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Brake issues

Frank Z

Frank Z

NAXJA Forum User
Location
Colorado Springs
97 Dual Diaphragm Booster.
95 ZJ Prop Valve
95 ZJ Rear Calipers
76 Chevy Front Calipers (D44 front axle)

Bleed ports are all on top.

Bled my brakes yesterday (new front calipers installed) and had really bad pedal fade.

Today I replaced the Master Cylinder and bled the brakes again. RR, LR, RF, LF.

Still fades, same as previous M/C

M/C was bench bled prior to installing.

Already gone through a quart and a half of brake fluid bleding the brakes.

Any suggestions?
 
Thats not brake fade, which is basically your pads overheating.

Sounds like a leak. Maybe at the calipers? Does it do it when the engine is off too after you have pumped the pedal a few times to relieve vac from the booster?

It sounds like a bad MC, but you already replaced that.
 
My 89 does this.I put in 3 MC before i got it to stop.I don't know why it did it with the new ones but it did and now it is doing it again after about 1.5 years.
 
Frank Z said:
No leaks.
New M/C
Worse with the engine running
Click to expand...


Master cylinder internal leaks,

Propotioning valve internal leaks,

Break caliper leak although you should be able to see the fluid if the caliper/s were leaking.

There is no resaon for the pedal to go to the floor unless the fluid is going some where that it should not go.
 
NEW or REman master cylinder?

remans are junk IMPO.

2 other things I've seen do that is a bad prop valve, and a bad brake hose.
 
I've got another vacuum booster you are welcome to try. I'll throw it in the jeep for when I deliver the taillight.
 
Thanks Fred!
Can't hurt to try it, but I'd be amazed if that were the cause.

I'm really stumped on this one fellas.

No leaks, 3 M/C's, bled, bled, and re-bled.

Looked all over the place for a leak, can't find any.

Same thing still happens. Peddle slowly goes to the floor, even faster with the engine running.

I know some say prop. valve....but what is the internal failure? I can't seem to wrap my noggin' around that one.
 
Frank Z said:
I know some say prop. valve....but what is the internal failure? I can't seem to wrap my noggin' around that one.
Click to expand...

I can't either. I though if the internals wend bad it would possible join the two brake systems together.
 
Try pumping the pedal a lot ... all the way to the floor ... like 10 times, then check your fluid level in the MC. If it goes down, you have a leak somewhere, if not, you have a different problem. If your pedal gets firmer after a lot of pumping, then you need to bleed more.

Are your calipers seated properly ... is there anything that might be pulling your pads away from the rotors when you let up on the pedal? Too much travel would also cause the pedal to go to the floor.

Another question, has this combination of components worked in the past? Or did you just put them together and they aren't working?

I'm asking these questions to try to isolate the problem.
 
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