79 T-18 4th gear popping out

[cj5 Overkill]

New to the forum. Ive had my jeep for a few years now and always had a problem with it not staying in 4th gear. While doing my LS swap, we rebuilt the T-18 with a master rebuild kit from novak. New snychros, bearings, even rebuilt the shift forks, new detents, balls, springs..etc. While on a drive last wknd doing my tune, it started popping out of 4th again. I pulled Transmission out and took it apart again. This time replacing the only gears I could find, 1st, 3rd and 4th. They were worn, but not terrible. Also doing a new Transmission mount and torque bracket. I just got the Transmission back in last night and should be able to drive it this wknd. The other thing I am doing is switching to straigt 50w oil in it and the Dana 20 . If this doesnt fix it, can anyone on here tell me what else I can possibly check? I have too much money in adapters, custom drive shafts...etc to replace the Transmission with something else. Any help is greatly appreciated.

 

[Torxhead]

I would suggest 80w-90 gear oil for the T-18 and Transfer Case . I have seen where the Transmission cover clearance hole will kick the tranny out of gear with the body moving around and tired motor mounts. Welcome to the forum.

 

[cj5 Overkill]

Thanks for the quick response. Motor mounts are new and the hole is large enough its not touching the Transmission at all.

 

[Lumpy Grits]

What holds the gear in place is called a 'drive-gear'. When they wear, this will let the gear 'walk' out.
Bet this happens when you lift off the fun-pedal.
LG