For the stock Traxxas 5729 flex shaft use Hot Racing SPN38P06 or SPN38SD06

Tekno RC NB48

This is the Extra Hard 18 Tooth 32 Pitch Blackened Finish Pinion Gear from Robinson Racing

2mm spacers

Installation is straightforward with basic hand tools during a normal chassis service

Traxxas 6780A Complete Center Differential Fits Hoss 4X4 VXL Mini 8IGHT Parts For the stock Traxxas 5729Traxxas 6780A Complete Center Differential Fits Hoss 4X4 VXL Restore smooth, balanced power delivery with this genuine Traxxas complete center differential for the Hoss 4X4 VXL. Supplied fully assembled, it lets you replace a worn or damaged center diff in a single step and get back to bashing fast. Built to Traxxas factory specifications for reliable performance, it installs as a direct replacement with standard hobby tools. Genuine Traxxas