rear wheels lock up when i hit the brakes ?!?!

[one_bad_MJ]

well my rear wheels lock up when i hit the brakes, what causes that.

 

the other day i was going up 119 and it was wet out and it happened i fish tailed and spun out on the highway lucky no one was around. and when i leave my house in the morn after it sits all night my first stop sign the rear tires lock up and drag.

[DJM/78]

Adjust and clean the rear drums , check the lines and anything else that could be wrong , sometimes its just rusty drums . I went with discs in the rear so I did away with most of those problems .

[Pete M]

does your truck still have the rear proportioning valve?

[dasbulliwagen]

Even with the rear valve unhooked, it shouldnt lock up this easilly. Could be a wheels cyl leak too causing them to grab... you definitely need to take them apart and inspect everything.

[one_bad_MJ]

no leaks. rear pads do need changed but no mechanical issues hat i can see.

 

post a pict of this rear porp valve. someone has a T where the lines goes from the front to the rear and it t's back tot he front maby it was there and they deleted it.

[87Chief]

That could be caused by scored drums... Rub your finger up and down the inside of your drum, make sure no hot spots or big cracks.. Then pull up your rubber boot around your brake cylinder and if fluid comes out, you need a new one, if just a little fluid comes out, that's ok..

[Pete M]

if you have a T in the fittings, then someone removed the prop valve. If nothing else is found to be wrong, I'd look into an aftermarket prop valve for adjusting the rears.

 

 

factory unit:

 

[Eagle]

If this is mostly on damp days, especially just for the first couple of stops in the morning after being parked overnight -- it's because the rear shoe lining material absorbed moisture and swelled up. Same thing happens with my '88 XJ.

 

The solution is to replace with semi-metallic or ceramic shoes.

[HOrnbrod]

if you have a T in the fittings, then someone removed the prop valve. If nothing else is found to be wrong, I'd look into an aftermarket prop valve for adjusting the rears.

 

factory unit:

 

 

Plagiarizer. :waving:

[Pete M]

google gave it to me. :yes:

[HOrnbrod]

:cheers:

[one_bad_MJ]

If this is mostly on damp days, especially just for the first couple of stops in the morning after being parked overnight -- it's because the rear shoe lining material absorbed moisture and swelled up. Same thing happens with my '88 XJ.

 

The solution is to replace with semi-metallic or ceramic shoes.

 

 

my 89xj did it to sometimes also

[LarryH88bt]

Same here. My XJ brakes grab when wet until I roll a ways and brake a few times. On the MJ, the rears squeel like a dump truck, grab a bit the first couple stops then they clear out.

[one_bad_MJ]

Same here. My XJ brakes grab when wet until I roll a ways and brake a few times. On the MJ, the rears squeel like a dump truck, grab a bit the first couple stops then they clear out.

 

i wish there was a fix because one day they locked up when i braked for a red light and i was all over the road every which way but upside down

[ParadiseMJ]

To the OP, there are numerous threads on the "right" way to fix the rear lock up issue. Some insist that swapping out an XJ prop valve, some just keep the MJ prop valve, block one of the rear brake line and plugging it. Even others say to plug the lower front line on the prop valve and install an after market adjustable prop valve.

 

It sounds like you should consider the last option. This doesn't sound like rusty shoes or even fluid on the shoes, it sounds to ME (who doesn't know much about this system) like a fluid delivery problem, like full braking to the rear as if you were loaded down.

 

What position should the height sensing valve be at when the truck is sitting, unloaded so that I can set it at the right spot with the new fittings and threaded rod? Level with ground, slightly up, slightly down??...and how do I get the fluid to flow through it. Slight hijack, I know, sorry guys, but it's relavent. I'm still working on the fix for this. I want to keep the height sensing valve and so I'm trying to do the fix in the picture above.

[shawn]

i followed the thread on here to do the by-pass and kept the mj distribution block under the hood. -its working great and i am pleased. all of the replies about cleaning the drums and checking the wheel cylinders and damp, swollen pads are probably what is going on with your truck, but i would also look at the front distribution block and make it so the line to the rear is coming out the front of the block and the original outlet is plugged. ----- it seemed to work well for me doing it this way.

[HOrnbrod]

What position should the height sensing valve be at when the truck is sitting, unloaded so that I can set it at the right spot with the new fittings and threaded rod? Level with ground, slightly up, slightly down??...and how do I get the fluid to flow through it. Slight hijack, I know, sorry guys, but it's relavent. I'm still working on the fix for this. I want to keep the height sensing valve and so I'm trying to do the fix in the picture above.

 

I found the best adjustment for me was with the arm slightly UP from the axle, maybe 10-20 degrees. :cheers:

[ParadiseMJ]

I found the best adjustment for me was with the arm slightly UP from the axle, maybe 10-20 degrees. :cheers:

 

Thanks. I needed to know whether to make the threaded rod longer or shorter. I'll go out there now and make the cut.

 

...and OP, sorry about the side track. Paradise - out.