• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Reality Check Rear Braking Power

Desert4x4

NAXJA Forum User
Location
Phoenix
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.
 
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.
 
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.
 
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.

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.
 
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.
 
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.
 
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
 
Just because it happens, do you have the calipers on the correct side?
 
If you changed to a Durango master cylinder, then you now have the Durango proportioning valve.

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.
 
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?
 
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...
 
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
 
So for an update: I completed the front brake replacement. New bearings, seals (Spin-Free kit) machined rotors and pads. So now in total, all brake pads, all rotors and the master cylinder (Durango 1999) is brand new. The master cylinder was bench bled, installed and the system was bled as well. The Jeep just seems to have terrible stopping power. It definitely cannot lock the tires on dry pavement. Slamming your foot on the brake pedal is more like a standard quick stop. Is this just normal for the weight of my Jeep and the size of the tires? My last weigh was 4825 lbs.
 
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


Do you think the removal of the proportioning valve or the different master cylinder made the most difference?
 
Back
Top