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crown vic discs on d44...need advice

T

Tre

NAXJA Forum User
Location
canada
Ok well the discs are on brakes are all bled.

but my pedal is still so spongy it doesn't even feel safe to drive.
its a 88xj 4.0 aw4.
now do i need to upgrade the mastercyl? or put in a different prop valve?
 
also been reading that taking the oring out of the stock prop valve should fix it as well.

can someone that has done the crownvic discs let me know asap.
 
well i'm not sure spongy is the correct term to describe it.

its more like the pedal doesn't do anything until its almost at the floor.
with the jeep off i can pump the pedal and it builds pressure. but as soon as its on it just goes back to normal and doesn't activate the brakes till its near the floor.
 
nobody thinks that i need to swap to the newer style master cyl?
as well what about removing the oring in the prop valve like i've beenr reading?

or are those just 2 things to help better the braking performance? not necassarily meant to correct the need for a air free system.
 
Tre said:
or are those just 2 things to help better the braking performance? not necassarily meant to correct the need for a air free system.
Click to expand...
Correct. Having a newer m/c will help with braking performance and will give you the peace of mind of having a newer master cylinder..

Doing the prop valve thing, will help stop the rear wheels from locking up after installing discs in the rear.

Neither really don't have anything to do with air in the lines. From the symptoms you described, it sounds like you still have air in the lines. Bleed the crap out of them and make sure you do it in order. You may have to do the whole thing a few times depending how much air is in the lines.

I use a vaccum hand pump that I bought for about $60. I really like it because you can do it by yourself and it saves the wife's leg from cramping up from having to pump the brakes soo much.. :gee:

Elias
 
well think i found partially what my problem is. turns out i may have overlooked which way the calipers go on. i got them upside down with the bleeders on the bottom.
 
That would probably be 100% of your problem. You have calipers full of air. I would not mess with the prop valve until you get it properly bled and see how the front-back balance feels. If you need more braking power to the rear, pulling the o-ring from the prop valve is one option.
 
exactly what i'm gonna do man. i haven't touched the prop valve yet. i was just under it this morning cuz last night i had one of those moments when your laying in bed thinking about jeeps. and well it hit me that i wasn't paying attention to the bleeder position on the calipers. sure enuff i go out and found they're on the bottom. so i gotta flip emm around now.
 
just a update. i finally got around to flipping the calipers over. so they're the right side up.

bled them out. now the pedal is back to 100% normal. and the brakes are very sensitive now. doesn't take much pedal pressure to stop in a hurry.

i do notice though that the rears seem to be dragging a little bit. Is this due to the prop valve being the original from the drum seutp before?
 
is there a diagram i can view to see what exactly i gotta remove and do?

i know where the prop valve is and what it looks like. just havne't torn it down before.
 
The proper way to address front to rear brake bias, is to replace the proportioning valve. I went to a Jeep wrecking yard and paid $15 for a Grand proportioning valve, swapped the guts (mainly the spring) between the two and re-bled (you'll have to bleed it all over again). It made a big difference.---------Hans
 
Oatmeal said:
The proper way to address front to rear brake bias, is to replace the proportioning valve. I went to a Jeep wrecking yard and paid $15 for a Grand proportioning valve, swapped the guts (mainly the spring) between the two and re-bled (you'll have to bleed it all over again). It made a big difference.---------Hans
Click to expand...
thats what i was thinking of doing based on other peoples experiences as well.

I realize its a prop vavle problem. I've just never torn one down before. im interested in hearing how its done.
 
I don't think that just going to a ZJ proportioning valve is going to do it. If you were using ZJ calipers, then yes it probably would.

I just recently put a ZJ prop valve in my XJ with the Ford brakes. Initially I thought it was great, I had brakes like I never had. But and unknown problem quickly arose. Due to the differences in the Caliper Piston area of the Ford and GC calipers, the pressure doesn't bleed back correctly in relationship to the master cylinder. The pressure slowly builds up over a period of time, in my case over 5 miles, that soon the rear brakes are actually locking up. Let them sit over night, and the pressure slowly bleeds off.

What I'm presently doing, is completely bypassing the factory proportioning valve for the rear and doing an adjustable. Based on what I've been able to figure out, this should solve my problem. If not, back to the drawing board.

This is just but one of the many sites that I've been using to come up with the solution. Especially note the last page on calculating Master Cylinder/Caliper piston area. http://www.factoryfive.com/table/whatsnew/tech/brakeadvice.html

Here's another link that gave me some additonal insight. http://www.4x4wire.com/jeep/tech/brakes/yjmc/

Hope this gives you a bit better insight.

I'm not saying the ZJ prop valve won't work because there is a difference between the Crown Vic calipers you used and the Lincoln calipers I used.
 
Last edited:
rstarch345 said:
I don't think that just going to a ZJ proportioning valve is going to do it. If you were using ZJ calipers, then yes it probably would.

I just recently put a ZJ prop valve in my XJ with the Ford brakes. Initially I thought it was great, I had brakes like I never had. But and unknown problem quickly arose. Due to the differences in the Caliper Piston area of the Ford and GC calipers, the pressure doesn't bleed back correctly in relationship to the master cylinder. The pressure slowly builds up over a period of time, in my case over 5 miles, that soon the rear brakes are actually locking up. Let them sit over night, and the pressure slowly bleeds off.

What I'm presently doing, is completely bypassing the factory proportioning valve for the rear and doing an adjustable. Based on what I've been able to figure out, this should solve my problem. If not, back to the drawing board.

This is just but one of the many sites that I've been using to come up with the solution. Especially note the last page on calculating Master Cylinder/Caliper piston area. http://www.factoryfive.com/table/whatsnew/tech/brakeadvice.html

Here's another link that gave me some additonal insight. http://www.4x4wire.com/jeep/tech/brakes/yjmc/

Hope this gives you a bit better insight.

I'm not saying the ZJ prop valve won't work because there is a difference between the Crown Vic calipers you used and the Lincoln calipers I used.
Click to expand...
I really don't think that the proportioning valve would cause that sort of problem. That sounds like a residual pressure valve problem. Did you use a different master cylinder?----------Hans
 
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