Help, I'm really in a pickle. I have a 1990 Pace Arrow on a Chevy P-30 chassis. I can not get the parking brake to function. Replaced power steering pump, front calipers and flushed system with new fluid. I get pressure from the spool valve but no pressure to parking brake. Every mechanic I talk to says never seen a system like this. What is the mecanism that applies pressure to the brake drum on the drive shaft. Where can I go to find parts for this system. Local truck dealer has no clue.