Reality Check Rear Braking Power

D

Desert4x4

New member
Ok, so I just replaced the pad and rotors on the rear of my 1999 XJ. When I have the rear of the Jeep in the air and the Jeep running in drive 1st gear it can barely hold the rear wheels stopped. If I throttle up slightly the wheels will spin no matter how much force I apply to the brake pedal. Is this normal? My XJ has 5.13 gears and a KJ rear disc conversion.


Thanks.
 
X

xjnp242

New member
Doesn't seem normal to me.
Maybe the stock rear drum proportioning valve is not compatible for the rear disc conversion.
More than likely, could be the proportioning valve piston is stuck for the fronts only thinking there's a brake line leak to the new rear calipers.
Or the rear calipers were not bled properly.
 
R

RCP Phx

New member
The only thing I did on my 2000 was change to a Durango master cylinder, IIRC it uses the same proportioning valve as the late ZJ.
 
D

Desert4x4

New member
RCP Phx said:
The only thing I did on my 2000 was change to a Durango master cylinder, IIRC it uses the same proportioning valve as the late ZJ.
Click to expand...

I also switched to the Durango MC. It did seem to help a little bit, but I never changed the proportioning valve.
 
techno1154

techno1154

NAXJA Member
NAXJA Member
Desert4x4 said:
Ok, so I just replaced the pad and rotors on the rear of my 1999 XJ. When I have the rear of the Jeep in the air and the Jeep running in drive 1st gear it can barely hold the rear wheels stopped. If I throttle up slightly the wheels will spin no matter how much force I apply to the brake pedal. Is this normal? My XJ has 5.13 gears and a KJ rear disc conversion.


Thanks.
Click to expand...
Take your XJ out on the road and see how it respond. Try some panic stops on wet road. The rear of the XJ is lite so the rear wheels lock up easily on wet road.

My XJ have always exhibited the same traits as your XJ. With the rear wheels lifted off the ground and idling in gear, it take more than the usual amount of pedal pressure to stop the wheels from turning . This is true both with drums and discs. I tried to increase the pressure to the rear wheels which resulted in the rear of the XJ trying to pass the front when stopping quickly on wet roads. Make certain the brakes are in a good state of repair.
 
5

5.9longarmXJ

New member
If you changed to a Durango master cylinder, then you now have the Durango proportioning valve. I believe the Durango has rear drums (depending on year) the 1999 and 2000 were rear drum. So you haven't helped your rear brakes (they are not getting enough fluid). You need the proportioning valve from a grand cherokee with 4 wheel disc brakes.
 
X

XJlimitedx99

New member
I also have KJ discs and I swapped in a ZJ proportioning valve with the factory MC on my 1999. Through all my research on the swap I actually never read of people going with a Durango MC. The ZJ prop valve makes sense to me because they are similar vehicles but the ZJ has rear discs.

My XJ will just barely drag the rear tires (35s) on dry pavement. Like they won't lock up and squeal but I can tell they're on the edge of losing traction. Not sure that I've tried a panic stop in the rain before.
 
S

SlowXj

New member
Being the lazy person I am I did nothing to the brake system when I upgraded to the 8.8 disks. Unloaded the rear locks up to quick, but since I put tools, spares, etc in the back, it breaks perfectly square. Panic stop locks all 4 at the exact same time every time... I would bleed the system again. That's the easiest place to start

Sent from my SM-G950U using Tapatalk
 
R

RCP Phx

New member
5.9longarmXJ said:
If you changed to a Durango master cylinder, then you now have the Durango proportioning valve.
Click to expand...
I'd like to hear the logic in that?

It does matter the MC diameter, based on year they are different sizes. I went with the larger one because I also installed WJ fronts.
 
denverd1

denverd1

NAXJA Member
NAXJA Member
going to D44's with chevy calipers in rear.

Heard about Dodge 2500 M/C and prop valve as the go to swap. Brakes are so far off, I haven't researched them much. anybody using much bigger M/C?
 
clydefrog

clydefrog

NAXJA Member
NAXJA Member
Was this right after doing the brakes? Or where they properly broken in first? If you did the pads and rotors and DID NOT drive it afterward and it did this while still on the lift I would consider this normal.

Just thought I would ask the question no one else was before we try to land the space shuttle.

If you did break in the brakes first then ignore what I just wrote...
 
egon

egon

Dunlop Slayer
NAXJA Member
I was one of the first to do a KJ rear disc swap. Did the ZJ proportioning valve first which was ok with 33s. Beyond useless with 35s. I changed to a 1995 E-350 master and booster and no proportioning valve. As close to perfect as I could want.

--Matt
 
You must log in or register to reply here.
Top