M90 Gearbox Reinforcement Welding

The problem with the M90 box is that with careless gear shifting, the 3rd gear synchro ring can break and fragments will destroy the entire box. Reinforcement welding locks the synchro ring in place.

Welding is done with MIG, not TIG. The reason is that TIG welding would produce significantly higher heat stress, and the bearing surfaces nearby could be damaged. The part should not be cooled immediately after welding — this causes shrinkage and the shaft may warp.