Oldred87 Posted June 18, 2012 Share Posted June 18, 2012 So been going through my brake system the pass couple weeks and put all new lines a new master cylinder and booster. Went to check on the propotional valve and seems the pin inside is hanging up not letting me get rear brake. Was just wondering if anybody knew how to fix this or any where i can get a system that would work since everytime i search i never can find one. Maybe another one from a different vehicle will work. thanks Link to comment Share on other sites More sharing options...
Eagle Posted June 18, 2012 Share Posted June 18, 2012 There is no pin inside. Are you asking about the "thingie" up front, next to/beneath the master cylinder? That's the proportioning valve on an XJ, but not on an MJ. On the MJ the proportioning valve is in the rar, and it changes the brake bias depending on how much weight is in the bed. Link to comment Share on other sites More sharing options...
Oldred87 Posted June 19, 2012 Author Share Posted June 19, 2012 Yes thats the piece I'm talking about underneath the master cylinder their is a little valve or pin whatever you would call it that is hanging up on me trying to find a way to get it to move guessing it is something different on the mj so guess he cj would be different. Thanks Link to comment Share on other sites More sharing options...
Eagle Posted June 19, 2012 Share Posted June 19, 2012 Yes thats the piece I'm talking about underneath the master cylinder their is a little valve or pin whatever you would call it that is hanging up on me trying to find a way to get it to move guessing it is something different on the mj so guess he cj would be different. Thanks The slider on the top? That's what turns on the brake system warning light in the event of a loss of brake pressure. It is reset to the center position after bleeding the brakes by stomping on the brake peddle -- HARD! It cannot cause a complete loss of rear brakes. Here's a photo of it, cut in half. The rear brakes are fed through the horizontal port on the left of the photo (the end that faces the front as installed in the truck). Link to comment Share on other sites More sharing options...
Oldred87 Posted June 19, 2012 Author Share Posted June 19, 2012 Yeah thats the piece that is giving me trouble i still have some brake to the rear but when bleeding the rear the pedal never really builds pressure when pressed or it is inconsistent in building pressure. When i plugged the rears and just bleed the fronts it worked great. I know this piece pictured above distributes which way the brake fluid goes being front or rear. Gonna see if this fixes the problem if not gonna check out the wheel cylinder in the rear even though i doubt i is because no fluid is leaking back there like it would if a cylinder was bad. Link to comment Share on other sites More sharing options...
Eagle Posted June 19, 2012 Share Posted June 19, 2012 Yeah thats the piece that is giving me trouble i still have some brake to the rear but when bleeding the rear the pedal never really builds pressure when pressed or it is inconsistent in building pressure. When i plugged the rears and just bleed the fronts it worked great. I know this piece pictured above distributes which way the brake fluid goes being front or rear. Gonna see if this fixes the problem if not gonna check out the wheel cylinder in the rear even though i doubt i is because no fluid is leaking back there like it would if a cylinder was bad. No, that sliding piece does NOT distribute which way the fluid goes. Look at that photo, at the "nose" of the metering block. The front (left) top is the fluid inlet for the rear brake circuit. Notice that it connects directly to the nose outlet, which is the line that goes to the rear. What controls how much brake force actually gets to the rear wheels is the rear height-sensing proportioning valve. And because the MJ has that rear proportioning valve, there is also a second, bypass line from the front to the rear. There is a very specific bleeding procedure that must be followed when doing the MJ brakes in order to get that bypass line bled. Since you didn't even know where your proportioning valve is, I suspect you were not aware that this procedure is necessary. Detailed instructions have been posted here a couple of times in the past. Link to comment Share on other sites More sharing options...
Eagle Posted June 19, 2012 Share Posted June 19, 2012 Here's the official FSM procedure to follow when bleeding the brakes on an MJ that still has the two lines to the rear: After bleeding the brake calipers and cylinders the rear brake by-pass line must also be bled. Open a front caliper bleed fitting and depress the brake pedal to the floor. This will shuttle the by-pass differential valve and allow fluid to flow through the by-pass line. The brake warning light on the instrument panel will illuminate when the ignition key is in the ON position. This signals the shuttling of the valve. Re-Bleed the rear brake cylinders with the front caliper bleed fitting open. After re-bleeding the rear brake cylinders the entire system must be bled again. Bleed the brake calipers and cylinders in the following sequence: 1st -- Right rear 2nd -- Left rear 3rd -- Right front 4th -- Left front Link to comment Share on other sites More sharing options...
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