Hey guys!! as some of you already know I started this story out in the "what did you do to your cherokee today" thread. I figured I'd better start my own thread as it had gotten a little big to be piggy backed into that one. So here goes...Enjoy!

This may not even be the right section to put it in as it is a technical issue but, I am from the PNW and I like to share all of my issues with the guys who read the PNW section.

 

Last night I did a lot of reading and research about a system I've always thought was quite simple. However, the Brakes on my XJ have got me stumped. After developing a spongey pedal I went with the typical "look over everything for leaks" troubleshooting. When I didn't find anything leaking anywhere I logically assumed, since it did have a little pedal at the very bottom of the stroke that the Vacuum Booster was bad. I swapped that out and had no change so I figured the piston cup in the MC was letting the fluid by hence the spongey pedal and no leaking. I was just days away from a weekend campout and wheeling run 200 miles away in Elbe so i threw the new MC at it. Also in the process I found my rear brakes to be totally inop. and the drums were packed tight with mud. I clean it all out and installed new wheel cylinders and brake shoes to both sides. Here is where I started getting P.O.'d. After all of that I had the same spongey pedal with the Brake dash light coming on. The brakes would always stop the Jeep but at the very bottom of the pedal stroke and with fast pumping would pump up. The next brake application it would go right back to the floor with the brake dash light on again. I did a little research online and found procedures for upping the pressure to rear brakes after an axle upgrade. So, i removed the little rubber cup from the piston in the Proportioning Valve and then bled the PV and then bled the brakes. This at first appeared to fix the problem. I had a nice hard pedal while sitting in the driveway. As soon as I took the Jeep out of the driveway for a test drive at the first stop. The pedal went spongey, brake dash light came on and the jeep finally stopped with the pedal on the floor, again. This brake discrepancy has really got this backyard mechanic stumped. If any of you guys have heard of anything that you know that will fix this problem then please let me know. My next step in troubleshooting is going to be to remove the brakeline going to the rear brakes at the PV and at the rear flex hose and blow it out with compressed air. Then open the bleed screws to left then right rear brakes and blow them out individually with compressed air. all i can think of is that I've got some crud or rust in a brakeline somewhere in the system that is blocking proper operatrion and keeping air in the line somewhere.

 

Update to the brake issue I have been dealing with in my 91 XJ. last night I removed the dirty brake fluid from the small front (rear circuit) resevoir in the MC. I took the rear circuit apart where the flex line connects to the hard line at the framerail. I blew high pressure air threw the hardline going to the rear from the MC. I did it from front to rear. Then I did it rear to front. Then I removed the bleeder screw from the right rear wheel cylinder. I blew from the upper end of the rear flex hose through to the right rear wheel cylinder with high pressure air both ways. I reinstalled the right rear bleeder and removed the left rear bleeder and did the high pressure air thing again. I saw some of the nastiest, rusty, sludgey crap come blowing out of those lines, I'd ever seen. In the process, I noticed the junction block where the rear flex hose connects to the axle and the lines to the 2 rear wheels, was loose. I tightened that securely. I also put all of the brakelines back together. I bled the brakes with brand new fresh brake fluid. The Brakes do feel a little more solid and the Brake dash light did go out and not come back on but, the pedal is still lower than I'm used to in this Jeep. I believe it was probably seeping just a little bit out of that rear brake junction but, I also believe the line was clogged with rusty sludge and had some air in there too. I removed the rear wheels and drums to see what kinda mess I had to deal with in there after Rimrock. My guess was right. They were both packed with that nasty sticky mud. I sprayed out both sides with high pressure water and then high pressure air. Then I hit both sides with brake parts cleaner and air again. The wheel cylinders were not leaking around the pistons. This was a good thing as I had just installed them new before the Elbe trip back in May. The bad news is I had also just installed new rear brake shoes at that same time. They were the cheapy Value Craft crap from Autozone. So I got what I'd paid for. The rear brake shoes were completely gone...as in into the rivets on both sides. Pretty crappy considering a couple thousand highway miles and 2 wheeling trips are about all those brakes had on them. So, I figure I will get a little more of my pedal height back once I swap in the new rear brake shoes and adjust them correctly. I've already been on the phone to the local Parts Plus here in Oak Harbor so, I know I'm getting better brake shoes this time. I will give you all another update after the new shoes are installed to let you all know if my brakes are back to normal.

I would suggest to any of you guys who know you have all good brake componants but still have that spongey feeling pedal in your Jeep Cherokee, that you remove the lines at the MC or combo valve, whichever you prefer, and remove all four of your caliper and wheel cylinder bleeder screws and blow all of the lines out really good with shop air. Then, connect all of your lines securely and reinstall all bleeders and fill and bleed your system with fresh brake fluid. I guarantee you, like me, will see 20+ years worth of rust and sludge come spraying out of those lines when that shop air hits them.

 

I installed the new rear brake shoes on Friday evening. That, of course, was in conjunction with cleaning all of the springs and things with the wire wheel and putting a little corrosion prevention on them. I also hit the entire brake backing plates with the wire wheel. That Rimrock mud is some awful stuff and it sticks to everything like Super glue. I am VERY pleased with how the brakes are working now. I can actually stomp the brakes and they will almost put you through the windshield, again. I'm sure it will be short lived as the componants in this braking system just don't seem to last. The main thing I learned in this whole process is the value in breaking the system apart into small sections and thoroughly blowing them out with shop air. I believe without a doubt that I had a rusty sludge blockage in my rear brake circuit that had an air pocket trapped and that was causing the spongey pedal that no amount of bleeding would fix. The loose brake line connection where the rear flex line meets the axle was introducing that extra bit of air that was causing enough to give the difference in pressure to cause the brake dash light to come on. So, I think my next backyard upgrade will be to snag the MC and rear discs off of a V-8 Grand Cherokee ZJ CR44.