Can't bleed my brakes

When trying to bleed the brakes in my 89 XJ after installing a 2000 8.25" axle I heard a noise (maybe a clunk or something) when bleeding and the fluid stopped coming out of the brake line. I couldn't get more than a trickle so I let it gravity bleed for about an hour. That didn't work, the rear still has air and the fluid still just drips from the rear lines. The front has normal pressure when being bled.

Is there a proportioning valve that could have collapsed? Or maybe the line failed internally somewhere? I guess I need to check the entire rear brake line for a wet spot in case it sprang a leak, but it was getting dark. Since there is so much air and undoubtedly tons of air, would holding the brakes give enough fluid leakage to detect a leak?

Inside the front compartment in the master cylinder there was a lot of crap (possibly mud) that I cleaned out after not getting any rear brake pressure. Could that contribute to some internal failure?

Was it mud or just old fluid? If there was actual mud inside. I would consider a new master and flushing all lines they they are clean.

When trying to get a stubborn air bubble out of the system, try pumping the brakes down until the bubble is compressed, then crack the bleeder.

souske said:

Was it mud or just old fluid? If there was actual mud inside. I would consider a new master and flushing all lines they they are clean.

When trying to get a stubborn air bubble out of the system, try pumping the brakes down until the bubble is compressed, then crack the bleeder.

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I don't know. It looked like mud but maybe that's what old crusty fluid looks like? I had to scrape it off the walls and it was blackish/brownish in color.

And I always have my assistant pump the pedal 3 times times before I crack a bleeder.

If you can get ahold of a vaccum bleeder, I would suck out as much of the cruddy fluid as possible, rather than pushing it all through the system. A little piece of poo may have lodged the check valve open.

Hate to be a wet blanket, but it sounds like you toasted the MC from the contamination.

Brake fluid is hygroscopic and draws moisture from the atmosphere--the more contamination the less effective the brakes become.

Crack the line connection at the MC for the rear brakes--no pressure there, R&R the MC.

Ok, I need to buy a set of line wrenches so I can safely loosen the master cylinder's rear brake line to see if there's pressure there.

Souske, is the check valve in the proportioning valve or somewhere else?

Follow the lines from the master cylinder to the prop valve mounted kinda below it.

I never use the brake pedal to bleed anymore, got a pressure bleeder, and just add a can of fluid to the tank, screw the bleeders cap on the master, pump it to about 15lbs and go around and bleed the system. No more pushing the plunger past the corrosion and fubaring it up.