M-37 1951 Transmission

[berhot]

I was having trouble shifting into 3rd and 4th. I though it was the snap-ring problem, but with the trans on the bench, top and side covers off; there is no metal in the trans. What should I check out next? Should I take the mainshaft out and check all the parts Thanks for you help.

[Charles Talbert]

The snap ring issue

The first noticable signs of the snap ring issue is trouble shifting into 3rd and or jumping out of 3rd gear. You can't see the snap ring until you pull the mainshaft out, then you can see what is going on with that. It is very typical to find the ring out of the groove or the groove broken off the end of the shaft or both. It is also typical to have lateral movement of 3rd gear on the shaft that you can check and see right now by sliding the gear back and forth on the shaft. If it will slide on the shaft more than a few thousandths, it's a high likelyhood the snap ring issue is in play.

This issue is most often associated with the early style transmission used in M37 trucks prior to the B1 series; however it does show up sometimes in the NP420 trans in the B1 trucks. In fact the last 2 420's I've built had the groove broken off the shaft.

[DAPM37]

interesting

so how do you fix those with the broken shaft?

[Gordon Maney]

so how do you fix those with the broken shaft?

Replace the shaft.