Using ABS calipers on a non-ABS system

[whitetailjeeper]

I have a 1989 Jeep Comanche without ABS. It was originally 2-wheel drive, but I began the conversion process by swapping in a front axle from a 1993 Jeep Cherokee with ABS.  After that was put and the system bled  we went to test it and found we were without brakes.  The pedal went to the floor.  It could be pumped up without leaking down, but after it was let off for a few seconds, it would again push straight to the floor.  We found the proportioning valve was stuck, so it was replaced along with the weak, old master cylinder.  The height-sensing system in the back was eliminated by running a new hard line.  Also, the front axle was equipped with new calipers, rotors, pads, and flex-lines.  I have yet to find any leaks, yet the pedal is just the same.  Could it be the fact that I am running ABS calipers (which are a bit bigger) on a non-ABS system?  Or is it something else??

[Dando]

I have a 90MJ and I swapped the axle and brakes etc from my 95xj and it had abs in the XJ and not in the MJ. I have noticed no problems from running abs calipers on a vehicle without abs. I think your problem is something else, I'm just not sure where to tell you to look.

[Eagle]

Could it be the fact that I am running ABS calipers (which are a bit bigger) on a non-ABS system?

Nope.

 

Or is it something else??

Yepp.

[Rockfrog]

Sounds like you have the MJ's braking system confused with an XJ's braking system.

The MJ front proportioning valve, simply put, isn't a proportioning valve. It is merely a distribution valve. Two lines to the front as usual ... But also two lines to the rear. Where the actual proportioning valve would be in the block is the secondary line for the rear braking system. That load sensing Valve is the Proportioning valve on an MJ.

I suspect you will need to swap the stock type valve for one from and XJ and start over. Did you bench bleed the master?

[Eagle]

We found the proportioning valve was stuck, so it was replaced along with the weak, old master cylinder.  The height-sensing system in the back was eliminated by running a new hard line.

1) On the MJ, as commented above, the front thingie under the master cylinder has no proportioning function, so what on yours was stuck? How did you determine that something was stuck?

 

2) MJ front metering blocks don't grow on trees, so what did you replace it with?

[whitetailjeeper]

I did bench bleed the master cylinder, and the pvalve I replaced it with was a new xj unit, so now the brake system is nearly identical to that of an xj.

[mjeff87]

You may have your plumbing mixed up with the new XJ valve....the FRONT output line on the MJ valve feeds the rear circuit, not the line on the bottom of the valve.  That bottom line is supposed to be an "emergency" circuit that activates in the event the MJ valve fails.  When you ran the new line to the rear, which line did you replace?

[whitetailjeeper]

You may have your plumbing mixed up with the new XJ valve....the FRONT output line on the MJ valve feeds the rear circuit, not the line on the bottom of the valve.  That bottom line is supposed to be an "emergency" circuit that activates in the event the MJ valve fails.  When you ran the new line to the rear, which line did you replace?

I plumbed the rear line into the front output, as you said.