First post, long story. I'll try to make it readable.

1996 Cherokee Sport. Recently purchased so it's new to me. Was told "rear brakes need to be rebuilt"..... that hasn't turned out to be exactly accurate.

Parts fell out of the rear drums when they were first pulled off. Overhauled both sides and new pads. Drums and wheel cylinders seemed ok so they did not get replaced. Still mushy brakes.

The next course of action was a good bleed. Cracked bleeder screw and couldn't get any fluid from either rear side.
Replaced with used master cylinder and prop valve from pull-a-part. Ruined one of the prop valve inlets putting them in so put in a new prop valve.

At that point, most of the brake line fittings were stripped or partially stripped so took the time/money and replaced all of the brake lines including the hydraulic line that fits onto the rear axle. I own a couple of nice line wrenches now.

Finally started getting fluid to the rear.

The right front caliper wouldn't stop bubbling so replaced it and put in an extended brake hose. Believe it was sucking in air when the pedal came up.

I bled it again and finally started to get pressure. Turned on to test drive and brake pedal hit the floor.

Replaced booster.

Continued attempts to bleed at this point are yielding almost no pressure. There are no leaks. I'm not seeing any air while bleeding.

Two weird things(weird to me) are occurring now:
1. The rubber seal from the cap on the brake fluid reservoir is pressurizing. Pop the cap off and that seal has to be pinched off. It's a brand new cap
2. When I open the bleeder screw it seems like there is back pressure sucking the fluid/air bubbles back into the caliper. I've bled brakes before but I don't recall if this is normal behavior.

I'm suspecting the master cylinder is bad but I'm getting tired of throwing parts at it. The only not new parts involved in the braking system are front left caliper and hose, both rear wheel cylinders and the master cylinder.

I'd really appreciate any thoughts or advice on how to proceed. My gut is saying to replace everything not new. It's obvious this Cherokee has been in a lot of mud/water AND has lots of signs of sitting for an extended period.

 

Vacuum problem for brake booster? Maybe a small leak in a rubber line somewhere that's allowing air to get in and also not allow pressure to build when the pedal is hit...??? These are all guesses. I've never had to dig into my brake system yet since I've only owned an XJ for about 7 months, but a brake system is a brake system for the most part, regardless of the vehicle. They work on the same theory.

 

Finally got this corrected with a new master cylinder. Bench bled prior to install.

I will probably replace the wheel cylinders, front left caliper and hose soon but need a break from brakes.

 

While you are overhauling the brake system this would be a perfect time to do a rear disk upgrade!