winginit

Just a little food for thought

The rear output includes a 10lb residual valve that is required to keep the shoes close to the drum, but with discs may cause the pads to drag a little

Combination valve - the stock valve is not just a proportioning valve, but also a metering valve.

"A metering valve or "hold off valve" is used in the disc portion of a disc/drum system to hold off the application of the front discs slightly allowing the slower reacting rears to catch up. This provides rear stability on wet surfaces and reduces excessive pad wear. "


Having said all that - it will work, but you sure won't get the braking you paid for with your 4 wheel disc swap.

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bad_idea

Thanks winginit, you proved cruiser right again. Now I have more questions. I am now planning to use the WJ booster and mc w/ the ZJ guts. Are you saying there is issue with that winginit?

cruiser54

That's what works. WJ and ZJ 94 to 98 had rear discs. Have the proper residual valve. Add the prop valve guts and you're in good shape.

winginit

Well their you go, cruiser is right again !!

rcguymike

So does the brake booster have to get swapped to get the right residual valve? Or is that function part of the proportioning valve on the ZJ's?

cruiser54

Technically, yes.

Practically, no.

Just do the prop valve guts on your 99.

rcguymike

I have a '96 v8 parts ZJ I'm planning on stripping. Is it worth swapping that brake booster? What do I loose by just using the prop valve?

cruiser54

That booster/master doesn't work. Grab the prop valve guts though.

rcguymike

So what function(s) would I still be missing by just swapping the prop valve? Planning on 35's someday so maybe I should upgrade the brake booster?

cruiser54

None.

You only swap the prop valve guts if you go rear disc brakes.

YOu already have the booster you need in a 99.

rcguymike

What about the residual valve winginit mentioned? Is that prematurely wearing the rear brakes and rotors?

It seems like a lot of people are upgrading to the WJ brake booster and removing the proportioning from the prop valve once they have 33's or larger?
http://www.jeepsunlimited.com/forums...-Clarification
And
http://www.4x4wire.com/jeep/tech/bra...rakes03/valve/

Edit: or is that mostly for the older XJs?

cruiser54

Just do the rear discs with the prop valve guts mentioned......

rcguymike

Ok just to finally beat it into my head... What exactly does the ZJ prop valve do that the '99 XJ one doesn't and why are some people modifying the o-ring when they get bigger tires? Wouldn't that make the front to back bias closer to 50/50ish?

EZEARL

I can't address the bigger tires issue. I ran the XJ p/v guts for a week or so with no problems but it felt like I was getting 50/50 distribution. When I installed the ZJ guts I could feel a difference in that the front were being applied first. I do know that 2 weeks ago I had to come down on the brakes HARD when doing 35mph when a dog ran out in front of me. Got stopped with complete control. I have wondered though what it would have been like with the XJ guts.

cruiser54

The ZJ came with rear discs and the 99 xJ didn't.

Why don't you study it and give us a term paper on it by the end of the week?