sm420 transmission problem

[63cory]

i have an old sm420 transmission in my 1963 chevy truck and it popping out of 2nd gear i removed the top cover and the all syncros and gear blocks are in good condition i dont know whats wrong any body have any ideas.

[padresag]

how much metal in the gear oil when you drain it? It is more than likely just the bearings and the syncros wearing down. replace the bearings and while you are doing that replace the synro rings and it will be just about like new
ron

[63cory]

The fluids were clean no metal shaving all the bearing and syncros only have around 10,000 miles miles on them i was looking at it and the syncros are loose they move back and forth a little is there any ajustment

[Roadmaster]

I bought a 'rebuilt' SM420 from a friend and it jumps out of second geat as well. (counting granny low as first)

[padresag]

Originally Posted by Roadmaster

I bought a 'rebuilt' SM420 from a friend and it jumps out of second geat as well. (counting granny low as first)

you guys may just have excessive end play in the shafts from worn thrust washers, then again some rebuilds are just a fluid change and a oil change.
new bearing usually solve a lot of the problems for these guys, but those washers wear out to.
shifter forks also wear
ron

[ky-donzi]

Check the Detent springs on the shift rail. If there is no pressure on the Detent balls that would cause it also
Posted via Mobile Device