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Brakes not releasing after 2000 WJ Upgrade

P

PapasXJ

NAXJA Forum User
Location
Northern Nevada
I installed the booster and master cylinder from a 2000 WJ into my 1992 XJ. During the test drive, I braked easy twice. After the third stop the brakes wouldn't release. I loosened up the two bolts holding the master cylinder and pulled it back to release the built up vacuum. The brakes release immediately. Got it home but letting the pads cool before I try it again.

Any ideas what caused this.
 
I've heard of people having to add a proportioning valve in some cases where they modify the brakes, but I don't know for sure if that could be affecting you. Was it the front brakes that locked, rear, or all 4?
 
what modifications did you do to the pedal rod on the booster to get it to fit onto the pedal assembly? it is not a direct bolt in most have to either change out the rod or modify the pedal to get it to work right.
 
Darky said:
I've heard of people having to add a proportioning valve in some cases where they modify the brakes, but I don't know for sure if that could be affecting you. Was it the front brakes that locked, rear, or all 4?
Click to expand...

Since I was on the side of the road I only lifted the R pass front. So I only verified that the front was locked. As for the adjustable P-valve, I added one in line with the rear. I also removed the rubber disc from the factory valve until I can remove the entire OEM valve.

GrimmJeeper said:
what modifications did you do to the pedal rod on the booster to get it to fit onto the pedal assembly? it is not a direct bolt in most have to either change out the rod or modify the pedal to get it to work right.
Click to expand...

I didn't have to drill out the hole. I checked them both with calipers and where within .002-.005" so it slid right on my existing pedal. The drop in hole alignment seemed slight and the peddle always return to the top of travel.

I have added a 1/4" spacer between the booster and firewall and will test drive tonight after work.
 
Last edited:
98stocker said:
Stuck check valve in the booster vacuum line?
Click to expand...

That was going to be my next check. But, placing a 1/4" spacer between the firewall and booster appears to have fixed the problem. It resulted in a bit more free peddle and the top of the stroke and they work fine now. I was also able to adjust the p-valve to get the rear discs to lock up just after the front.
 
montanaman said:
I've heard of other people doing that too.

Are you getting better braking performance now, vs. your stock mc/booster?
Click to expand...

as someone who has done this i will say it is a huge difference, one of the best jy upgrades i did on my 90.

i also used a spacer on mine, but only because the guide i used told me to do so. guess i know why now.
 
The guide I used read as to suggest the spacer was optional. Being in the high 90's the day I went to Pick N Pull I really didn't want to hunt one down so I opted to go without. Well, the spacer is not optional. I made mine out of .210" plexiglass.

As for performance: They are great. Driving into work today I came on a late yellow light. Applying the brakes as I normally do I stopped nearly two car lengths short of the limit line.
 
98stocker said:
Stuck check valve in the booster vacuum line?
Click to expand...

How? Its a check valve. It only allows vacuum. If it was stuck in some way you would lose power brakes.


Did the MC and booster come form the same vehicle? Sounds like the booster rod is too long.
 
Glad to read the rig is good Steve!
 
Ok ... some more questions about this. Did you use the WJ MC/booster on stock XJ calipers and rear wheel cylinders? And still got better stopping?

About the spacer, what if you shortened the push rod, instead of using a spacer? Wouldn't that do the same thing?
 
montanaman said:
Ok ... some more questions about this. Did you use the WJ MC/booster on stock XJ calipers and rear wheel cylinders? And still got better stopping?

About the spacer, what if you shortened the push rod, instead of using a spacer? Wouldn't that do the same thing?
Click to expand...

Actually no. I have a ford 8.8 rear and ford D44 front.
The push rod on mine wasn't adjustable.
 
PapasXJ said:
I was also able to adjust the p-valve to get the rear discs to lock up just after the front.
Click to expand...

I'm thinking of putting ZJ discs on my D-35, and keeping the front D-30 with stock brakes. ... I just rebuilt my entire brake system 2 years ago.

- Would the WJ MC/Booster be a good match for that system?

- What P-valve did you use? How did you adjust it? Anything special required to do that?

- Anybody know a good source for Jeep WJ MC rebuild kits? I want to get a junkyard MC/booster, and rebuild it myself and do it right.

Thanks.
 
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