I finally got my car together after it has been sitting for almost a year. I took it out for a spin and the brakes are horrible. When I slam on the brakes going 10-15 MPH it takes about 3-5 seconds to come to a stop. When the car is in drive idling (5mph) and I slam on the brakes, it will just roll to a stop. The pedal feel is pretty loss too. I used to be able to lock up all 4 wheels. Also when I pull up the parking brake with the engine idling in drive it doesn’t do anything, it used to. Do you guys think I need to rebuild my rear calipers?

I know the brake booster is leaking vacuum, everything I press the pedal I can hear it. I am replacing that tomorrow. I replaced the master cylinder today with a rebuilt one and that didn’t help at all. I checked over all the brake lines and they are fine (when brakes are applied they do not flex at all). The brake rotors and pads are in good shape. I checked for air in the system by trying to bleed the brakes and found no air. Anyone have any ideas what’s wrong?

Also, the master cylinder on the car was steal, I just replaced it with a remanufactured aluminum one. Didn’t they stop putting steel master cylinders on thirdgens in like 84 or something?

I have a 89 IROC with 4 wheel disc and rear PBR calipers.

 

My brakes are doing the exact same thing, and I was also wondering if it was the booster. Although my parking brake does work somewhat. I've bleeded the system and checked all the lines - and nothing.

If you replace the booster, I'd like to know what happens. Anyone else have any ideas?

 

I replaced the brake booster today. It fixed the vacuum leak problem but the brakes are still horrible.

Anyone have any ideas? What are the signs of a bad proportioning valve?

 

i would just stick to the obvious stuff.. like fluid and pads


if you push the pedal all the way down and just don't get any friction.... then you need to do a couple things

flush your current brake fluid.. it's takes about 32ozs of new fluid to get a good flush... valvoline synthetic is very good fluid for the price.. like 5 bucks for 32oz's and it has a wet boiling point around 345degreesF

if that nets good pedal feel, then you're on the right track

if you still don't have enough pad friction to stop, then get some new pads... preferably some hawk brake pads

 

Good info prockbp, that is the fluid I am using. I am going to flush the whole system tomorrow.

Another though, I never bench bled the master cylinder before I put it on the car. I don’t have the fittings to do it. I just bled it with it on the car, that’s what the shop manual said to do. Do you really need to bench bleed the MC?

 

I had the exact same problem. No matter how hard I slammed on the brakes I couldn't get them to lock up and the car just coasted to a stop. Since I decided to never do brakes on my car again( especially the rears PITA) I took it to the dealer. They diagnosed it as a bad booster. After they replaced it and power bled the system it stops like an IROC should.

 

It is NOT possible to judge brake lines/hoses from the outside.
If they are still the original parts that came with the car,change them,you'll be surprised about the effects!
Also,in my case,it helped to go back to DOT 3 brake fluid,viscosity is different compared to modern brake fluids.
Good luck!