A Shimano freehub is the mechanism that holds a bicycle's rear sprockets onto the axle. It is a relatively modern invention. With older hubs, the sprockets screwed onto a threaded hub. The sprockets, however, glide onto a freehub along a set of grooves called splines. A lock ring then threads onto the hub to hold the sprockets in place. To replace the freehub, you need to remove the sprocket set, or cassette, as well as the axle and bearings.
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Things you need
- Lock-ring tool
- Chain whip
- 10mm Allen wrench
- 15mm cone wrench
- 17mm open-end wrench
- Waterproof grease
Remove the rear wheel. According to BicycleTutor.com, unhook the cable or deflate the tire to release the rear brake. Then make sure the chain is on the smallest sprocket by adjusting the rear shifter. Loosen the quick-release lever and take off the wheel. Lay the wheel sprocket-side up on your work area.
Slide the lock-ring tool onto the splines of the freehub. Some lock-ring tools have a long handle that mechanics can turn. Others are hexagonal and can be moved with a wrench, whose size may depend on the lock ring you're using. The lock-ring tool loosens counterclockwise. This will engage the freewheel, however, meaning that the whole cassette will spin freely as you turn the lock ring. To turn the lock ring independently, hold the sprockets in place with a chain whip, which grips the sprockets when you lock its chain into their teeth.
Remove the axle. The hub is on the drive side, the side that held the sprockets, but the axle is secured on the opposite side, where a cone and locknut hold the axle in place. Turn the wheel over to work on it. The cone is a tapered section of metal beneath the locknut, and at the top of it are two flat edges for a wrench to fit against. Hold the cone wrench against the cone flats and use the open-end wrench to unscrew the locknut on the end. Remove the cone and locknut, then pull out the axle through the driver's side.
Remove the freehub. Unscrew the bolt holding the freehub in place using the Allen wrench. Then you can gently slide your new freehub into place. Regrease the end of the bolt before screwing it back in.
Tips and warnings
- Replacing your freehub is a great opportunity to clean or replace your bearings. Rarely do you have such easy access to them.
- Also, be sure to clean each part and use fresh grease as you put the rear assembly back together.
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