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WJ brake booster swap...soft pedal, light engage struggles?

Muddy Beast

Muddy Beast

NAXJA Forum User
Location
WA
Did my WJ booster swap into my '89 with ABS, and also put in a ZJ prop valve. Well finally got it all bled and all the lines installed with my 8.8 with disc, and I find it odd how my pedal will go all the way to the floor with almost no presure, but it still stops just fine. I have to push two inchs or so before the brakes engage but after that it stops no problem. I was wondering if it's normal to not have to apply a HUGE amount of pressure like I did before, and if it's normal for it to no engage for a little bit?

Also, I put my old light switch on, and it doesn't quite engage on its own. So to help (I read another guy did this on here...so I tried it) I put a zip tie between the sensor and the brake rod just a little bit, and now it engages perfectly. My question is, is there any sort of adjustment so I can pull the zip tie out? I read in my service manual there is, but I can't for the life of me figure it out.

~Scott
 
mine is the same way, makes a nice whistling sound too... probably a leak at the pedal side of the booster. it does stop on a dime and give me 6 cents change though.
 
I read somewhere that you have to space the WJ booster about a 1/4" off the firewall when swapped into an XJ. Sounds to me like a freeplay adjustment on the pedal.
 
squidd said:
I read somewhere that you have to space the WJ booster about a 1/4" off the firewall when swapped into an XJ. Sounds to me like a freeplay adjustment on the pedal.
Click to expand...

x2 on spacing it that 1/4" 4x4wire has a write up on it which i plan to do especially after this last weekend where i barely made it to my campin trip as the stupid brakes didnt wanna stop when it really needed to and as for the light switch did you grind the rod flat where it hits the switch if not it wont activate properly but thats all in the write up
 
I just did this swap this last week myself.
The pedal shouldn't go down very far at all and should push easy but brakes should grab HARD. I was really surprised.
Did you bench bleed the master cylinder? If so you might have a bad one.
About the light issue:
How tight is the bushing in the booster rod? It should be slightly sloppy (like 1/8" +/-)
If it's a tight fit like I made mine, take the nylon bushing out, that should be enough.
If still no luck you might need to put a shim where you have the zip-tie, I used a piece of aluminum.
 
I used a spacer...still don't really have a good solution for the brake lights though...pedal wise I'm working on that.

~Scott
 
did you do the master swapp also or just the booster?

sounds like you need to continue to bleed the system.

i did the booster/master swap on my 89 and had to bleed the system a few times to get all the air out. might want to gravity or vacuum bleed the system.

i didnt use the spacer and it sits at the same height as my clutch. getting the brake light switch was my biggest issue but resolved the problem by not using the plastic washer.
 
89xj said:
did you do the master swapp also or just the booster?

sounds like you need to continue to bleed the system.

i did the booster/master swap on my 89 and had to bleed the system a few times to get all the air out. might want to gravity or vacuum bleed the system.

i didnt use the spacer and it sits at the same height as my clutch. getting the brake light switch was my biggest issue but resolved the problem by not using the plastic washer.
Click to expand...

I used both the booster and master cylinder as well as a ZJ prop valve from an ABS converted to work without ABS. I've bled the system a couple times, pedal is slowly getting better. I'm using a pump to bleed, but for whatever reason my front brakes wont have any fluid coming out when I bleed them...

~Scott
 
Muddy Beast said:
I used both the booster and master cylinder as well as a ZJ prop valve from an ABS converted to work without ABS. I've bled the system a couple times, pedal is slowly getting better. I'm using a pump to bleed, but for whatever reason my front brakes wont have any fluid coming out when I bleed them...

~Scott
Click to expand...

crack the output line for the front brakes at the prop valve to see if fluid comes out, if not fluid comes out then something is wrong with the valve or at the master. crack the connection for the inlet side of the prop valve for the front brakes and see if fluid comes out. you need to fine where fluid has stopped flowing for the front brake curcuit. think of the as an electrical problem and you need to trace where flow has stopped.
 
I think the only difference on the prop valves is the fitting that is plugged on a non has a line running to it for the additional line port.
 
Talyn said:
What did you do to make the prop valve work without ABS?
Click to expand...

Like James said above, there's two plugged lines in the ZJ one for ABS, and to make it OK for non-ABS use you just pull them and put in your lines. I know all my brakes work because the rust has all worn off.

~Scott
 
I know tnis old but im diggin it up.

I did this swap the other day. Didn't use the spacer. Apparently im going to have to. When I hooked the rod to the pedal I had to push it in a 1/4 inch or so to get it on. It was a huge pain since the rod isn't easy to push in by hand. apparently by doing that I put pressure on the brakes and they were dragging. I learned today that when brakes get hot they get progressivly tighter. And tighter untill its like you're standing on the brakes.

Am I right in my thinking? The brakes got hot and now the front is locked down hard. Cool off, in the spacer and I should be fine.

I've been sitting here for half an hour and they still are locked hard. What causes them to get grab progressivly harder? The pedal got really stiff also. Both are locked up evenly.
 
Last edited:
when brakes get hot they fade and stop working as well or at all.

something else is wrong.
 
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