, the front brakes do most of the work and the rear calipers do alomst nothing.

The "recall kit" is the answer to this problem. I have the J65 4 wheel disc brakes on my 85 IROC. I finally installed the recall kit a few months ago. It makes a world of difference. The rear calipers actually work now.

Hmm...just noticed in your original post that you have a 91 Z. Maybe your problem lies somewhere else other than needing the recall kit. Tell us more about your rear brakes.

Maybe it is possible the driver before me had the calipers replaced, and whoever put on the new ones figured "early 90s, mid 80s, all calipers the same" and threw on some defective ones? Not sure.

But Ill have it on jacks in a few days, so I can just take some pics of what I have.

Car is going on jacks tomorrow.
But first, heres a pic of the rear rotor. For Petes sake they are always rusted. Probably because the pads arnt putting enough pressure on them?

The PBR and Delco Moraine calipers aren't interchangeable.

Can you post a photo of the caliper?

He'll have PBRs.

Pic

Do you service your calipers regularly, and do you ever use your parking brake?

When I bought the car a little over a year ago, it had no parking brake.

So I put one on.

And it was then just like it is now - VERY useless.

But I still try to use it anyway.

I have only serviced the front calipers (replaced them, the pads, and the rotors). The rears, only had the pads changed and the rotors turned. The calipers obviously have to have the parking brake takin off, which I cannot figure out how to take without disconnecting it futher towards the hand brake itself. I just havnt had the time to jack the car up enough to replace both the calipers as well as reach the parking brake cable to disconnect it.

I will probably do this soon though. Hopefully new calipers will do the trick, but I was mainly curious if anyone else was having the same problem I have (no rear brakes, basically).

As a side note, the passenger side drags - at any speed, "squeek squeek squeek squeek squeek ".

By "service" I mean have you ever lubed your calipers?

No, never knew that they needed to be (I have never worked on brakes until recently).

No more replies = no idea where to go from here, except replace them, i suppose.

I'd take them apart first and see if your calipers are actually seized. If they aren't, I'd clean and lubricate the slides and put it back together and see if there was any improvement.

I'm just finishing up rebuilding the rear calipers for my 89 GTA... I've never done brake work before either. Surprisingly, it was actually a pretty easy job!

if pbr's are pushed into the bore without being turned (with the gm tool kit thing) will they seize to work?

Very common problem...my rear PBRs aren't that great either. They weren't always that way; many years ago they worked fine. I've heard of people replacing master cylinders, combo valves, etc. in an effort to fix the rear brakes without success. I wonder if the problem is something more basic, like there is something about the rear brakes that makes them tricky to bleed. I recently bought a Pheonix V12 brake bleeder, so I'll see if that helps.

If I don't get resolution out of that, I have a Wilwood adjustable prop valve that I'll put in.