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WJ Master Cylinder


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I am in the process of swapping over a WJ master cylinder and brake booster on the '91 MJ. For some reason I am unable to get it to pump fluid to the line for the front brakes - the rear output on the master cylinder. This is the second junk yard master cylinder that has done this. I exchanged the first one - from a '99 WJ -for the current one - from a '00 WJ - thinking maybe that was why it was a crumpled hunk of metal. But, both have had the same issue. When the pedal is pumped it blows out air and occasionally spits out a little fluid even though the reservoir is full.

 

Any ideas why it isn't pumping any fluid?

 

Thanks,

Willy

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If it's just spitting fluid out the front brake line port it has to be internal to the master cylinder, but very odd two in a row have the same symptom. Pumping okay on the rear brake line port? Combo valve clogged? :hmm:

 

Maybe it would be a good idea to pull the piston and look for the obvious, and throw a rebuild kit on it?

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If it's just spitting fluid out the front brake line port it has to be internal to the master cylinder, but very odd two in a row have the same symptom. Pumping okay on the rear brake line port? Combo valve clogged? :hmm:

 

Maybe it would be a good idea to pull the piston and look for the obvious, and throw a rebuild kit on it?

 

I thought two in a row was pretty strange too.

 

The port for the rear line seems to be pumping fluid. The combination valve has been replaced. The lack of fluid is before the valve, directly from the side port on the master cylinder.

 

A rebuild kit is next on my list. Any tips on rebuilding these? It is the type with a plastic reservoir. I've never torn into one.

 

Thanks,

Willy

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It's pretty easy. I rebuilt the used 96 XJ master before I installed it a few years ago. The only "specialized" tool I needed was a pair of snap ring pliers for this one, not sure about the WJ master. The main thing is to clean it real well after disassembly with brake fluid to get all the crud and possible rubber bits out of the piston passages, blow it out w. low pressure air, and lube well again with brake fluid all the rubber parts before assembly. And of course, bench bleed before installing. This article will help:

 

http://autorepair.about.com/od/brakerelateddiyjobs/l/aa091804e.htm

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  • 1 month later...

A while back I finally got this thing working pretty well. Deb and I have been driving it around some short trips for the past several weeks. A couple weekends ago I trust it enough to take it on a nice trip exploring some old mining towns through the mountains. I noticed one of the brake lines leaking at proportioning valve. Last week I tighten the line, bleed the brakes, and everything is working pretty well again.

 

Thursday rolls around and I decide to take it to our club meeting - which means dealing with stop and go traffic. A few miles down the road I start to smell burning brakes. Not necessarily unusual considering we are surrounded by semis and a Toyota with an egg shaped tire - of course it can't be coming from us. A little further along and the smell hasn't gone away. Time to pull over and check things out. I walk around to the front passenger side to find a nice cloud of smoke coming from the brakes. I was able to nurse it back home and grab my other truck to go to the meeting.

 

I pulled both front tires and the brakes are definitely dragging. I have replaced the master cylinder, pads, and calipers. Why are the calipers not releasing? My best guess is I have heard of the inside of brake lines corroding and acting like a one way valve. I guess that is possible, but the brake lines are in good shape without any soft spots. Anybody else have any ideas?

 

Thanks,

Willy

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Flush or replace the lines?

 

The entire system has been flushed...multiple times. Besides the hard lines, the rubber lines are the only thing I haven't replaced yet. May as well. It will be nice when I can go more than a few weeks without working on the brakes.

 

Willy

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