[Healeys] PBR servo

[healeymanjim at hansencc.net]

a while back i rebuilt a PBR servo with parts we got from down under.  it works but doesn't.  when you press the pedal, the servo appears to work OK, but then the pedal rides back up and the servo drops out and you need to push hard to stop.  i thought it would work out after a while, but now i need to go back into it an make it right.  i suspect the air valve, but does anybody have any ideas.  it is simple system, and seems pretty rugged, but something appears to be sticking.  a beer to the winning contestant. hjim