Rogue4x4

Well the prop valve regulates the amount of pressure applied to the rears. It might be stuck or have a blockage of some sort...take it out and clean it and try again but I would also have another on hand to replace if it is bad. The soft pedal may be the mc starting to go, it might be starting to bypass. One thing at a time though...lol...eliminate the rear brake problem first then see how the pedal is after you check the valve and bleed...Also have you done a complete flush of the system, and how did you bleed them? Might wanna try a reverse flush and then gravity bleed just to make sure all the air is out...

DFlintstone

I've read the propositioning valve can be "reset" by really pressing the brake. They mentioned passing some high psi. This would, (of course) be with everything else holding.

Is what you are describing what would happen it there were a problem with the fronts? You have bled them, and the bleeders are top, on the calipers? When you say "locks up" it doesn't stay locked up?

Backing off two turns is too much, (in my opinion). I'll just leave slight drag with new shoes.

Yea, the "short shoe" goes forward.

freegdr

Seeing how both are doing same thing could damage of occurred to rubber brake line not letting fluid return as fast as master can push it thru Causing brakes to stay applied slightly ?

sicma99ot

so i replaced my master cylinder and prop valve this evening. i used the PV and MC from my junker 96 xj.


coming home from work the rear brakes would lock up when coming to a stop. by lock up i mean the drums would lock when coming to a stop, but would release when letting off the peddle.


i inspected the rear drums first. i took notice that the wheels spin freely without dragging. i also took notice that the adjusters were the same as i had left them when i adjusted them a couple weeks prior. i did not touch the adjusters at any point. i did however put some grease on the backing plates at the contact points and springs to keep them from sqeaking when moving.


next i completly drained the system of the old brake fluid. and installed the new (used) MC and PV. i refilled the system and gravity bled it. i also had the wife help do a 2 person bleed (a method im more experianced with). i did not adjust the drums at all and left them the same as when i started, with no drag.


when i got into the jeep i pump the peddle until firm. 3 or 4 pumps gradually getting firmer with each pump. held the peddle, no sinking. started the engine still holding and peddle falls. i notice its still soft but doesnt go to the floor. i go back and fourth in the driveway.


i go around the neighborhood driving normal stopping pretty hard at stop signs. dosent lock up coming to a stop, in D or N. next i get onto an empty 55mph 2 lane road. i get up to 60 and slam on the brakes. gets a little squirly but i can keep it in my lane without much effort. and come to a stop rather quickly. peddles still pretty soft. though i came to a tire screeching and rubber smelling halt with a good amount of effort, neither the rears nor fronts lock up.


i do several passes, coming to a stop in both D and N at 60mph. each time i get the same result. it seems the brakes are about 50/50 give or take front or rear.


now buckle up for this one and be brave.
i get on the state road (4 lane, 2 way, 45mph, redlights) and get to 55mph coming up to a redlight and hit the brakes when the dotted white line turns sold (still, no cars around me). im able to stop without locking up or screaching any of the tires well before the light. still 50/50 braking, maybe nose diving a little bit. the peddle still feels soft but i can stop quickly with out locking any tires. i drive normally the rest of the way home.


im thinking brake booster is the cause for the soft peddle. i could probably adjust the rears to alittle drag to firm it up, but might get the rears locking up again when braking hard. so ill leave the drums alone for now and just deal with a soft peddle for a little while. i will probably use the booster from the junker 96.

sicma99ot

i dont suspect the front calipers might be bad. i never touched the calipers when puttin in my lift, just the brake lines. braided stainless extended lines from rubicon express. they were properly bled with bleeder valves at the top of the caliper doing a 2 person bleed.


i may not have turned the adjusters 2 full turns (or any full turns for that matter). thats my bad. i have adjusted both ways. with a little drag and with no drag, to where they free spin. both ways ive ended up the rear drums locking up at stops eventually. by locking up i mean when i hit the brake the rears stop moving while the fronts continue to roll, coming to a screeching stop. when i release the peddle, the brakes release and all 4 roll. they do not stay locked.

sicma99ot

front and back have braided extended lines. i blew through all the lines from master cylinder to calipers/wheel cylinders, using my mouth (tasty) but none were stopped up and had the same amount of resistance.

DFlintstone

OK. I didn't mean "bad" on the front calipers. They can be installed reversed, with the right on the left, left on right, then the bleeders come out on the bottoms. Poeple do actually do that, I just wanted to be sure. You would get a spongy petal and lack of action on the fronts if that were the case.

sicma99ot

lmao i have actually seen this when i was working at sears auto center (aka hell). i was there for like 3 months.


a buddy of mine put my inlaws front pads on backwards. not backwards like outside pad went on the inside, but the metal clips pointing in . id have called bs if i didnt see it with my own eyes. lol.

lgryder

Do a disc conversion, rear drums suck. Get a set off a zj and the prop valve.

sicma99ot

Id love to. And as ive said before its on my list in the not to distant future. But have other things I need first. For now id just like to get my drums functioning reliably like they have been the last five years ive owned my xj. Never had any problems before this.

sicma99ot

$h!t. I just realized I didnt bleed the MC. I just swapped in the new (used) one and bled the system as usual. Is this going to cause a problem? If so can I drive it tomorrow without my jeep blowing up? And could this be causing my soft peddle?

DFlintstone

Roughly what I waz getting at. Make sure there is no air in the fronts. If they are bleeding without bubbles, that is not your issue, I'd suppose.

freegdr

Very possible fronts not working properly causing rears to lock because there doing more of the work .

sicma99ot

It looks like when I bleed I get all the air bubbles out. Im going to use a clear rubber tube to make sure.

how about the MC. Do I need to bench bleed that? How would I do that?

freegdr

Pump the pedal then crack the lines while holding a rag around it or locate a bleeder kit . Then rebleed brakes in sequence again.