So the whole not making broken stuff posts was short lived, or rather I'm finally getting around to my XJ's brake issues that have been going on for awhile...

So...ever since I got it, if it sits for awhile (particularly when it rains a lot) and I start driving it, for the first 100 or so feet the rear brakes lock up HARD. I mean a screaching, hard lockup, and then they free up and are totally fine for the rest of the day/week/etc once I drive ~100 feet, leave a parking lot, etc...

Front calipers and pads are brand new. Front hoses were done just before I bought the Jeep and they look brand new. The lines are all (most likely) fine, and I even replaced a rear section not too long ago. I suppose it's possible there's a line that's internally rusted or something but I kinda doubt it.

Took it to a shop today to check out the drums, and he said there's nothing wrong with the rear drums or shoes, the one rear cylinder is slightly leaking but not to cause what is happening. They had taken it out on a road test, and did a few hard stops and saw that only the front left was locking up completely. He also said he didn't feel anything weird in the pedal at all, and I haven't either the whole time I've had it.

They're saying the proportioning valve needs to be replaced. It actually makes sense to me, as the front left (driver's side) would lock up as it is the closest run to the valve, and it kinda makes sense for the rears locking up I guess, since even if the shoes and drums were 100% shot I don't think these symptoms would be happening.

Thoughts? I'm about to go pick it up and I'll get a quote on how much it would be for parts and labor, as he knows I work on the Jeep myself, and will decide from there. Thing is it's freezing/snowing now, and I also don't really like the idea of doing brake work unless I have to usually.

 

Mines been doing same thing. All brake parts have been replaced thru the years not to cure this issue because of either upgrades or failure . Never got it to stop doing it I just live with it now . Chalked it up as character of the breed.

 

I really hope that's not the case, as it definitely does lock up weirdly in general, even with the new brakes up front and all that. I know there's something fishy going on even outside of the total lockup that happens now and then when it sat for awhile. A coworker mentioned he just had his proportioning valve replaced cuz it started locking up his rears BAD, and it fixed the issue - so it does happen....

I'll just be pissed if I pay for it and as you say, it still happens.

I need the brakes to be as good as they can possibly be, even though I know even from the factory they were pretty much garbage. My wife will be driving it alone to work from now on, about 10 miles, nothing over 40mph so not too bad, but still...

It's not a job I'd really be comfortable doing, particularly outside while it's snowing.

He's gonna be able to give me a quote tomorrow. If it's too outrageous I'll just find one on ebay for like $30, or even get a new one for like $80-100 and take it somewhere else.

 

Its easy to change just need line wrenches and brake fluid.I would replace the rear cylinder though any system leak is no good.

 

Ya my friend is saying the same thing, that it's easy to change.

I'd really rather not wait on it, hopefully this weekend it's over 30 outside and not snowing =/

I'll let you know if it fixes the issue.

I'll try to get to the wheel cylinder as well, might as well do it at the same time since I'll need to bleed.

Idk...prolly be leaving this for the spring though, the brakes work so I'll most likely be pushing this off until spring.

 

Always do brake repairs in pairs. If one wheel cyl leaking other will soon.

 

True enough. They're only like $5 a piece anyway.

This is all going to wait until Spring, though. I'd love to get it done, but it just doesn't make sense to mess with it yet.

 

If wheel cylinder craps completely out your gonna be in for rear shoes also .

 

I will also check the front caliper that is locking up, I have seen in the past pistons that accumulate garbage on their sides, and tend to resist themselves to move, had happened to me in both directions, not braking on that tire strong enought, or trying to lock up.
Just my two cents

Hope this gets solved soon, I hate brake problems!

 

Proportioning valve gives a "portion" of the front brakes oomph to the rears to prevent locking.

Will not affect side to side in the fronts.

Last time you bled the brakes well? Didn't replace the rear brake hose?

Wanna see the "guts" of a prop valve?

 

Ya see that's what I was thinking, how simple they are. Huh...

I am actually unsure when it was bled good last, since the last line I had replaced (a small run at the back, one of the metal lines) was at a shop when I was getting it aligned/inspected, but who knows how well they bled it. I would think they would have, and well. Either way it was doing this the entire time I've had the Jeep.

Also like I said, the front hoses (non-metal, to the calipers) were done right before I got the Jeep, which I could tell were like new. The rotors are remanned raybestos with new napa pads I threw on (again, it did this before and after the calipers anyway)

If I do have a bad enough leak though, say at the cylinders, I could I guess have to bleed anyway - but there hasn't been any fluid loss at the reservoir that I could tell, and no visible leaks anywhere ever.

 

Take the prop valve apart and have a gander. Then bleed the whole system.

Easy for me to say. I live in Arizona....

 

If one front is consistently skidding before the other, you might check for grooves in the steering knuckle where the metal edge of the pad presses during breaking. Guys have needed to "weld in" where the metal was missing and re-grind/file, that rail back straight.

Waz wondering if the rears grab at first cuz of rust? There should be rubber plugs in the adjustment slot.

 

I replaced the driver side steering knuckle with one out of a wrangler (same exact one though) simply because that was one of the only parts with substantial rust on the whole jeep, and I wanted to do the ball joints and calipers and u joints anyway. Even still - this has been happening since I got the Jeep, with the original knuckle and original calipers.

I was always suspecting rust for the rears honestly. I still am skeptical, and will probably wind up swapping parts out soon enough.

 

Mine locks up one rear everytime I leave work. It's fine after I get out of the parking lot. Left rear every time.

I have not touched any of the brakes on this *just got it a few weeks ago* but going over all the brakes is on my list of to-do's.

I suspect on mine the rears are massively out of adjustment and perhaps some wheel cylinder leaking or an axle seal leaking.....

I will post and update if I can get mine resolved.