[TR] OD Transmission and Reverse Gear

[Randall]

If you can hear the clack from the solenoid (as opposed to the much softer click from the relay), then it pretty much can't be an
electrical problem.  A tiny chance it might be solenoid adjustment, but IMO a sticking clutch is much more likely.  (Usually when
the solenoid adjustment is right on the edge, it won't engage reliably but still disengages.)

Another possibility is a partially plugged relief port in the valve stem (red arrow in this photo 
http://s258.photobucket.com/user/TR3driver/media/A-type%20OD/A-TYPEODOPERATINGVALVEANDDRAINHOLE.jpg.html

But I'd suggest you call John and ask him about it before doing anything to the unit (including readjusting the solenoid).

PS, I believe thumping the brake ring (the black ring visible between the main OD housing and the tail housing) with a hide hammer
is the recommended cure for a stuck clutch.  It should stop sticking after a few cycles.

-- Randall