Brake question?

You may have s brake fluid LEAK. check the fluid level. You may even have holes in your brake line or brake hoses....Many people don't know this but brake fluid is an ESTER compound. This means it attracts WATER...moisture from the sir. It then SPOILS and turns brown. Becomes toxic and turns into liquid sandpaper.  It will fit brake hoses and rust the lines inside out. You need to power flush and change the FLUID every 2-3 years BEFORE it turns brown and gets NASTY. CHECK FOR LEAKS.  NOW we have synthetic brake fluid that lasts longer. 

Have you tried asking on Cherokee Forum? Awesome forum.

porportioning valve or still air trapped Try to gravity bleed it Starting farthest away from master cylinder open bleeder and let gravity do its work watching the master not goes dry.@ 5 mins close bleeder and do the same to the rest working closer to the master

step axels for wheel bearings are bend or your bleeding method are wrong

Bleed the *master cylinder* then all 4 cylinders again.

If the brake pedal gets hard when you pump the brake pedal a dozen times without the motor running the rear brake shoes are out of adjustment. Since brake shoes don't get "arced' to fit the new brake drums anymore they will need readjusting after putting a couple of hundred miles on the vehicle. I'd clamp off the rubber brake line at each front caliper and test the way the pedal feels to see if it gets better. many ties the front rubber hoses running to the calipers will swell when the pressure is applied and that will cause mushy brake pedal. Clamp off the rear brakes at the rubber hose to the junction by the rear differential to test if the rear brakes are the problem.

I had a 2000 Cherokee. The brakes were terrible then , so I can only imagine how bad they were on  older models.

Not familiar with your car, but i'd look at the flexible brake hoses, as already mentioned, and a possible leaking past the seal master cylinder. If you press down hard on the pedal does it creep to the floor? If so i'd replace the master cylinder. Does it have ABS? I had this same problem on my 1996 Land Rover Discovery after we had to remove the ABS block to replace the rust in, well, a lot of it :). Bled it four or five times. In the end had to connect via the OBD and make the ECU 'bleed itself' by opening each circuit through the ABS block. Just had to ensure fluid was going into the reservoir and open each bleed nipple in sequence. Got a good firm pedal after that.We'd replaced all four discs and pads and flexible pipes with braided hoses so we were stumped until we tried this.

Brake booster? That is the last thing I can think of that you didn't replace. If you can pump the brake when the car is off and get a stiff pedal, but the brake pedal is squishy during normal driving, then it is more than likely a bad brake booster.

If it bleeds up nice and hard before you start the motor then goes spongy when the motor starts its usually the vacuum booster that causes that.