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Rear disc conversion, Proportioning valve question??

Ray H

Ray H

NAXJA Forum User
Location
Falling Waters, WV
I know this has been discussed many, many times. Theres alot of info but its hard to sort through to get a definative answer. Maybe there isnt a definative answer, maybe it depends on other factors like ABS or master cyl. differences. Either way hopefully this thread will show it. Lets keep it simple, no discussion about the install or prices or ZJ/Crown Vic or 8.25/D44/D35 unless someone thinks these items effect the brake proportioning.

Whats everyone doing and how are your brakes after all is said and done?

1) Leave the pro. valve as it is.
2) Remove the O ring.
3) ZJ pro valve.
4) adjustable pro valve.
 
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I have a ZJ proportioning valve and master cylinder and booster, with ABS removed, powering a rear D44 crown vic disc swap in my XJ. According to the state DMV inspection, my rear braking bias (with 33s no less) is slightly better than stock.

I love the swap so far...it's not necessarily that it stops better...it's that I like not having the rear wheels lock up when the drums get full of mud/water, and I also like the pedal feel and modulation a lot better.
 
What year XJ? Did it have the old or new design master cyl? Im just trying to determine why you switched to a ZJ master and booster.
 
I have an '88 with the later model booster and M/C, and have Explorer rear disc brakes. Also have a D44 front with the Chevy 1/2 ton calipers.

I haven't done anything to the proportioning valve and the brakes work fine. Seem to be well balanced front to rear.
 
This thread just started and I can see already that its going to be hard to nail down the dos and donts of proportioning. What a bunch of Dr. Frankenstiens we have here.
 
Ray H said:
This thread just started and I can see already that its going to be hard to nail down the dos and donts of proportioning. What a bunch of Dr. Frankenstiens we have here.
Click to expand...

WTF are you talking about?

A couple of us have shared what we did, to add to the discussion? What's the Dr Frankenstien comment about?

I love it when people expect you to take your time to help them but then they bitch about the info you give them. No appreciation for what someone else is willing to take time to do. :rolleyes:

If I totally misunderstood you, fine, please explain.
 
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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.;)
 
Ray H said:
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.;)
Click to expand...

OK, so I'll settle down. (I just left my wife in the hospital, so I might be a little wound up). I don't want to trash your thread, it should be a good one. I still don't get the comment, though, didn't think originality had much to do with simply telling what we've done and how it worked. Mine just happens to work fine without any proportioning valve modifications, and I've talked to others with the same experience, so I thought it was applicable.

No need to explain any further, let the thread get back on track.
 
Goatman said:
OK, so I'll settle down. (I just left my wife in the hospital, so I might be a little wound up). I don't want to trash your thread, it should be a good one. .
Click to expand...

thanks. I understand and am sorry to hear about your wife. No hard feelings what so ever.
 
After I installed my 8.8 with discs, the braking was horrible. I removed the o-ring and it stops significantly better, but the rears are getting too much fluid and locking prematurely. When I have the time I'll put in a newer XJ booster and MC, and GC(4 disc) prop valve.
 
I did the grand swap, on a 98 8.25, left the prop alone, and braking is excellent. I am on 35's
 
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I look at it this way, do the disc swap and drive it. If it feels fine, then good. If not, then move on to removing the o ring. If it stop fine, good, if not, then look into the other issues. I don't think any will be "dangerously" bad, so just like building your own rear spring pack, it may take a little trial and error.
 
My stock 97 MC and Proportioning valve works fine. It stops when it needs to and will stay locked when holding it on an incline.
But of course for this discusion some specs are going to be useful,Veh wieght, tire size etc. These will also make a difference in the performance of the brakes.
On The street my 33's would slightly lock up but my 35's haven't yet.

Btw I haven't removed the O-ring.
 
I did the swap for Grand brakes. First I took out he oring. With it out, I couldn't stop the rear wheels at all in drive with the XJ up on jack stands.

I put it back in like it was originally and the brakes are great. More rear stopping power, maybe more rear bias than before, but my fronts still lock up first.

It was an amazing difference to me the first time I stepped on the new brakes driving down the road. Soooo much stopping power!!
 
JnJ said:
I look at it this way, do the disc swap and drive it. If it feels fine, then good. If not, then move on to removing the o ring. If it stop fine, good, if not, then look into the other issues. I don't think any will be "dangerously" bad, so just like building your own rear spring pack, it may take a little trial and error.
Click to expand...

Thats probably what I'll end up doing. Ive been researching and read the writeups and it seems strange that some people say their performance got worse until they modified their prop. valve and others say no problem the way it is. Im just trying to determine if thats because of changes in the valves or master cyl over the years.
Ive got a D44 with big drums in the garage waiting to be locked and regeared and Im only going to 31s, maybe 33 years down the road. Im not even sure if I want to mess with discs for now if it envolves rebuilding most of the brake system. Ive never had an issue with my stock brakes on 30s but ive also got a 96 which has a better booster and master cyl than alot of the older XJs. My main reason for considering disc now is that I hate working on drums.
 
Harvo said:
I did the swap for Grand brakes. First I took out he oring. With it out, I couldn't stop the rear wheels at all in drive with the XJ up on jack stands.

I put it back in like it was originally and the brakes are great. More rear stopping power, maybe more rear bias than before, but my fronts still lock up first.

It was an amazing difference to me the first time I stepped on the new brakes driving down the road. Soooo much stopping power!!
Click to expand...

Harvo, what year is your XJ?
 
Harvo said:
I did the swap for Grand brakes. First I took out he oring. With it out, I couldn't stop the rear wheels at all in drive with the XJ up on jack stands.

I put it back in like it was originally and the brakes are great. More rear stopping power, maybe more rear bias than before, but my fronts still lock up first.

It was an amazing difference to me the first time I stepped on the new brakes driving down the road. Soooo much stopping power!!
Click to expand...
Question: When you removed the o-ring (which isn't really an o-ring, BTW) ... did you also remove the spring, or did you leave the spring in the valve?
 
I removed the spring also... but put it back in after I saw the results were crap.

At least I'm pretty sure that's it. It was a year ago and ive slept since then.
 
Ray H said:
What year XJ? Did it have the old or new design master cyl? Im just trying to determine why you switched to a ZJ master and booster.
Click to expand...

'94 XJ, later model so it was the new design. It was shot anyway though, and I got all the ZJ hardware for free.

Originally it was just going to be the master and prop valve, but the pushrod length was different between the old booster and new master and I didn't feel like messing with that, so I just swapped everything in.
 
I used all ZJ parts including the valve.
It feels good on braking and they don't grab when wet like the drum POS brakes my XJ came with.
 
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