Saturday, February 20, 2010

Bicyle Freewheel Basics - Removal and Replacement

Bicycle Freewheel Basics

Practically every bike, trike or quad you will make will require some kind of freewheel in the transmission system. A freewheel is basically a sprocket attached to a ratchet, allowing the transmission to drive the wheel in only one direction - much like a socket wrench. Without a freewheel on a bicycle, you would have to pedal at all times, never able to coast. This type of drive system is called a "fixed drive" or "fixie", and is often used for strength training on an upright bicycle, where the rider works against the forward momentum in an attempt to slow or stop the vehicle. A similar fixed drive system would be found on a unicycle.

Since every trike, bike, and quad on this website requires a freewheel, let's explore the inner workings of the device and learn how to salvage them from old bicycle wheels in order to make repairs or adapt them to trike axles.

Some tools you will need
Figure 1 - Some tools you will need

Removal or repair of a freewheel requires only a few basic tools as shown in Figure 1. You will need two wrenches to remove the axle nuts, and the home made Shimano style freehub removal tool, which we will discuss soon. A center punch will also be needed if you plan to take the freehub apart to re-grease the bearings or repair the ratchet system. Cone wrenches and professional freehub removal tools are also available at many bike shops, but i can tell you from experience that the simple home brew freehub remover is much better than the professional tool and will last forever. I have broken 2 store bought freehub tools, but have never had any problems with the home made remover.

Cartridge freewheel and Shimano type
Figure 2 - Cartridge freewheel (left) and Shimano type (right)

Before going any further, make note that there are two distinct types of multi-speed freewheels and hubs; the cartridge type as shown in the left of Figure 2 and the classic Shimano type shown on the right of Figure 2. Only the Shimano type of freehub can be used for trike or quad axle mounting as it can be removed as a complete working unit by unthreading it from the hub as will be shown soon. The cartridge style freewheel cannot be removed from the hub (only the chain rings), as the ratchet system is built into the hub as an integral unit.

A Shimano freewheel is easily identifiable as it will have a recessed bearing race with two or more small holes in the ring that allow it to by removed. The cartridge steel freewheel will not have a visible bearing race, but instead a spline with several inner teeth. Cartridge style freewheels are usually found on more expensive wheels and aluminum hubs, whereas the Shimano style is usually used on lower quality department store bicycles, often having a steel hub.

More of this free plan: