Well, if it's the bendix system I'm thinking of, pump and accumulator is over on the passenger side of the engine compartment. Follow the brake lines along the firewall to it.
You have to remove the entire system and replace with non-ABS parts. Master cyl and vacuum booster from a non-ABS jeep. Can't just yank the fuses and relays like you can with later ABS versions, that will disable your power assist.

 

????

Did you adjust the rears after you installed the new rear brake shoes.

 

Could be the pump had already failed. It's a crappy ABS system.

 

Not sure it matters, but here's how I got here. I had a Dana 30 and a c8.25 from a non abs jeep that I put gears and lockers in but the jeep was totaled. So I kept the axles and bought another Cherokee, '91 Laredo with the abs system. The Laredo ran great before swapping out the axles. But now is a different story with the upgraded non abs axles.

So the plan for tomorrow is to track down this pump system and replace it with a non abs master cyl and vacum system, sound good??

 

Perhaps this will be helpful:
http://www.naxja.org/html/techarticl...ll_OEM_ABS.htm

 

So I got something else that might help. When I did my back breaks. I let the jeep sit over night and by morning had no pressure again. What I found was 1 of the bleeder values was leaking. I spent $1.50 at auto zone and problem solved. Hope it helps.