I am throwing this one out there as weirdo problem.

Car is 92 formula with 4 wheel disc brakes. Pedal has good feel to it, not spongy. weird part is car does not stop very well at all. Like from 50 mph I can slam on the brakes an maybe I will stop in football field length.

I checked the calipers and they are not frozen. moved freely.

I tried some of the brake booster tests I have seen here on the board... pump up the brakes and then start the car, the brake pedal should go down as vacuum assist takes over...check. does exactly that.

I checked the check valve on the booster. If I pull it out of the booster while the car is idling, the idle goes up.

At this point, I am not sure what else I can check. I am thinking of replacing the booster. Is there anything obvious that I am missing?

Thanks for any and all help.

 

How well does the e-brake grab or does it even work at all?

 

ebrake works fine

 

Are the brake pads glazed over?

 

Pulled the brakes apart the other night. Pads look fine. Rotors look a little glazed but that is probably from not getting the correct pressure and heat bulding up.

I realize glazed rotors will hamper stopping power, the question is how did they get glazed?

I bought the vacuum booster yesterday and will put it in tonight. I'll post results so people can learn from this.

Thanks

 

Do you want to do at this systematically or do you just want to throw parts at it?

1. What I would do first is plug the outlet of the master that feeds the rear brakes and install a brake pressure gauge on the outlet that feeds the front brakes. Start the car and press the brakes hard, have a helper note the maximum pressure. Also, hold the pedal down and make sure the pressure does not decrease with time.

If you see a solid 1000psi or more, then you are good, move to step 2.

If max pressure is less 1000psi but solid, take a look at your booster.

If max pressure decreases with time, you likely have an internal mastery cylinder leak from the front circuit seal.

2. Repeat with gauge on the outlet that feeds the rear brakes. If all is well with front and rear circuits, move to step 3.

3. Reconnect all lines and master cylinder and re-bleed. Install pressure gauge on each caliper and take note of everything in step 1. Rear pressure will be well less than 1000psi, but should be easily into the 100's of psi.

If you see a solid 1000psi or more, then you are good, move to next caliper.

If max pressure is less 1000psi but solid, take a look at your soft brake lines, they may be soft. This is very rare.

If max pressure is good but there is a delay to get to max pressure, you may have a partial blockage in your brake lines somewhere.

If the pressure doesn't move with the brake pedal, you may have a frozen caliper or a completely blocked brake line.

 

That is a systematic approach. I don't have a pressure gauge like at my disposal at the moment. Also, I have pulled all 4 calipers and they are not frozen. Pushed the piston back into the caliper with a c-clamp, reinstalled and then pressed the brakes...they all came back to position after depressing the pedal.

Not sure if this would eliminate the collapsed hose theory. If the hose had collapsed, wouldn't the other 3 calipers work properly and stop the car? Also if the hose was collapsed, would the piston come back out of the caliper after checking it?

 

Try this. On the rear calipers, there is a small adjusting screw(allen head). If this isn't adjusted correctly, it will cause the problem you are having. I had the same problem with my iroc. I replaced all pads, rebuilt the rear calipers, rebuilt 1 front caliper and replaced the other. Replaced all rubber hoses and still had a soft pedal that barely stopped the car. The adjusting screw is for the free travel adjustment for the e-brake. That's why I asked if it was working properly. If the adjusting screw isn't set right, you'll have the hydraulic portion of the rear calipers fighting against the e-brake portion of the rear calipers. Once I got mine set pretty close to the spec from gm, my e-brake handle only travels half way up the pull now and I have great brake pedal that stops the car on a dime. I still have to do the final adjustment though. If you try turning the adjusting screw, be careful so you don't strip out the allen head. Mine was seized and I had to use heat, a lot of penetrating and patience to get it moving again. This was easier to do since I had the caliper disassembled so I didn't melt seals and stuff.