OT . Gm 1 ton 4 speed problems

[Anonymous-0]

Need to pick some brains here . Have 79 chevy 1 ton in shop . 4 speed , granny low. Customer says it pops of of 2nd gear going down the road.I could not get it to do it for me,,but he swears it does. Could not pin him down if it was on accel , or coast. I pulled top of trans off, shift forks look okay . The brass rings appear to be okay . Never has any grinding going into gear, just jumps out. I can move the collar all the way engauged okay . Any ideas ? I don't get into much trans work .
Thanks
Bryan

 

[Anonymous-0]

I have a 78 chev 3/4 ton converted to 1 ton that jumped out of 2nd. It started out doing it once in a while then would not stay in 2nd at all. There was just slight wear on shifting fork. Replaced it and have not had any more problem.

 

[JDemaris]

Most likely, the dogs are worn out on 2nd gear. 2nd gear in the SM465 (117 mm RPO M20) trans is not a sliding gear -it's stationary. Engagement is done by the shift collar locking on to the little steel spurs on the end of the gear. Once they get worn - usually at an angle - they push them selves out of the shift collar. 2nd gear usually gets the most wear in any 4 speed.

If you look closely at them, and they are worn, you can assume the part of the shift-collar that slides over them when using 2nd gear - is just as worn.

As already mentioned, other things can cause it also - but dog/spur wear is common in 2nd gear.

 

[Allan in NE]

Oh Yeah,

Everything looks and operates just as it should and ya can't see a blessed thing wrong with it.

Nothing looks that bad for wear. Can't understand what this silly customer is talking about/can't make it do it. Everything seems just fine. What the heck is he talking about anyway?

Right?

Go further; tear the transmission completely out of the truck and take it clear down/disassemble to parade rest on your work bench.

That box has a nasty habit of wobblin' out those big carbonized, graphite-type bushings.

Will show up as a shifting, jumping out of gear and/or noise problem and is the most common root-fault with this transmission.

Allan