Alright, everyone of this forum is probably mine and my girlfriend's dad last sliver of hope. We started the following project going on five days ago now:

Bought a 1994 Cherokee Sport. 4WD, No ABS. At the the time of purchase, the brake system was pretty solid. (We could stop, anyway, pretty well) Over the last couple of months, the pedal began to hit the floor. Could still stop, but poorly. Over the last weeks, the brake system has damn near failed. Had a couple close calls, bumper to bumper traffic is a heart attack and a half. A long overdue day on the brakes finally began. Girlfriend's dad (Eric) and I first started with the front pads. Jacked up the Jeep, removed the tires and found out the calipers were almost to a full seize. Pads surprisingly were in decent shape. Went to Autozone and got a replacement of both front calipers. Bled, tested failed. No pressure on or off. Figured that wouldn't fix it, but did need done. Alright, lets look at that style master cylinder. Full of rust and debris. Went to Autozone and got a replacement of the master cylinder. Bench bled, installed, bled, tested, failed. Did some research, called around and things began to point to the booster. Went to Autozone and got a replacement for booster. Installed, bled, tested failed. Still no pressure within the system. Research, called around.Things pointed to a bad master cylinder. Went to Autozone, got a replacement for the replacement of the master cylinder. Spent an hour bench bleeding,installed, adjusted the booster rod and installed. Bled, tested, pass! We have some rock hard pressure.Except, when we go to start the engine, all pressure is lost. Pedal to the floor. Bled, bled, bled, bled, and bled and still no pressure. As soon as the engine goes off, pressure is rock hard.

So, what have we missed?

Replaced:
Master Cylinder
Booster
Calipers
Bled the system in its entirety

The only thing we haven't replaced is the proportion valve and the rear drums. We've followed every single line and found nothing of an issue. I hope I've supplied enough information. We're on our last leg here.If anyone could supply us any information,it would be gladly appreciated. We look forward to your input!

 

Did u check for leaks? Esp in the rear wheel cylinders.

 

Do the rears. Adjust properly.

Change out the soft lines too, all three of them.


Bleed the ENTIRE system, correctly. Don't just bleed, flush.

 

I would recommend getting one of those cheap vacuum bleeding system like the mitey max and start with the wheel that is farthest from the master cylinder, ie. passenger rear. Then do the next furthest, driver rear - passenger front - driver front.

Clean and dry all brake components. Turn engine on and apply brakes and inspect the system for any leaks. Start from there.

Sometimes its the way the brakes are bled. If the master becomes empty while bleeding, it will let air into the system making braking soft. With a vacuum system there's no pumping the brake pedal, the clear tube will
let you see if air is in the system and the container will let you know how much fluid you're taking out (and how low the fluid is).

 

Pushrod not adjusted correctly.

 

Thanks for the replies, everyone! I took you guys and some more research into account. Replaced the rear drums and rebled the system. RR, LR, RF, LF. Still same deal. Rock hard pressure when off and barely any brakes when on. As for the rod in the booster, we've adjusted it what one of the Autozone guys told us to. Maybe bring it out even more? Again, checked all the lines and everything appears fine. Really at a complete loss here. Ready to sell and another Cherokee.

 

The booster push rod should be adjusted out far enough to where you have good pedal feel but it's not engaging the master cylinder when you're not on the pedal. If it's out too far it will drag the brakes even when you aren't pushing on the pedal. In too far and the pedal will be low and you'll have crappy braking feel.

There's a possibility that the booster you bought was bad out of the box, possibly a bad diaphragm inside. The booster should make it easier to apply pressure, but shouldn't reduce braking power.

 

check to see if the calipers were installed on the correct sides.
bleeder should be above the brake line.

rear wheel cylinders too, bleeders above the brake lines.

 

This is probably the answer. We have the bleeders on the bottom. I'll go out here in a bit and fix it, report back in a few.

 

Excellent post!!

 

Also check the rotors and drums. If there is a significant ridge on the rotors, have them turned or replaced.

 

OP.did the bleeders above the brake lines fix the issue?