I'm not a brake expert but over the years I've heard of similar problems being caused by the shoes being reversed. The smaller shoe is doing all of the work instead of the larger. I hope you get it figured out.
I'm with Tiny. Bendix brakes are a bigger pain in the keester than the old Huck brakes, mainly because if the shoes are in wrong, they don't work worth a darn.
The big ones are the primaries, and they should be in the aft posisition on each wheel.
