A heads up for those looking to swap in a ZJ proportioning valve.

I just finished putting rear discs on my XJ using pre-1991 front calipers and front rotors. I also put a dual diaphragm booster in from a 1996 ZJ and was planning on swapping the ZJ proportioning valve in as well.

However! Upon closer inspection my old 88 XJ prop valve and the 1996 ZJ prop valve I noticed they are virtually identical except for they each use a different spring. So instead of fighting to remove those stuck old brake lines I just swapped the ZJ prop valve spring into my old XJ prop valve.

Works great.

Bender said:

Works great.

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Thanks for the info, its the last thing i had to find out . Got to get the guts of a ZJ valve now.

Good to hear it worked as I thought it would.

Good tip. I'm headed to the junkyard this weekend for that very upgrade. Saves me from pulling a few lines, and a spring fits in the pocket ;-).

Does replacing the spring like this still require bleeding the brakes?
I've got a ZJ prop valve sitting in the back of my jeep and been holding off installing it cause I just don't have the time to deal with hard lines, bleeding, etc.

Well,

maybe a dumbass question, but I installed disc brakes (d35 non-Cklip) last year, and didn´t replace proportioning valve, than I granaded the axle, put on again an axle with drums. Exept of better braking with discs and than worse with drums again, I didn´t notice anything. What is proportioning valve good for??:roll:

Not much on the XJ, and ZJ except in a hard braking appication. Then the difference is on tho amount of fluid sent to the rear.

ok, so not a big mistake I did?

You must bleed the brakes after swapping all the internals over. You might only need to bleed it at the proporting valve only and the rest might be alright. You will know quick enough after you feel the pedal afterwards. I have done it this way when I tried it without the cup in place and then had to put it back when it caused lockups too early on the rear and lost braking due to that.
Day to day driving is un-changed due to both valves being 50/50 under light to moderate braking. It is only under hard braking that the ratio changes and the ZJ one then runs a different ratio to the rear to suit the discs.

Gojeep said:

It is only under hard braking that the ratio changes and the ZJ one then runs a different ratio to the rear to suit the discs.

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how do you figure...is the spring valve preloaded to a different level? guess i dont know how the prop valve works under light vs. heavy braking.

Under heavy braking, the fluid pushes against the cup on the piston and the spring pressure behind it determines how far the piston will move changing the fluid ratio front to rear.

OUTSTANDING.... i was going to ask this exact thing... i had my '96ZJ valve and was thinking it looked dead on the same...even the wiring... but now that someone said i can just swap the innerds....i feel better about doing it.

BTW....did you change the master cylinder or booster? ...

also....anyone have a problem bleeding their system after the install on ZJ discs? i'm having a B!$&% of a time....

....back to the :repair:

The MC is exactly the same, part number and all. Never heard of anyone bothering to swap the booster so I take it it either doesn't fit or is no better.

When I did my swap i was going from a 1988 XJ brake system to a 1996 ZJ so I swapped the booster, master, and changed the spring in the proportioning valve.

In the end I still have too much braking at the rear but that's more than likely caused by the fact I used all front brake hardware back there...i.e. 10" vented rotors and big front calipers. The ZJ proportioning valve is designed for smaller rear calipers

sweat.....thanks guys... I'll be sure to swap mine in soon as i get home... right now my brakes just seem soft...so hopefully that will solve it.

I should add that after swapping the dual diaphragm booster and ZJ master I initially thought my master was dead because while parked in the driveway I could push the pedal to the floor fairly easily. Turns out it was just the extra assist provided by the booster which makes a really light pedal feel. When I get on the road the pedal moves really easy but will lock up my 35's.

I just picked up a 94 ZJ master cyl (looked new) and proportioning valve internal components (4 wheel disc with ABS) to go with the 95 XJ dual booster i have. I run TSM rear discs on my 44.

During inspection i find that not only is the spring shorter in length but the other components are different also.

After pulling the internals from the ZJ's prop valve i found it had a bad o-ring on the plunger...so i went to a 95 XJ in the yard and pulled the props internals from that to find that the o-ring is identical. While i had both apart i was interested in what the difference was. First obvious difference was the spring, but after careful inspection i found the ZJ plunger has a smaller OD where it inserts into the end cap...which makes the end cap different also.

It also apperars that the ZJ's plunger may have a smaller ID also..but not by much.

So now i'm wondering since i dont know exactly how a prop valve works is if all i need to do is swap springs as mentioned in this thread or swap spring,plunger and end cap. Does anyone have input?

I would assume if using all ZJ internals it'll have the same pressures as stock...but whats happening if i mix the XJ internals with ZJ spring? Which option would i get better results?

I figured i may have lost some in my explanation so i took some pics, i'll get them up a bit later. :confused1

Bender said:

I should add that after swapping the dual diaphragm booster and ZJ master I initially thought my master was dead because while parked in the driveway I could push the pedal to the floor fairly easily. Turns out it was just the extra assist provided by the booster which makes a really light pedal feel. When I get on the road the pedal moves really easy but will lock up my 35's.

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Explain easy pedal. I know you are going from old, to 96+ brakes. I have a 00'. I have discs on the Isuzu 44. I completely removed my ABS. I swapped in a ZJ prop valve. My pedal is very stiff. I have tested the booster and know it is working. My XJ is my DD and I don't give the brakes much thought. They work. However, any time I drive my other cars, what a difference! Is there something wrong, or is this just the way it is?

Also, for the person that is having a hard time bleeding the brakes. You mentioned adding discs. Are the bleed valves on the top or the bottom of the calipers. Sorry if that is obvious. I had to learn that one the hard way.

XJ internals on left, ZJ internals on right.

Anyone else put a 99 up GK Booster and master with a 97 porp valve with rear disks?? I did this along with a crown vic rear disk setup on my Comanche d44 and it stops great and i dident have to moove anything to get the booster in because it has good power but is more compact than the never xj ones. dont forget to get that 1/4 in alum spacer from between the firewalle and the booster from a 97X xj then just ream the hole that attaches to the pedal on the new booster a bit. Works good