Here's my situation in a nut shell...

Vehicle: 2000 XJ Sport, 4.0, Auto (AW4), NP242 SYE, D35 w/ ABS and drum brakes.

Axle: 97' Chrysler 8.25, non ABS, ZJ disc brake conversion.

I removed the D35 and swapped in a C8.25. while I had the axle sitting I converted it to disc brakes using everything off a 96' Grand Cherokee with a D44. unsure but I believe it had ABS on the D44.

Problem: after swapping the rear I changed out the XJ proportioning valve to one from the same ZJ. I read that you need to use the block off valve from the XJ and use it on the ZJ p-valve. I pulled all the fuses for the ABS (motor, light, and control) bled the brakes and still the peddel goes right to the floor. heavy braking the Jeep comes to a pretty good stop but doesnt lock the tires or cause a skid. Under light braking the peddel goes to floor and the Jeep comes to a slow stop.

Cant seem to figure out exactly where my problem is and how to fix it. how do i figure out if the p-valve is bad?

Sound i go back to using the factory XJ p-valve?

 

I never swapped mine out just used the disc. They made a little noise because they held pressure all the time but I only heard it when riding next to a wall. Mine stopped great.

 

I would put the XJ prop valve back in and bleed the brakes again, including the front ...Some people say to change the valve to ,but I've seen alot of guys don't change it and it worked just fine...

 

Ok I'll try that and see what happens. Thanks for the help!

 

Ok so today i changed out the ZJ prop-valve and went back to the original XJ prop-valve. Brakes still not holding pressure and only the fronts are locking up without a problem. i jacked up the rear and hit the brakes (foot to the floor), rear wheels just spin away.

Does the ABS pump have anything to do with my problem? assuming it was designed for 4 wheel ABS and now i only have front ABS.

 

I'm sure about one thing, switching to rear discs from drums will require a proportioning valve adjustment.
If the XJ valve is not adjustable, then the ZJ valve used for 4 wheel discs should work.

Drum brakes & disc brakes require different pressures.

Are you absolutely sure you bled ALL the air out of the system?

 

Stupid answer but are the calipers on upside down? If they are it wont hold pressure the bleeder has to be up

 

Wow for a minute you had me thinking I probably pulled a stupid move by installing them wrong but they are on the correct sides. I was reading up on the abs pump and if air gets in then a DRB II/III is needed to get all the air out. Maybe this is my problem?

What about totally deleting the abs and running the lines to the front and rear from the proportioning valve?

 

This is true and definitely not cheap to do. I came across this problem and since I'm not a big fan of ABS anyway I just removed the ABS pump bled the whole system and now all is well.

 

if you have abs you need to remove the abs unit from the system if its no longer in use, it may be holding air in the unit. I would get the lines from a non abs that go from the master to the p-valve. and if it wont have a good pedal then. you may need an in-line residual pressure valve for the rear brakes to hold extra pressure

 

If I pull abs pump how do I know which lines to connect them to coming off the p-valve? The p-valve has 2 lines coming from the top and 2 lines coming out the bottom and all 4 going to the abs pump but the pump only has 3 lines coming out of it. Tomorrow I can get pics if it makes it easier to explain.