Any SM465 transmission experts here?

bobs409

bobs409

 
Administrator
Thought I'd ask here first. My 71 C20 has the 4 speed w/granny gear SM465 manual transmission. It's got a lot of miles on it so could surely use a rebuild but I'd rather not do a full rebuild right now as we are going into winter so if a smaller quick and easy repair (trans in truck) is available, I'd like to do that for now. Here's the situation:

On occasion, shifting from 2nd to 3rd is like hitting a brick wall, will not go into 3rd. This has happened about 4 times so far and of course, always while pulling out from a busy intersection! I tried to skip over 3rd and go to 4th just to keep moving but that let out a big nasty GRIND! :scared (that happened before too) After that I was able to go up into 3rd.

I'd guess it's probably some type of fork or slider that is worn somewhere. :dunno Rebuild kits are available and there seems to be some video's on doing that on line.

Just asking in case we have anyone that knows before I head out to google oblivion on a search... :read
 
bobs409

bobs409

 
Administrator
Well, spring has past but today I made an attempt. If you ever wondered if you could remove the top cover on an sm465 while still in the truck, the short answer is NO! My truck has the unboltable/removable floor hump but it's worthless! The transmission sits way further so can't do much of anything! Why have the access panel?????

So in short, I just wasted 1.5 hours of my time. :bang I'm thinking it might have a worn shifter fork but wanted to confirm before buying one. The heck with it. I'm too lazy to drop the trans. :D
 
benchseat4speed

benchseat4speed

Well Known Member
Supporting Member 7
Take rick up on his offer^^ Swap that 70k mile trans in, and dissect yours someday when you get time. I don't know why GM put the engine/trans so far forward on 67-72's. Pain in the butt. No such problems on a square body.

Denny is right, 465's have a 3rd gear jumpout problem too when they get some miles on em, maybe related to the problem you have. Solution is a spacer between 2nd and 3rd if I remember right, in lieu of snap rings. Might look into that further cause I don't remember for sure...
 
bobs409

bobs409

 
Administrator
benchseat4speed said:
Take rick up on his offer^^ Swap that 70k mile trans in, and dissect yours someday when you get time. I don't know why GM put the engine/trans so far forward on 67-72's. Pain in the butt. No such problems on a square body.

Denny is right, 465's have a 3rd gear jumpout problem too when they get some miles on em, maybe related to the problem you have. Solution is a spacer between 2nd and 3rd if I remember right, in lieu of snap rings. Might look into that further cause I don't remember for sure...
Click to expand...

Would have liked to get that unit but Rick no longer had it. My shifter doesn't jump out of gear but I have heard of that problem.

It's been behaving itself but only because I've been very careful with the 2-3 shift. A few times it got jammed up in that area which is the problem I'm having.
 
bobs409

bobs409

 
Administrator
My truck must be having PMS today or something. Twice it got jammed up. :bang

Decision; drop the transmission to fix it or cut the front of the floor hump so I can remove the top plate and fix in the truck. Hmmm....
 
bobs409

bobs409

 
Administrator
Jim Sullivan said:
Doesn't your truck have a removable center hup over the transmission Bob?
Click to expand...
Yep. Problem is the transmission sits too far forward. I attempted to remove the top shifter plate from the trans a few weeks ago but it doesn't clear the front of the floor opening. Had to put it all back together and re-group. :D What good is that removable cover, seems useless to me??
 
You must log in or register to reply here.
Top