Transmission slipping out of 3rd

[Randalla]

I have a 67 1/2 roadster with a 5-speed transmission. The transmission shifts through the gears fine with no noise and everything seems to be working well except when the car is in third gear it slips into neutral when decelerating quickly. If the car is under load it stays in third. I've now resorted to holding the shift lever forward when in third gear to keep it there. This obviously is a pain the backside. There does not seem to be any interference with the tunnel causing the issue. Have any of you had a similar issue or know what may be causing this condition? Thanks

[redroadster]

Replace the speed gear, syncro sleeve , check the detent balls on the shift rod, is the usual prescription.
They have 90 degree flat rub areas,that can get tapered .

[Randalla]

Arghhhh. Sounds like I'll need to pull the engine and transmission and have it gone through. Was hoping for an easy solution, though my gut told me I'd have to pull it out. Thanks.

[david premo]

It’s most likely the bearing under the gear on the output shaft. It’s also possible that it’s the pocket bearing between the input and output shaft.