Air bag pump is running, new airbags . rear bags wont air up.

I can only assume you're talking about the ill-fated suspension of a late 90s/early 00's Lincoln Navigator. These trucks are famous for having air suspensions that just don't last. If it were me I would go ahead and just switch over to coil suspension. You can do it in your own driveway and it will last you the rest of your car's life without any issue since it's a simple mechanical part rather than a complex web of electronic/pneumatic parts. Check out what Lincoln products these guys have You searched for lincoln navigator Strutmasters

I'm assuming you have a 4x4. Anyway, I would check the little 1 inch long, black line union over by the brake master cylinder. This "union" connects 2 air lines together. If it splits down the middle, all the air will vent out instead of in the air bags. Your welcome to use this Ford Expedition air suspension diagnosis & repair section 1997 2002 Ford Expedition Air Suspension Diagnosis Repair

These Lincoln air suspensions are terrible. I have converted many over to coil springs at a fraction of the cost of replacing/repairing the bags. If the rear bags don't inflate, there is a broken air line to the bags or the bags are leaking