Its an 87 IROC with 4wd. So far I have replaced my front rotors, front and rear pads, front calipers, front brakelines, and master cylinder. I have run about four quarts of brake fluid through the whole thing. It isn't the rear calipers causing the problem. But I can barely do anything more than stop the car. I am almost ready to sell this thing I love it to death but I have replaced almost the entire brake system and I have gotten nothing from it. Oh, and its maing good vacuum and the pedal is not misadjusted. How to I figure out if my brake booster is bad?

 

Can you give more info on what the problem is other then just what you have replaced? How is the brake pedal feel? What exactly is wrong? When did the problem start or has it always been that way?

 

You can tell if a brake booster is bad because the pedal will be very very hard to push or it will make a hiss noise when you press the pedal.

 

I think my brake booster is bad now that you mention that. What type of stoping power would you experience?

 

The pedal is very spongy and it will go almost to the floor before it will really brake...

 

Sounds like there's air in the master cyl.

Did you "bench bleed" it before you put it on?

If there's air in there, you can run gallons of fluid through it after it's installed, and the air will still be there; because the line isn't at the highest point in the cyl itself. You have to bleed the master cyl with it held level.

 

1) A bad booster will not cause this condition. You either have a defective master cylinder ( even new ones can be bad ) or have air in the System.

2) How are you sure that it isn't the rear calipers that are causing the problem?

3) Check the prop valve as well. You could have caused it to over center when you bled the brakes.

I'm thinking that #1 is going to be your problem. Review your brake bleeding procedures. Bench bleed the MC, then bleed the outlet valves of the Prop valve. ( Just crack the lines to bleed ).

Start at the furthest brake line ( Right rear ), then left rear, right front left front. Make sure that you pump the pedal slowly when building pressure ( Bleeders closed of course ) before holding pressure to bleed. Fast pumping can aereate the fluid and you'll never get all of the air out.

Gravity bleed the system first. I also like to tap the calipers with a small hammer when bleeding. This will dislodge an air bubbles trapped in corners or clinging to a casting.

Good Luck.

 

How about the valve on the booster cannister

Edit..wont go to the floor quickly ,,much slower than a bad mastercylinder....wher is the booster connected ..carb? manifold?

 

Are you sure the calipers are installed correctly? I had a jeep come into the shop once, the owner installed new brakes/rotors calipers the works. He bleed a gallon through the system with no luck, after an hour of me bleeding with no luck ready to quit, one of the other mechanics noticed the calipers were installed backwards bleeders down, I should have caught that.

 

Funny you mentioned thgat. I was just talking to one of our shop mechanics today ( Greg )and he mentioned the same thing. An MGB that had a terrible brake pedal after having a major overhaul at a local British Leyland dealership.

Complete system replaced, Calipers, Wheel cylinders, M\Cyl, prop valve etc, etc. Factory got involved and even had their " Special Techs" flown in. Nothing worked.

Finally, in desparation, the owner called Greg and asked him if he could take a look at it as " Greg " was into restoring British cars. 5 seconds after removing a front wheel, Greg noticed that the bleeders were installed pointing down. The dealer had gotten the right hand and left hand calipers mixed up.....and EVERY BODY missed it. Sometimes the simplest things.......