This could be related to not bleeding the brake lines properly.... But, I changed out the: brakes, calipers, rotors all around on my 85GT.

before I did this I had a very soft brake pedal. hoping that the changes would make a difference, I have found that the brake pedal is still soft.

I don't see anything leaking, so how can I check to see if the Brake Master cylinder is good or possibly the booster?

oh yeah, if i pump the brakes a few times, the pressure to the pedal does get a little bit better, but not very much.

If the booster is failing, the brake pedal feel will be very stiff. So I doubt that's your problem.

One tell-tale sign of a failing brake master cylinder is "leak-down" of pressure. Press the brake pedal and keep constant pressure on it. If the pedal slowly sinks to the floor (and there isn't any brake fluid leaking anywhere), then chances are the seals inside the master cylinder have failed.

Another possible source for a spongy brake pedal is degradation of the rubber hoses leading to the brake calipers. Take a good look at them. If the rubber looks dry-rotted, it needs to be replaced. When the rubber in those hoses deteriorates, it allows the hose to expand when pressure is applied to the hydraulic system. That makes the brake pedal feel rubbery.

You should also double-check to make sure the hydraulic system is free of air.

[This message has been edited by Blacktree (edited 06-03-2009).]

Could also be improper adjustment/non working parking brake.

thanks, I did change the brake hoses on the back, but not the front. I will give that a try.

I had a shop do the back brakes so will take it back to them as well. I found a post about adjusting the rear calipers as there appears to be a very specific way to do it.

I will also check the brake pedal and see what happens.

Cheers,

Hello

I just went through brake master learning experience that you might benefit from.

In two cars we were having a soft pedal accompanied by a “booster hiss”, the classic symptom of a partial hydraulic failure or big air bubble but I was sure that it was neither. This began right after they both cars got a routine brake fluid change. This is not a new or unfamiliar procedure but it is the first time it’s had any adverse effects.

Our bleeding procedure used full pedal strokes.
As it turned out…one can destroy a working master cylinder by moving the pistons farther than they’re “normal” distance. A new one will survive but an “old” one can have its rubber parts destroyed.


We have now reverted to a vacuum bleeding technique that we used to use. It is a homemade canister made of PVC pipe. One tube connects the top of the canister to a vacuum pump and the other tube goes from the bottom of the canister to the bleeder nipple. It simply sucks fluid from the master cylinder through the caliper.

I’ll do a drawing if anyone wants one.

Yellow

Thanks,

A diagram would be appreciated.