Classic/Antique Car Repair: 1941 vacuum shift, shift linkage, torque tube

Question
i have a customer with a 41 chevy with the vacuum shift. the problem is it won't stay in reverse. i have remove the vacuum srevo and cleaned up the metal cylinder and replaced all the rubber parts along with adjustment as per the service manual. i purchased the washer that is use for the adjustment. it will stay in reverse if you hold it or let the clutch out. 30 years of working on cars ,but none like this

Answer
These vacuum shifters worked real well when they worked and were a real pain in the sitter when they did not. However the problem that you are having does not really sound like a vacuum shifter problem directly. It almost sounds like a work shifter fork or a problem in the detent mechanism in the transmission. What could be happening is that the reverse idler or gear is not sliding into full mesh with its mates. As a result the vacuum shifter thinks that the driver is trying to get the unit out of reverse. This explains why it will stay in reverse when you let out the clutch as there is then pressure on the reverse gear, enough to keep it from sliding back to neutral. As this is a torque tube drive car it is a real pain to get the transmission out of the car but you might feel the defect by disconnecting the linkage from the transmission and shifting it by hand.  Also check the shift linkage pin holes to be sure that they are not worn and preventing you from getting a full throw on the shift. If the holes are worn they can be brazed in and re-drilled.