This book gives an engineering overview of the 1931-1936 reverse and 1936 4-speed transmissions used on the Harley-Davidson VL Big Twin flathead motorcycle. The 1936 gearbox was the first constant mesh 4-speed for a Harley Big Twin, pre dating the similar and long lived Knucklehead box by a few months. Overhaul procedures are then given for the two geearboxes, with complete parts lists and prices from the 1939 parts book and the present day. It is concluded that the maket value of the reverse transmissions does not yet reflect the cost of a good restoration, while the demand for the 4-speed is such that the present day reproduction of spare parts can be justified.