860 jumps out of 3rd gear

[cdv]

well i replaced the spring and plunger old one was not that bad,, but i think the 3rd gear slide rail may be worn do you think i can drill it a little deeper or not ,, all the gears in it look real good and jumps out of gear with no load when i move the tractor 10 feet or so
 

[Texas!]

I'll bet that your 3rd-Rev sliding coupler is worn out. Complete trans disassembly to replace it. Don't ask how I know.
 

[Dean]

If it jumps out or gear as you describe under load (not coasting), the gear selector is not fully engaging the teeth on the sliding collar and/or the collar teeth and engaging teeth on the meshing gear(s) is/are badly worn.

You cannot visually inspect by looking at the gear teeth in a constant mesh transmission.

Dean
 

[cdv]

Dean. It jumps out when it is coasting I looked at the gears when I had the top off on change the oil I didn"t see any thing wrong with the cupler thanks carman
 

[Dean]

Not uncommon to jump out when coasting when engaging teeth are worn.

If it jumps out under load as well the teeth are most likely worn well beyond service life.

You may also want to check for a loose, bent or badly worn shifting fork.

Dean
 

[Texas!]

Here's what worn sliding coupler teeth look like. Believe it or not, all of the torque from the input shaft into the transmission is transferred to the output shaft through about 1/8" engagement between the coupler teeth and the gear teeth. You can weld up the notch in the shift rail and re-cut it about .100" further out so that you gain another .100" of tooth engagement. Thanks to Zane for that mod.

 

[GlenIdaho]

My 850 does the same and I am preparing to split the tractor for repair. Check out the thread below, Zane and Tony Jacobs address this issue. I plan to follow their advice.
3rd gear repair