Extreme brake fade during panic stops?!?!?

[Off Road SHO]

I've got a weird one on my 91 that has me baffled. During hard braking I lose all power to my brakes, it's like I lost all the vacuum. If I apply the brakes lightly or with medium pressure I get light or medium braking. If during a panic stop with the no-power situation I release the pedal and then re-apply light pressure, I get my power back. Weird huh?

Tom

 

[NJSHO]

I think the test for a bad brake booster is exactly what you described, ie. push down nothing, push down again power. I will look it up later on the ford cd if no one else can verify by then. You sure theres no air in your lines? Sometimes the first application of the pedal will compress the air trapped in the line (soft pedal), and the second touch will be harder since the air is already compressed.

 

[Black '93]

Bleed them suckers, then bleed the master cylinder if you can. I would check the ground wire for the brake booster too. Maybe corroded

 

[Racer X]

Bleed them suckers, then bleed the master cylinder if you can. I would check the ground wire for the brake booster too. Maybe corroded

Check the what? Maybe he should check his brake booster fluid too?

Tom, check the vacuum source for the booster to make sure it's unobstructed. If it's fine, then your booster is probably shot and needs replacing.

 

[SonicRiot]

Your master cylinder may be slowly leaking into the booster. Look at the pushrod and see if it's wet.

Often a leaking master cylinder will ultimaltely destroy a booster because it will soften the rubber inside until it tears.

 

[1993MTXSHO]

if your goign to bleed them get them power blead, my pedle feels much better after that sometimes air will just get stuck in the line

 

[Black '93]

Check the what? Maybe he should check his brake booster fluid too?

Tom, check the vacuum source for the booster to make sure it's unobstructed. If it's fine, then your booster is probably shot and needs replacing.

I meant the master cyl. cause it can leak into the booster sorry.

 

[SonicRiot]

A master cylinder should be the first component bled, if it's needed. His symptoms seems to coincide with fluid leaking past the lip seals in the master cylinder. Often times, when a mater cylinder leaks in such a way, the fluid collects in the booster. If caught quickly enough, the booster can be saved.

 

[SonicRiot]

Ooh! Ooh! Just thought of soemthing else...

does this happen when you induce ABS? Does the ABS even work?

 

[MADDOG11]

Check the what? Maybe he should check his brake booster fluid too?

Tom, check the vacuum source for the booster to make sure it's unobstructed. If it's fine, then your booster is probably shot and needs replacing.

I think what he's saying is what the **** does a ground wire have to with a hydraulic system? There is no electrical power to the booster or the master cyl.

As far as the brake fade during panic stops I would bet the master cyl is taking a dump. My 97 F-body did the same thing. Replaced the master and no more problem!

 

[Off Road SHO]

Found it! Or them to be more precise. When I put the new master cylinder in, I forgot to put the o-ring between the master cyl and vacuum diaphram back in. I also had some leaking vacuum hoses along the firewall.

Thanks for all of the suggestions.

Tom

 

[SonicRiot]

Excellent! Diagnostic Team SHOforum does it again!


...Or not.

Glad ya' fixed 'er up!

 

[Off Road SHO]

Found another! Vacuum hose came off the DFPE sensor mounted on the rear head.

It's nice to be King... er, I mean have brakes.

Tom