Old Britts – Commando Gearbox: How Does It Work?
Download the complete PDF version using the green download button at the top right of this page for an Old Britts technical article explaining how the Norton Commando four-speed gearbox works. Written by Fred Eaton, this illustrated reference breaks down the internal gear layout, the main shaft and lay shaft arrangement, the gearshift mechanism and the way power is transmitted through the gearbox in each selected gear.
The article begins with the basic gearbox structure, identifying the four gear pairs, their tooth counts, which gears are splined to their shafts and which run freely on bushings. It also lists the Commando gearbox ratios for first through fourth gear, then explains how movement at the shift lever acts through the gearshift pawl, ratchet plate, knuckle pin roller, quadrant, cam plate and selector forks to change the internal gear engagement.
Later sections show the gearbox in first gear, neutral, second, third and fourth, with photographs and clear descriptions of which gears are dogged together in each position. The cam plate section is especially useful for understanding the five indexing notches for the four gears and neutral, including why the neutral notch is smaller and why finding neutral can sometimes be more difficult.
Contents Include
- Norton Commando four-speed gearbox operating principles
- Main shaft and lay shaft gear arrangement
- Gear tooth counts and internal gearbox ratios
- Splined gears versus free-running bushed gears
- Gearshift pawl, ratchet plate and quadrant operation
- Cam plate and selector fork movement
- Neutral index notch explanation
- First gear power transmission path
- Second and third gear engagement details
- Direct fourth gear operation
- Photographic views of gearbox internals in each gear position
