Brakes not working properly after 8.8 swap

I just finished my 97 Cherokee ford 8.8 disc brake axle swap,
Now my rear brakes aren't working properly. There is no air in the lines,
and I've already tried the O ring removal trick from the proporting valve...
and it didn't do the trick.

The front brakes engage normally, the pedal is soft
and the back calipers don't seem to be grabbing like they should.

Do I need a new master cylinder than moves more fluid?
Would a ZJ or Durango master cylinder work?

I have a trail ride Satuday and I want to get these
brakes working better so I can attend.

They stop the vehicle, but they are maybe 60% what they should be.
Again, there is no leaks, and the system is fully bled.

barillms said:

I just finished my 97 Cherokee ford 8.8 disc brake axle swap,
Now my rear brakes aren't working properly. There is no air in the lines,
and I've already tried the O ring removal trick from the proporting valve...
and it didn't do the trick.

The front brakes engage normally, the pedal is soft
and the back calipers don't seem to be grabbing like they should.

Do I need a new master cylinder than moves more fluid?
Would a ZJ or Durango master cylinder work?

I have a trail ride Satuday and I want to get these
brakes working better so I can attend.

They stop the vehicle, but they are maybe 60% what they should be.
Again, there is no leaks, and the system is fully bled.

Click to expand...

are the rear calipers seized?

You should have at least as much braking power as with the drums, even hooked up with the stock booster/MC/Prop valve, if everything else is OK.

Make sure the bleed ports on the calipers are on the top. I used the internals of the ZJ proportioning valve from a V8.

mecompco said:

You should have at least as much braking power as with the drums, even hooked up with the stock booster/MC/Prop valve, if everything else is OK.

Click to expand...

agreed, if anything the rears should lock even even easier. granted, locking doesn't cause the vehicle to stop faster, it's just a measure of the power of the brakes...

another thought too... make sure the lines aren't crimped or rusted shut. had that problem on my old 92 taurus SHO... the pass rear on those always rusts itself shut.

I swapped mine in and didn't do anything but hook up the lines. It works great. They don't drag, and to my suprise don't lock up when going down hill. I could tell a MAJOR difference when I was stopping on the highway though. Mine is a 96. I'm not sure if they changed anything on the brake booster/proportioning between 96 and 97. If anything you should be braking too hard in the rear. If your pedal feels soft, I would say they need more bleeding. I was able to use a gravity feed bleeding method on mine. Opened up the master cyl, and cracked open the valve on the wheel cyl and let it almost empty the master cyl. Fill er up again and repeat on the other side.

IH8RDS said:

Make sure the bleed ports on the calipers are on the top.

Click to expand...

x2 I made this mistake and it took me a little bit of time to figure it out. Just need to swap them side to side.

Ok, swapped a ZJ master cylinder today and prop. valve...
and it's still the same as it was.
Checking bleed ports now!

All the brakes are brand new.

bring it to a shop and get a quote.

if it's cheap enough, have them fix it, if not, you know what the problem is.

So here is the email i sent to my friend about paying him $400 to do this swap for me...

Hey whats up man, this is Eric Im the guy who bought Js XJ, i think you had the black TJ on 35s that drove him home from the bank? Anyway, I talked to him and i wanted to see if you were interested in doing an axle swap for me. I was looking at spending about $600-700 to have my 8.25 regeared but figured I mine as well just do an 8.8 swap for that price. I have tools and a rented garage right now so my drop brackets and front axle swap and 7" of lift etc is almost done, but soon I will have to turn in the keys to my storage shed and I'll have no place to work. Anyway, i can get all the parts, ZJ proportioning valve for the brakes, calipers/pads if need be, an 8.8 out of an exploder, whatever diff fluid is needed, u-bolts for the spring perches, and a Ruff Stuff Specialties 8.8 swap kit (includes pre-fabbed leaf spring mounts and shock mounts), plus the yoke adapter for the driveshaft. For $400 I'll drop the XJ off with all the parts, and you do the swap for me. It is a pretty straight forward swap, I would do it myself and just set everything up and bring the axle with the mounts clamped on to a welding shop and spend $50 max for them to run a few beads, but I have no place to do the work. I am still considering doing this on my own and just renting another garage, but $400 should be a pretty attractive deal for a weekends labor. You would also have to weld the tubes in place because they like to spin. Anyway, i got quoted $595 at a shop which is insane to essentially do no more than weld some metal. The only things that scared me away from this swap is that the mounts for the leafsprings have to on pretty much perfect, otherwise it will throw the whole rear end out of whack, that and swapping in the new ZJ proportioning valve for the brakes might be a pain.

Anyway, let me know what you think.


Then i thought, wait $400 to run a few beads???? So how hard would this to be to do this swap myself and have a shop weld it?

do you have ABS? you will need to get rid of all of it(pump) if you do because it wont work with the 8.8. Did you rebuild the calipers or did you buy those shitty refurbished ones? sounds to me like you either have a plugged line, stuck caliper or you didnt bleed you breaks good enough.

bleed bottle is your friend.

I have a 97 with an 8.8. I took the plunger out of the prop valve IIRC its been awhile. The disc brakes were a huge help for mine, it stops 10X better and has much better pedal feel as well. Its been 3-4 years now and I still think its one of the best upgrades I have done.

For what its worth my 97 Has ABS and I left all the pump stuff in there. I cut the wires off at the rear and pulled the relay for the ABS light. Other than pulling that part from the prop valve my brake system is completly stock.

jpcherokeekid said:

do you have ABS? you will need to get rid of all of it(pump) if you do because it wont work with the 8.8. Did you rebuild the calipers or did you buy those shitty refurbished ones? sounds to me like you either have a plugged line, stuck caliper or you didnt bleed you breaks good enough.

Click to expand...

My 8.8 works just fine with my ABS pump still in place with relay and fuse pulled. The problem you can get into with the pump is when it comes time to bleed the system. If air got into the pump just remove it and run some new lines. I went for NAPA rebuilt calipers because the ones that came with it were questionable and I didn't want to take a chance. When I did my swap I paid a shop about $300 to use the bay, tools and for them to set the pinion angle and burn the perches on. At the time I didn't trust my Mig welds.

~Alex

I got a guy willing to take $400 to do my swap for me, seems like a bit much but that includes everything...

emr1101 said:

I got a guy willing to take $400 to do my swap for me, seems like a bit much but that includes everything...

Click to expand...

My buddy (reelbigdundy87 - Adam) probably paid...100 maybe? That included welding the tubes to the center section. It was like an hour and a half's labor.

Adam ground and pounded the old mounts off, took the old axle out from under the jeep, I went over and we aligned the mounts while getting the pinion angle set perfectly. He tacked them into place (very basic wire feed, no gas) to keep them from shifting around. Brought them to Baystate Offroad in Middleboro, MA(Bob and Liza kick a$$!!!) and he laid some sweet beads. We even sat there and waited for it to be done. Didn't take long at all.

The more prep work you can do, the more money you'll save on labor.