Rear disc conversion, Proportioning valve question??

[Harvo]

Missed the question. Mine is a 93.

 

[Bent]

My '01 had ABS prior to putting Explorer discs in the rear. No problems with the bias as far as I've been able to tell. I so far have left the ABS carp in place. Up front the brakes remained OEM. IIRC, the late model hardware handles the swap w/o any further changes. I'd have to search ModTec again to find it to be sure. Keep in mind that four wheel discs will have a slightly different pedal feel to them.

 

[johnsoninc86]

I did the zj disc swap on my 98 w/ 8.25 and my 32's lock up before the fronts. I took out just the o-ring in the prop valve. It's a little wierd feeling the rear end want to swing around in front of you, but as long as you expect it, its okay, and it still stops on a dime. It's kind of getting on my nerves, thats why I've been watching these threads. I might try the adjustable prop valve from Summitracing and see if that helps at all. If not, then back to the junkyard for a zj proportioning valve.

 

[vetteboy]

I did the zj disc swap on my 98 w/ 8.25 and my 32's lock up before the fronts. I took out just the o-ring in the prop valve. It's a little wierd feeling the rear end want to swing around in front of you, but as long as you expect it, its okay, and it still stops on a dime. It's kind of getting on my nerves, thats why I've been watching these threads. I might try the adjustable prop valve from Summitracing and see if that helps at all. If not, then back to the junkyard for a zj proportioning valve.

With all the ZJ braking equipment, I've found that I can lock up all four 33x12.5s, and the fronts lock before the rears do. The pedal modulation is pretty damn good too. With the adjustable valve I'd imagine you can tweak it to whatever feels comfortable to you.

 

[johnsoninc86]

has anybody ever put an adjustable on theirs? If so, how hard would it be to install. I thought i read somewhere that they needed different fittings in order to fit the thing.

 

[Slonopotam]

How do you understand your brakes are well balanced ? Is there a test procedure "for dummies" written somewhere ?

Thank you

 

[johnsoninc86]

the easiest way is to go out on the road when its wet, and see which set of tires locks up first. Usually, people get their "bias" numbers from when they get the vehicle inspected for some states. Being in IN i dont have to worry bout that.

 

[Goatman]

How do you understand your brakes are well balanced ? Is there a test procedure "for dummies" written somewhere ?

Thank you

Get on a dirt road, stick your head out the window so you can see the tires, and slam on the brakes. Look to see if the front or back locks up.

 

[Roxtar]

Settle down. It was an off handed comment about your originallity. Its not a bad thing. I do appreciate your comments, thats why I asked. I was just saying that its going to be difficult to come up with a definate answer because there will be so many different combinations.
Hugs and kisses.

That's the problem with questions like this.
It depends on many variables.
For instance; Explorer rear discs have very small single piston calipers. Crown Vics may have (I don't know) large twin piston calipers. 1 ton D60s might have 4 piston calipers. Each would work very differently since the brake fluid supply needs are so different.

 

[Tally_XJ]

I did the '96 ZJ disc swap on my 1989 XJ after I swapped the turdy five for an XJ D44.

I only used the ZJ rear discs, calipers, e-brake hardware and rubber hoses. I left the stock prop valve on there. I also still have the stock XJ booster and master cylinder.

I first left the (stock XJ) proportioning valve alone and got very little rear braking power but had a good hard pedal. I then removed the prop valve piston seal and got slightly better rear brake power, slight change in pedal feel. I still wasnt able to get the power I wanted from the rear brakes while running 33's. I replaced the prop valve piston seal and replaced the master cylinder (with a rebuilt stock unit). Still not good.
I again removed the prop valve piston seal and spring. Nothing really changed, however, somewhere along the line I started getting a really spongy pedal. Pedal feel is just lousy.

So, I started playing with different master cylinders (all with the prop valve piston seal and spring removed).

I have tried the E350 master cylinder, not good at all, the F250 master cylinder, no good either, and finally dropped to an F150 master cylinder that has a piston bore of just 1/8 or 1/16 inch larger than the stock XJ master. Pedal is still lousy and spongy even after six months of occasional bleeding. It feels as if the rear caliper pistons have to travel out too far to make pad contact to rotor. Pumping the brakes helps, but not much. It it is air, I certainly CANNOT get it out.

