SM465 trouble going into gear

[2 Sweet]

Lately I’ve been having an issue trying to get my truck to go into gear after a cold start. ’89 K1500, 350, 4-speed manual w/ granny low. It acts like 1st gear is locked out. Pumping the clutch a few times in neutral and trying 1st again doesn’t work. It doesn’t want to go into 2nd either, and will grind bad if I try to go into reverse. I haven’t tried going into LOW but imagine it probably wouldn’t work either. It will usually go into 3rd with a little extra effort, then I can slip the clutch a bit to get the truck rolling, and at that point I can usually get it into 1st. Then it goes through the rest of the gears fine and shifts flawlessly the rest of the drive in all gears.


I drained the fluid from the trans and replaced with fresh 80W-90, made sure it was full, and it made no difference. It only does it after a cold start, and I don’t understand how it suddenly shifts perfect once I get going. It has never once popped out of gear or made any grinding noises or any other signs of failure. So what the hell is going on with this thing? It doesn't seem like it would be a clutch/hydraulic issue, but I really have no idea. I’m stumped.

 

[RichLo]

What type of fluid did you put in it? Amsoil Syncromesh is my go-to for most manual transmissions now.

 

[2 Sweet]

I just used 80W-90 gear oil, that's what everyone recommends for the SM465 and it looks/smells like that's what was already in it when I drained it

 

[2 Sweet]

You know what's weird? The truck hasn't had this issue at all since the day I posted this thread. Not even once! It's back to shifting flawlessly again. Goes into gear easily every morning after it sits overnight. I don't understand it, but I guess I don't need to worry about it any more.