I'm 99% sure the issue is a bad master cylinder, but I wouldn't mind some affirmation.

Brake pedal is just about nonexistant. Opened the bleeder from the front of the cylinder and pushed the brakes - got some fluid out of it. Opened the bleeder at the front wheels, got some fluid out of it. In both cases it wasn't throughout the travel, just at the very bottom where you would feel some resistance. The rears were even worse. No fluid came out from the bleeder, at the cylinder or wheel. With the bleeder open on the rear, the front would actually squirt upward from the reservoir.

I would also note that it looked like fluid had leaked out and damaged paint around it, but I didn't observe any leakage while I had it.

It seems like all signs point toward a bad master cylinder, but before I grab one I just want to make sure I'm on the right track before I go throwing parts at it.

 

Are the brakes adjusted and bled properly?

 

As Oldcutlass mentioned your brakes need to be set up properly prior to diagnosing a master cylinder problem. You brake pedal may very well be past the fun pedal if not set up properly.
If you have no leak in the system and the pedal goes to the floor then yes its a master cylinder.
As Oldcutlass also mentioned be sure you are bleeding the system correctly, fluid will spirt up out of the master with the cap off. Not sure why you are pumping the pedal with the cap off.
Let us know how you began and continue to bleed the system maybe we can help you further diagnose.

 

The brakes were adjusted properly. I don't think air/bleeding was an issue. I was getting fluid from the bleeder at the front wheel cylinders (at least a little) with no bubbles, and it was easily pushing it from the front master cylinder bleeder. The rear would seep fluid with the bleeder on the wheel cylinders open, but wouldn't push it out with pedal movement. It also didn't push any out from the rear master cylinder bleeder.


The car is a new purchase so I don't have much history to it. I was told it was probably a bad master cylinder. Yesterday I pulled the drums to inspect them. I adjusted the brakes to be just snug against the drum when re-installing. The fronts could use replacement and the rears are just fine as far as material goes.


Following that I bled them at the wheel cylinders, finding some fluid was making its way to the fronts (albeit very little, and only at the end of travel), and that it was doing the same from the master cylinder itself. I moved to the rears and repeated the process. No fluid coming out the bleeders of the rear cylinders, and no fluid coming out of the master cylinder to the rears. I don't suspect any leaks as I did not see any, and with the bleeders closed I do not lose any fluid.

 

If your master is full of fluid and you pump the brakes it should pressurise the system. Now if you pedal still seems very spungy with the master full and no leaks throughout the system then I would go ahead with replacing the master cylinder as you suspected. I would be sure to bench bleed the new unit well prior to installing. Let us know how it worked out.
Eric

 

Yeah it's well beyond "spongey," it's "absolutely nothing down the floor." And using the bleeders on the side, as if bench bleeding, doesn't push fluid, so that tells me it's probably toast. Not to mention the paint on the booster is all cracked and peeling as if it's been exposed to a brake fluid leak.

I'm going to go ahead and yank the master cylinder. I suspect I might find a bit of fluid in the booster in the process.

Thanks to all, I'll update with the results later.

 

Gotta ask. Are you closing the bleeder once the pedal reaches bottom, pumping it up, then opening for the pedal to go back down. If you leave the bleeder open when the pedal goes back up your just sucking air into the system.

 

I was using a home made bleeder kit.

But I think we have our answer as to whether it's bad or not. I was pleasantly surprised how easy it was to remove. Dramatically easier than trying to remove a hydroboost assembly I'm used to.

DiNEl5D.jpg
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Yup, its definitely needing a rebuild or replacement.

 

Update: Definitely was the master cylinder. Replaced with a remanufactured unit. Gave the brakes a pump, actually got feel...


...and promptly blew out the right rear brake line and left rear wheel cylinder. At least we have brake pressure and flow to the rear now.