8.8 swap brake issue, any ideas?

mileshigh

Well-Known Member
Joined
May 2, 2005
Location
Charlotte NC
Ok so i swapped a 98 8.8 in my 1990 Xj jeep and put new rotors,pads,calipers on it,new hard and rubber lines. Along with putting all new brakes on the front dana 30. I bleed them and only had about 1" of brake pedal! So i replaced the master cylinder and brake booster with one from a 1994 Xj since i had the parts. Still the same problem...then i took the rubber o-ring out of the stock proportioning valve to see if that would fix it and still nothing. I can push the brake pedal to the floor and hold it and then push the gas and the jeep will power brake and stay still while the rear wheels spin. So i know the brakes are working and that the rear brakes provide all the pedal feel..so the last thing i can think to do is get a grand cherokee proportioning valve but i wanted to see what others had to say before i spent the money. So any ideas as to what my problem is?
 
I have a 1995 YJ with an 8.8 with discs and Dana 30 front. I didn't have much brake at first either when I put the 8.8 in. Many scary stops later, I installed a brake master cylinder from a 1985 Ford E350 van and removed the stock proportioning valve and installed an adjustable proportioning valve. I have much better brakes now. The master cylinder from the E350 looks identical on the outside to the YJ MC, but the piston is larger in diameter. It seems like the MC was around $25 or so and the I don't remember what the adjustable prop. valve cost.
 
go to the junkyard and get the booster and MC out of a 96 cherokee. The master cylinder can come out of anything newer, but the booster needs to be the dual diaphram one out of a 95 or 96. Will give you the extra power you need.

Also, when I did my brake swap I bought a cheep vacuum pump from harbor freight and vacuum bled the lines
 
Just for kicks, make sure you have the calipers on the right sides. I've heard (cough cough) some people have put the right caliper on the left and the left caliper on the right. When you do this, the bleeder ends up being at the bottom of the caliper and you can't get all of the air out. I've, err someone else, did this twice.:shaking: I hope you're not as dumb as that guy.
 
Brett,
Your XJ had drum rears and now you have disc rears.
Disc brakes require a much higher line pressure than drums.
The stock proportioning valve is designed to regulate pressure for rear drums, ditch it.

Thats why the front is stopping fine, but the rear is spinning through the brakes. The fronts have adequate line pressure and are working right, the rears need more fluid/pressure.

Now you could be cheap, save a few dollars and try several distribution block/prop valve combos and aggravate the hell out of yourself, OR you could drop $100 and get an adjustable proportioning valve from the start. (Not that I have ever tried to take the cheap way out or anything...)
 
had the same problem with my yj. i went with a grand cherokee master and an adjustable valve. stops good now but i would try no valve because i have mine adjusted almost all the way out.
 
If you do the dual diaphram Booster swap 97 is the most compatible swap. You can find all the info on NAXJA for that swap. It has something to do with the way the puchrod bolts in and the length it will have and the bolt holes lining up. I wanna say that with the 97 you only have to ream out the hole that the pedal connects too. I don't think I have the write up and more. i will have to look as I need to do the same swap. I did go and get an E350 MC since I have a 44 and 9" sset up now. I just haven't put it in yet. Good luck
 
I would think that it is the proportioning valve not the master cylinder or booster, I did the d44 9" swap, and my brakes work great. I left the drums in the rear and all brake system is stock other than the axles. I've heard that a proportioning valve from a Rubicon works when converting to rear discs.
 
yea so putting the calipers on the right side and installing a grand cherokee proportioning valve makes a hugh difference...no more power braking!! P.S. if anyone ever gets asked to change a proportioning valve just say no!!
 
mileshigh said:
yea so putting the calipers on the right side and installing a grand cherokee proportioning valve makes a hugh difference...no more power braking!! P.S. if anyone ever gets asked to change a proportioning valve just say no!!
Click to expand...
I knew your problem sounded all too familiar to what I did. I guarantee the calipers being on the wrong sides was more of a problem than the prop valve. Just learn form your mistake and don't do it a second time like I did.
 
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