I have an 86 Iroc with rear disk brakes. Just replaced the front calipers and hoses because I had a bad hose on one side locking up a caliper. After working on those I noticed the rears felt weak so I jacked the car up and the rear brakes will not hold the rear tires at an idle. I pulled both calipers and the pistons are moving as much as a quarter inch when applying the brakes with the calipers off the wheel. I also adjusted the parking brake which wasn't working but now is. You can literally stand on the brake pedal as hard as you please and it will not stop the rear from turning (it slows it, but won't stop it) even though the pedal is hard and won't go to the floor. I bled the calipers on the rear as well and there is good flow. Any ideas?!?!?!

 

I'd bleed again, starting at rear pass, then rear driver, then frt pass, then frt driver - maybe you got a bubble up into the proportioning valve when doing the front brake job that hasn't bled all the way back to the rears yet.

 

Pull and release the parking brake 30+ times and see what happens--and check the following link for more info:

https://www.thirdgen.org/forums/brak...ke-adjust.html

JamesC

 

The rear brakes were not working before I did the front brake job so the problem wasn't caused by that, I have taken the E brake bracket off the backs of the calipers and adjusted them as instructed in the other thread, and
this fixed my parking brake that hasn't worked in years, but it hasn't done anything for my rear brakes when using my foot brake. They will apply, just not enough.

 

My guess would be the proportioning valve. Mine was the same way until I installed an adjustable valve. Now I can set it up any way I like. Other have used "1LE" valves I think with success.

 

Same thing here front brakes are good Rear brakes suck. New Master Cylinder,Booster,Wilwood prop valve maxed out new calipers rotors and pads and they still suck!Both My 69's brakes are better than these POS If you get yours fixed let me know

 

This is a partial quote from the link I posted above:

Q: Do my rear disc brakes need to be adjusted?

A: A technical service bulletin described this for early-mid '80s rear disk brakes. It seems that the rear disks in these cars would be adjusted by applying the emergency brake. When you pull the emergency brake lever up, the lever turns this little device called an actuator screw. This little screw type device is also on a ratchet, so that pulling the e-brake up, turns the screw. But letting go allows the ratchet part to function and set the pads at that time. So, using the emergency brake is mandatory for maintaining the rear disk setting on early model rear disk units.

Good luck.

JamesC

 

I agree with JamesC. You have to use the e-brake to keep the rear calipers adjusted. Pull it 20 times and see how your brakes are. With the wilwood valve I am able to dial in super rear bias. To the point where the rear brakes lock up on a normal stop.

 

Our car doesnt have E-brake and am running 95 Calipers and rotors on 9" rear How far do you have your wilwood prop valve turn to the right? and are you running a tee or gutted stock valve?

 

Well that changes things. I know nothing about the later PBR rear discs other than people say they work much better than the early iron calipers. As for my wilwood setup, I am using it after a gutted stock valve. I'm not sure where its set off hand, but its not close to either extreme IIRC.

 

Hmm mine is between master cylinder and gutted prop valve? I just bought a brake pressure gauge to see what psi i have at different locations. but our valve is fully to the right it helped a little but not near where it should be can only hold 2000 rpms on a 3800-4000 stall converter.

 

I wouldn't think that would change things much. How did you gut the valve?

 

pulled the plunger assembly out the front and used an allen plug? I was wondering though on the stock prop valves is the front brake portion and rear brake portion totally isolated or is the valve "open" front to back?

 

You ever fix this?

 

I had the same problem with my 85 T/A rear calipers after I replaced the calipers and pads on all four corners. I tried to adjust the calipers according to the GM service manual without success. I solved this by using a combination of standing on the brake pedal while applying the E-brake a number of times and applying the E-brake, then standing on the pedal, then release the E-brake. This is the only way I could get the brakes to adjust properly. Now my rear brakes and E-brake work perfectly.

 

Not looking for a response, just throwing in my experience.

I bought my car two years ago and my e-brake did not work. However the rear disc brakes were working, except in rain or cold weather they would make some bad rubbing noises. I replaced the rear disc calipers with some A1 Cardone 18-4164 ($67 ea + 20 core), added new brakes pads ($30) and had the rotors turned ($12.50 ea). I was going to buy new rotors, but my buddy at O'Reillys said he could not get them though they were listed on their site. Anyway, bled the calipers really well and drove it around braking many times. Finally, stopped the car and applied the e-brake. It worked like a champ. The car does not budge. Also, big difference in the brake pedal. Does not take much to stop the car.

My old calipers were a different story. The passenger side e-brake arm moved freely, but did not move the piston. The driver side e-brake arm was froze forward.

I guess we'll see what happens over time, but I'd say I am happy with the outcome.

 

I got rotors for my 84 S/E off the shelf at the local location of http://fastundercar.com/ every time I call they have the parts in stock I just called on a master cylinder and yup it is in stock, no auto part stores including acdelco have it in stock have to be ordered.