The ‘Zip-Rack’ is a fully assembled shaft and gear set that has been treated with our famous back-cut service. We start with a full set of new Andrews gears and shafts. The engagement dogs are carefully machined to the proper rake and depth by Zipper’s for positive engagement, eliminating missed shifts at high RPM. The gears and shafts are assembled with new thrust washers and bearings, then installed on a billet door. Big Twin models are assembled using our billet transmission door specially machined to include super-strong double-row ball bearings which minimize shaft flex while providing the best support and strength possible. Machined billet or black powder coat finish.