Bicycles require periodic maintenance and cleaning to keep them operating at peak efficiency. As part of that maintenance, riders must remove the cogs on the rear wheel that allow the bike to change gears. Shimano manufactures cog cassettes that make removal and reattachment relatively simple, also allowing riders to replace worn cassettes or single-speed cogs with ease. Removing the cassette requires use of a couple of special tools as well as one found in most toolboxes.
Freehub vs. Freewheel
Freewheel systems nearly monopolised the rear-hub market into the 1980s, when the Shimano freehub cassette system began gaining popularity, according to renowned bicycle mechanic Sheldon Brown. The main difference between the freehub system and the freewheel one is the way they connect. The freewheel system has threads, so the cogs screw into place, while the freehub system uses grooves and spines to hold the cogs where they belong.
The freewheel system allows more interchangeability, meaning cogs from different manufacturers work on nearly any bike. Although the Shimano freehub system is manufacturer-specific and riders cannot slide cogs from different brands onto the hub, it offers benefits such as a reduced chance of a bent rear axle and the ability to change the cogs without changing the ratchet mechanism.
Cassette Removal Tools
Removing the Shimano cassette requires tools commonly found in bike repair shops and on websites such as eBay. Riders need a lockring tool and a chain whip to do the job, and in some cases, they need an adjustable crescent wrench.
Some lockring tools include handles, negating the need for a separate wrench. When required, a large wrench is needed to fit over the relatively wide lockring. Riders should buy lockring tools designed to work with Shimano cassettes. The different slot-and-groove patterns from various manufacturers means a lockring made for another brand does not usually work with the Shimano brand.
Cassette Removal Process
Removing the cassette is a fairly quick process. First, remove the rear wheel from the bicycle to safely access the cassette. Then unscrew the quick-release nut, if necessary. To remove the lockring, press the lockring tool into the centre of the cassette, lining up the slots and grooves. Holding the cassette still requires wrapping the links of the chain whip around a cog, usually one in the middle of the cassette, and gripping the chain whip's bar tightly to prevent movement. For lockring tools without handles, adjust the wrench so that it fits snugly around the lockring tool before turning it counterclockwise to loosen the lockring.
It only takes a few turns to loosen the lockring, which can then be removed. To take off the Shimano cassette, pull it straight off the hub as a single unit. Some cassettes have rivets or pins holding them together as a unit, but others have a several cogs attached together while leaving most of the cogs and spacers as single pieces. Lay out the single pieces in order when separating them for cleaning. This helps ensure they go back onto the hub in the correct order.
How to Buy Shimano Cassettes on eBay
To find the largest selection of Shimano cogs on eBay, type 'Shimano cassettes' in the search field found on any eBay page. Narrowing the search helps you find exactly what you need. For example, you might search for 'Shimano 10-speed cassette', substituting 7-speed or 9-speed as needed. You can also search by bike type, such as 'road bike Shimano cassette' or 'Shimano cassette for mountain bike'. Searching for 'Shimano cogs' or 'Shimano sprockets' also yields helpful results. Sellers on eBay offer the necessary tools, including chain whips and lockring tools, as well.