The stock inner bearing race was press-fit onto the transmission main shaft in all Big Twin models from 1985 through 2007. The inner primary bearing rides on this race. Engines producing 100+ HP force the stock inner bearing race to walk on the main shaft. If it walks inboard, it will damage the main drive gear seal and cause a transmission oil leak. If it walks outboard, it will cause a primary oil leak. The High Torque Bearing Kit eliminates these oil leaks and eases serviceability.