Rear brakes locking up

[xjdavid1]

I have put new shoes and wheel cylinders on the xj about 500 km ago. The rear is locking up well before the front which is very unusual for an xj. The wheel cylinders were marked 13/16 I have not actually measured them yet. The roughness on the new shoes have worn smooth although they were wareing in the middle for a while because the drum is slightly bigger because is has 80,000 m on them. The leading shoe is shorter than the trailing shoe and is on the front position. The leading shoe is usually short at the top only, these pair are about 1" shorter top and bottom which I have never seen before. Dont know if this is causing the problem. It is quiet odd that the rear should lock as it has a pressure limiting valve. So the problem must be either the shoes or the wheel cyclinders.

 

[Matthew Currie]

This is a pretty common problem. Usually it's the left rear wheel that locks up. Theories abound about why this happens. moisture, pad material,drums,rust,springs.....you name it. I've found that the main culprit on mine is adjustment. Make sure the adjusters are working, and then manually adjust the brakes anyway. I also got the double-short shoes on my last set. They locked up before, and they locked up after. No real difference. The only thing that seems to work for me is manual adjustment.

 

[xjdavid1]

I just adjusted the brakes back 15 clicks and it has not stoped the problem although I think it helped. This has never happened before this set of shoes infact I have never locked the rear brakes before ever and I always got the feeling the rear brakes never did much. The shoe material must be very different. I wonder if the double short shoe is a mistake. These shoes are non genuine and I think they are from Canada. On the subject of brakes I just replaced the front discs with non genuine chinese discs. They were a bit thicker in the part that the wheel studs go through, seem to work alright though.

 

[1986xj]

You didn't mention if the drums were machined before you put them on or not. I never put new shoes on with out having the drums turned, could be that the roughness of the unturned drums is causing lots more friction.
I did have a buddy who had gotten those cheap front rotors and installed them without doing a good job of cleaning that goo that they coat them with to prevent rust off of them and he had almost no front brakes. I ended up redoing them for him and putting another set of pads on since the others had that goo soaked into them. (I also scuff up new rotors with coarse sand paper to help them break in quicker)
Just some thoughts,
Mike B.

 

[xjdavid1]

I didnt machine the drums as they looked very good. But maybe I will have them done now that I am having this much trouble.

 

[Matthew Currie]

I'm a little confused when you say you adjusted the brakes "back 15 clicks." If you actually mean that you backed them off, that's the opposite of what has worked for me. I've found that they need to be just about dragging before the lockup goes away.

 

[8Mud]

I´d have a close look the fronts (might need bleeding), if the rears grab and lock first. Having said that, I had a spring break and it would sometimes cause one rear to lock up early, on another occasion after installing new shoes, my parking brake was a little tight (like one click), also caused the rears to lock first, on wet streets.
Most anytime I have rear brake problems (like noise) I sand the drums and shoes with a 100 grit sealed sand paper, against the direction of rotation (side to side in a cross pattern). Some shoe (and pad) material seems to suck up some moisture and cause problems, until they are heated up.
I always run the adjusters out all the way, grease the threads and the swivel end.
Check the pads for brake fluid contamination, gently pull off a corner of the wheel cylinder dust boot and see if they are seeping. Brake fluid is mostly glycol (suger). Could be causing the pads to stick, it will eventually cook and form a crust.