Popping out of gear

[Kenneth Cole]

Hi
I have an M37 that I put in a 318 poly still using the stock tranny. Driving along and if I back off on the gas she will pop out of gear. This will happen for both third and fourth gear. If I keep a little pressure on the shifter it will stay in.
Any thoughts.
Thanks for the help.
Ken

[Gordon Maney]

A most likely, contributing cause is a badly worn pilot bushing. That is the bushing that supports the forward end of the transmission's input shaft in a machined bore at the rear end of the engine's crankshaft.

Having said that, I would want to have a look inside, too, meaning disassemble the transmission and evaluate the front and rear case bearings and the needle bearing set between the input and output shafts. Some or all of those bearings could be worn, also.

There is also a detent ball and spring assembly associated with the 3rd/4th shift rail that needs to be working properly.