[Prowbar]

A while back I rebuilt the SM420 transmission that I bought because the original transmission was pretty much shot.

The new transmission works great but, leaks some oil and has that annoying grinding noise that keeps chasing me.

I still had the original transmission in parts in the shed and figured I'd try to find out what causes this particular noise, having looked at all the other components in the driveline and pretty much ruled everything out except the transmission.

Taking a closer look at the transmission, it has to be something that is able to vibrate at a certain frequency. Everything is pretty much fixed except some parts in the shift cover, the reverse lever and the 2nd gear synchro ring.

My main suspect was the 2nd gear synchro ring. Taking a closer look, there is a step worn in the 2nd gear synchro lugs with corresponding marks on the gear, almost as it has been vibrating on the shaft. See photo.
The 2nd gear synchro is held in place by 2 wire springs riveted on the gear. See photo. When installed in the transmission, the springs grab the lugs only at the end and barely have any tension to hold it in place.

In other to prove my theory and repair the original transmission, I'd figured I'd see if I can rebuild it and fix the accompanying issues.