I know that you figured out that your problem was swapped calipers and this thread is old now but i have this same problem with my 87 xj. I took out oring inside valve just so i would have full braking power but i talked to one of the old mechanics at my work about this.
He told me that you have to push the valve back to the center of the housing, said youd feel it seat in place. He said he used to use a nail that would fit thru the hole on the front bleeder to push it back to center, then when he was done bleeding he would c if the valve moved and go back to the rear to make sure fluid was still flowing to the rear brakes. I am going to try this this weekend i will let you know what happens for future issues that may arrise.
And where did you get a comb valve from by the way? my local parts stores said they didnt have them, did you have to go to dealer?

 

I believe GC discs are dual piston and bigger rotors where as xj calipers are single and smaller...i could be wrong tho

 

WJ Grand Cherokee's are dual piston/ bigger disc, ZJ Grand Cherokee's should be single pistons like the XJ.

 

Yes to both. Dealer for combi ( HIGH DOLLAR) and dual piston bigger rotors. Still having a few issues but normal compared to the other brake problems I was having. Just need to replace bleeders on front calipers and get them bleed good.

 

UMMMM OK so what do I have then? They are dual piston and rotor is about 3/4 to 1 inch bigger. Explorer?

 

ok cool thx. i guess if what my coworker said doesnt work i will just have to go buy one how much was that part where ur at by the way? everything seem so be more in hell on earth! lol

 

If I remeber right it was like $140 more than twice what a new mc runs. lol

 

HOLY CRAP!!!!! that sucks for me! but maybe not i know its too late for you but check out what i just found.....http://www.carolinaclassictrucks.com...rop-valve.html
Ill have to double check mine but from what i remember this looks exactly like it for $80

And also one other thing i am gonna look into is trying to find the GM counter part of the JEEP valve since jeeps had FORD DODGE and GM parts back when mine was made lol. it might be even cheaper than this one.

 

http://www.4x4wire.com/jeep/tech/bra...rakes03/47.jpg

XJ vs WJ brake caliper *there are 2 versions of the WJ caliper but they look similar*. Explorer Sport Discs are the basically the same discs as a WJ. Different lug pattern and a slightly different offset.

If you take a picture of the front brake setup, I should be able to tell you if you've had the WJ swap.