I have replaced the pads with a better brand, turned the rotors, checked for caliper alignment and have gotten no better results.

My next shot is gonna be to replace the master cylinder and booster with the new 2001 model units I have and get either the ZJ prop valve or a Wilwood adjustable prop valve.

 

[mmmkay325]

I have a 96Xj w/ abs and d35....put a d44 in the rear out of 87xj, swapped out the drums for 97zj discs. Drove it like that for a year. Never really happy w/ brakes. Seemed to glide more to stop than stop, so i swapped out a ZJ proportionaling valve meant for disc all around, that was the ticket!!!...made a hell of difference. So i'd so go that route and see if your happy.

 

[falcon556]

I have a 96Xj w/ abs and d35....put a d44 in the rear out of 87xj, swapped out the drums for 97zj discs. Drove it like that for a year. Never really happy w/ brakes. Seemed to glide more to stop than stop, so i swapped out a ZJ proportionaling valve meant for disc all around, that was the ticket!!!...made a hell of difference. So i'd so go that route and see if your happy.

The factory spent a lot of research time and money to get together parts that are balanced.
Using the original parts to stay as close as possible to the original, makes sense.
Removing o rings or using mixed parts doesn't.
BTW one of the things I really liked from the conversion is the parking brake.
Chrysler really hosed their customers by offering drums only in the XJ.
The very fact that we, without the factory resourses can modify our XJs to discs shows that they could have offered them easily. Instead basic items like select-trac were more available in the ZJ and discs were ZJ items only.
They were forcing us to buy the ZJ that cost more.
Dirty bas$$$$s.

 

[Art Triggs]

I did a zj swap onto an 8.25 this summer, (yeah, polishing a turd...;-)) I havent changed out the prop valve yet, it is a little soft, but the couple emergency/quick stops I've had to make since then have done just fine. I will probably try to adjust it a little more this spring when its warmer.

 

[natep1]

00XJ, 30's, 8.25.
GC rear setup, stock m/c & booster, adjustable prop. valve.
Stops greats, great bias.

Wish I would have put the valve on when I first did the coversion.

 

[dfreeman616]

as i understand it, removing the 'o-ring' (piston seal) effectively converts the split brake system back into a single hydralic system, so that rather than having seperate hydralic power for front and rear, they are the same. thus, the system that was designed to allow the brakes to still work with a partial hydralic falilure will no longer function at all if there's any problem (such as a torn brake line). the point of doing the disc mod is to provide better brakes, so why would you then want to downgrade part of the system? it seems like a really bad idea to me.

 

[Powerman]

Can Someone tell me this: I have a 2000 w/ ABS. Will be putting axle with disks in rear. I have a prop valve and MC/booster from a 98 Grand that had 4 wheel disks.
1. Are the MC/boosters the same in new Grands and XJs. Is mine the same as the 98 MC/booster in my garage?
2. Should I remove the o-ring in my prop valve, or use the prop valve from the 98 Grand that had disks.
Will be ripping out ABS and replacing lines soon, so anything else will be simple.

 

[falcon556]

Can Someone tell me this: I have a 2000 w/ ABS. Will be putting axle with disks in rear. I have a prop valve and MC/booster from a 98 Grand that had 4 wheel disks.
1. Are the MC/boosters the same in new Grands and XJs. Is mine the same as the 98 MC/booster in my garage?
2. Should I remove the o-ring in my prop valve, or use the prop valve from the 98 Grand that had disks.
Will be ripping out ABS and replacing lines soon, so anything else will be simple.

From what I know, the 2000 XJ and the 98 ZJ have the same MC/Booster.
If the ZJ prop valve is good as is for a ZJ with discs, why would you have to do anything? I'd say don't change anything.

 

[Slonopotam]

00XJ, 30's, 8.25.
GC rear setup, stock m/c & booster, adjustable prop. valve.

Which year did you take the rear from ?
Was the switch difficult ?
I guess 30s means rear calipers fit inside 15 rims.