This is an interesting topic. I have the very same problem with my 1950 Chevy 1/2 ton.
The brakes build pressure on the back wheels and they eventually drag the motor down and then I notice I do not roll while in neutral on an incline.
I have heard these various causes from numerous people:
1) Bad flex hose.
2) Master cylinder adjustment rod not set right.
3) Weak return spring on brake pedal.
4) Weak or worn springs on brakes/shoes.
5) Bad wheel cylinder(s).
6) Bad brake line or obstruction in line.
7) Brake shoes/pads installed wrong place.
8) No relief pressure on master cylinder.
9) Brake line 'T' fitting is small opening on one side and larger on the other.
I too have been baffled by this problem. I have not heard of anyone on these forums fixing this problem, only heard of them checking into it.
If anyone knows how to fix this than make a new post and call it brake problems fixed.
(What do I do when this happens - just bleed off the line that is sticking, about every 15 miles!)
