disc brake swap help

so the jeep is a 93 cherokee country that originally had a dana 30 and and a dana 35 in it with abs, well a couple months ago i swapped an xj dana 44 from the junkyard in it but i couldnt get the brake drums to stop dragging. over the weekend i swapped in disc brakes from a 8.8 everything is brand new from the axle shafts seals and bearings to the calipers but for some reason i cant get a decent pedal out of it. A 10 mph roll and it wont even lock up the tires and it barely locks up the front in lose gravel. ive bleed the back serveral times and its just coming out straight fluid it we do the traditional bleeding technique. and ive tried using my pneumatic bleeder but it leaves me with mixed results so im not sure. it seems like the whole system is not getting enough pressure. we tried to put the jeep up on jackstands in the back and hold the brake to see if it would stall it (its a manual) but with the slightest amount of throttle and the pedal to the floor it just powered right over the brakes.

if you guys could give me any ideas as to what to try, id really appreciate it

sounds like you still have a air bubble in the system. also did you do anything to the proportioning valve? you either need to swap one in from a disc braked ZJ or take the valve out for the rear brakes altogether. rear discs require more volume than drums so that might have something to do with it too

They will work okay without the disc brake prop valve, just perform better with it.

And, don't change the whole prop valve. Just the guts.

You don't have the calipers on upside down with the bleeders o the bottom, do you?

When you swap out the prop valve guts do you need to re-bleed the system and/or does it cause the Master Cylinder to drain all the fluid out the front when you swap the guts out?

yes you would need to re bleed all four corners

I didn't swap the prop valve, I thought that only change the pedal after half travel (emergency braking) and I thought maybe my master cylinder was failing as I started getting a soft pedal a couple days before the swap

Some find they need to swap the guts, some find they don't. I was lucky and didn't need to. I would swap the piston and spring first before condemning the Master. If that has no effect after a rebleed ... Then start looking at the rest of the system.

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BossCherokee95 said:

I thought maybe my master cylinder was failing as I started getting a soft pedal a couple days before the swap

Click to expand...

Would have been nice info for the first post. Sounds like MC time.

Really sounds like you still have air in the system somewhere. At work I've swapped countless 8.8s into what were originally drum D35s without issue, the prop valve will just help give more force to the rear but is by no means necessary.

Did the master run out or low on fluid while you were bleeding by chance? If so you may need to "bench bleed" the master as well as bleed the whole system. In what order are you bleeding? Should be from the farthest from the master to the closest. And as mentioned, your calipers aren't on the wrong sides with the bleeders on the bottom are they?

I ran mine with stock guts for a while. Swapped for the later guts and noticed an improvement.

No it didn't run out I had my buddies topping it off as we went. The prop valve change wouldn't change the peddle feel with the engine off would it? Also is there anyway to test the mc before I condem it btw my abs not being activated would affect performance would it?

As said above, swap out the prop valve (Or just the internal parts) with one from a rear disc brake ZJ, Then read the last couple of pages of this thread, follow the recommendations on properly bleeding the prop valve & your problems will be solved.
http://www.naxja.org/forum/showthread.php?t=1124404&page=13

Good Luck!

cruiser54 said:

I ran mine with stock guts for a while. Swapped for the later guts and noticed an improvement.

Click to expand...

I swapped my rears to discs but haven't swapped the guts on my Master Cylinder yet... perhaps I should do that. I have the guts for the swap, but since my brakes seem good I never finished swapping in the 'guts' designed for rear discs.