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  #1  
Old March 10th, 2008, 20:52
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ZJ Proportioning Valve

Just did a rear 8.8 swap, I'm only somewhat impressed by the improved braking. My next big mod is to add a dual diaphragm booster, but in the meantime..

Does the ZJ prortioning valve let MORE or LESS fluid through than the stock prop. valve?
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  #2  
Old March 11th, 2008, 15:37
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Re: ZJ Proportioning Valve

The ZJ valve opens the front brake circuit faster, restoring your pedal feel and your braking with the discs in the rear.

Your stock valve is designed to push a bunch of fluid into the rear wheel cylinders on the drum brakes, so there is a pause to allow the drums to build pressure before the front calipers are applied.

With the rear discs installed, you're getting a delayed front caliper action that's not needed anymore because you have calipers in the rear that don't require that volume of fluid to actuate. The ZJ valve is internally compensated for that because the ZJ's had rear discs.
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Old March 11th, 2008, 16:35
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Re: ZJ Proportioning Valve

Quote:
Originally Posted by RedHeep
The ZJ valve opens the front brake circuit faster, restoring your pedal feel and your braking with the discs in the rear.

Your stock valve is designed to push a bunch of fluid into the rear wheel cylinders on the drum brakes, so there is a pause to allow the drums to build pressure before the front calipers are applied.

With the rear discs installed, you're getting a delayed front caliper action that's not needed anymore because you have calipers in the rear that don't require that volume of fluid to actuate. The ZJ valve is internally compensated for that because the ZJ's had rear discs.
Thank you for the detailed explination, I appreciate it.

So adding this valve should make the braking a little more immediate, and therefore worth it?

Looks like I'll be going junkyarding before too long.
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Old March 11th, 2008, 16:37
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Re: ZJ Proportioning Valve

I have one I haven't installed yet, but that's the general consensus.

Others have installed it and reported positive results.
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Old March 11th, 2008, 20:36
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Re: ZJ Proportioning Valve

I have the Explorer rears and even though I have a 2000 with the dual diaphragm, was not happy . CleanRc told me to install a WJ booster and proportioning valve, It Rocks.
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Old March 12th, 2008, 09:26
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Re: ZJ Proportioning Valve

I'm doing a rear disc swap on a d44 out of an 87 XJ. Would you recommend the ZJ proportioning valve for this? I've heard it's a good mod, but not always necessary.
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  #7  
Old March 12th, 2008, 11:37
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Re: ZJ Proportioning Valve

I've heard it's a good mod, but not always necessary.
============================================
Some disable the stock value by pulling the O rings out. But (IMO) the would also disable the independence of the two systems. (front and back)
If you pop a line anywhere you lose them all.
Some the O rings are bad anyway and leak (older XJ) and the stock value seems to work fine.
Manual transmission often don't have the same braking problem as a slush box and work fine with whatever anchor your using.

There are 3.4 million XJ and DRIVERS on the road and everyone of them is different.
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  #8  
Old March 12th, 2008, 12:07
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Re: ZJ Proportioning Valve

I did a 8.8 swap in my 98 xj. I left the stock proposion valve, but notice a positive difference in brakeing. My 98 has the dual diapham booster and that might but where the difference comes in.
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Old March 12th, 2008, 12:12
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Re: ZJ Proportioning Valve

Quote:
Originally Posted by trail rate this
I did a 8.8 swap in my 98 xj. I left the stock proposion valve, but notice a positive difference in brakeing. My 98 has the dual diapham booster and that might but where the difference comes in.
Your dual booster only increases the pressure exerted on the master cylinder when you apply pedal, it doesn't affect the ratio that the proportioning valve sends fluid to the brakes.
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  #10  
Old March 12th, 2008, 14:17
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Re: ZJ Proportioning Valve

I threw a Dana 44 outa an XJ into the rear of my 96XJ and added, among other things, disc brakes from a crown vic. I had heard about the proportioning valve thing, but after test driving it I was happy with the way it was. Braking is much better than with the drums. I can't complain. If I didn't like it, I guess I would switch the proportioning valve, but I'm happy the way it is. The braking feels even, and I stop more quickly and with less pedal effort!! With the drums, a few days after a fresh adjustment I could tell that the fronts were doing all the work again! I don't get that feeling anymore.

My advice to anyone would be to run the current proportioning valve and see if you like it. If you don't like it, then worry about changing it.

You said that you're not happy with the improvements. Are you sure that you've bled the system alright?? Gotta start with the right rear and go from there. Sure your front brakes are working properly too?? Maybe the pads and rotors just need time to get broken in??

Last edited by mjma; March 12th, 2008 at 14:20.
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  #11  
Old March 12th, 2008, 14:17
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Re: ZJ Proportioning Valve

I compared the ZJ prop valve to my 96 prop valve and the only thing that was different was that the ZJs spring was 1/2" shorter than the XJs, so I swapped it over to the 96.
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