Not normal at all. I'd suspect a leak in the system somewhere, if you are loosing hydraulic pressure.

Squishy brake pedal?
Have to push the pedal far before they engage?


Brakes have so many different components that all need to be working right at the same time.

Id start by checking for leaks.

Leaks in the rear drum can be hard to spot, you may need to take the drum off to look for moisture on the inside of the drum.





Eric

PS: when you replaced your booster did you measure pushrod length in case that may have changed from old to new booster?

 

Hmmm. If you don't have fluid leaks, that sounds like fluid is getting past the seal in the master cylinder. Is it a new master cylinder?

 

Sounds like an internal leak in the master.

 

^^^^^ plus 3 on internal leak, had one doing the same thing. No external leaks but pedal fades away while holding pressure on it.

Dave

 

Master cylinder is doing what is called "bypassing."
It will only get worse. Replace with a new (not rebuilt)
master cylinder.

ex-Global West GM
1991-1995

 

Exactly what he said. This is precisely how my first 66 coupe got wrecked. Went to grab a foot full of brakes and had no pressure. Luckily at a relatively slow speed. But it's not something to trifle with.

 

I had the same problem with my Acura. It was the master cylinder. If it was a wheel cylinder or caliper you most likely would be losing fluid.

 

Thanks for all the quick replies.

I have checked the entire car for leaks and the master cylinder is does not seems to be loosing fluid. However the master cylinder I installed came from Advance Auto Parts but I can't remember if it was sold as a re-manufactured or new one.

Who do you all suggest I get a master cylinder from if I swap it?

thanks
jcs

 

Yes

 

If it's a stock set-up.... More Information for RAYBESTOS MC36251

 

A bad cylinder won't usually leak fluid. More likely that fluid is bypassing the internal seal between the reservoir and brake lines.

 

++++, Correct, bypassing in the bore between both cambers of master.

 

I'm confused. A bad (wheel cylinder) does leak fluid. Let's make it clear the discussion is strictly about master cylinder.

 

A bad wheel cylinder usually leaks fluid, while a bad master usually does not. Reason is because the only seals in a wheel cylinder are between the inner reservoir and outside air. In a master, there are multiple seals, with some between isolated high/low pressure areas that won't leak to the outside.

 

Since I know that I have no leaks at the wheels and the master cylinder I installed during my rebuild is a Cardone from advance auto parts, I am going to do another complete bleed of the brakes to make sure all the air is out of the lines. And if it's not any better, I will get one from Dan. I ordered all my power steering stuff from him during my rebuild and I was very happy with the quality of parts and customers service I received.

BTW, I did not bench bleed the master cylinder before installing it but I bled all the wheels using one of those hand pump bleeders.

thanks
jcs

 

One final test before removing the MC is to remove the lines from the output holes of the MC and block them with blanking bolts.

Press the pedal and hold for as long as you need to feel for fade/pedal drop. If the master cylinder has a bad bore, a scored bore, or leaking seals, it will be evident with only the master under pedal pressure.

No further proof needed after that test.

Good choice with Dan at Chockostang. Best in the business.

 

If you are sure you have no leaks rebuild the master cylinder.

 

Brake Fade fixed

I replaced the master cylinder and thanks for suggesting the bench bleeding method. I was done in under 45 minutes.

thanks
jcs

 

Fantastic, glad to hear it.


Eric