There’s nothing like a constant cycle of getting your bike filthy and then cleaning it in a hurried fashion to show up any component deficiencies. And during the winter months several bits of bike are likely to give up the ghost. One of the most common fatalities is the humble freehub body. And without that working, you’re going nowhere.
There are two main failure modes. Either the freehub will stick so that it doesn’t freewheel, leading to the chain tangling up every time you stop pedalling, or it’ll stick so that it freewheels both ways with the obvious detriment to power transmission. What you do about it varies according to your hub. Hope and some other high-end hubs have freehubs that can be dismantled, cleaned out, relubed and rebuilt. Regular Shimano freehubs can, in theory, be stripped down like this but in practice it’s a lot easier just to replace them. You only have to replace the actual freehub mechanism, not the whole hub, and it’s a pretty straightforward job.
This is one of those jobs for which cleaning your bike is a must. This is a uniquely grimy bit of the bike…
1. This job’s spannertastic. You’ll need a big adjustable spanner to drive the cassette lockring tool, a chainwhip, a 10mm Allen key and a selection of cone spanners (15 and 17mm for Shimano hubs), plus some grease.
2. First job is to remove the back wheel and take the cassette off. Refer to our previous articles on those topics if you don’t know how. And marvel at all the gunk that accumulates behind the cassette sprockets. Mmmmm.
3. Next you need to take the axle out of the hub. You’ll need to gain access to the cones, which (depending on your hub) may mean removing a rubber seal. Carefully lift an edge with a small screwdriver and lift the seal off, pausing only briefly to admire the corrosion on your disc rotors.
4. This is where the fun starts. Choose a pair of suitable cone spanners and place on on the cone (the inner flats) and one on the locknut (the obvious hexagonal thing on the end of the axle) on the non-drive side. Arrange the two spanners so that you can pull them together with one hand to crack off the locknut. It may be a bit reluctant – you can try putting another spanner on the opposite locknut and undoing them that way.
5. With the locknut loosened, unscrew it completely from the axle, lift off any washers you may find beneath and then unscrew the hub cone itself. Lay all the bits out in the order they came off so you know which order to put them back in.
6. Now pull the axle out from the other end of the hub. Remove it slowly in case all the bearings fall out. With any luck things’ll be in good enough shape that the grease will keep them in place. Chances are, though, that your axle will look no more pleasant than this one in which case the hub bearings will make a bid for freedom. Like Pokemon, you’ve gotta catch ’em all or it’s a trip to the bike shop. Although if once you’ve cleaned them they’re anything other than smooth and shiny you might as well replace them anyway.
7. The freehub body itself is held on to the end of the hub shell with a hollow Allen bolt that the axle passes through. To undo it, get a 10mm Allen key, put it into the end of the freehub and turn anticlockwise. If your hub’s never been apart this may take a bit of heft.
8. With the bolt out, the freehub body should just slide off the splines that transmit the torque from the sprockets to the hub shell. At this point it may be possible to rescue a fading freehub with copious injections of 3-in-1 between the inner and outer parts at the back, but it’s at best a temporary fix – your best bet is to chuck it and get a new one, which has the added bonus of replacing the drive-side bearing surfaces.
9. Your new freehub body just slides on to the splines. You might as well put a dab of grease on the splines to ward off any possible creaking problems. Apply a bit of grease to the threads of the hollow bolt and do it up tight. There’s a recommended torque setting for it, but we haven’t got a torque wrench so we’ve never got around to finding out what it is. Then squirt new grease into the bearing surfaces (you’ll need to clean out the non-drive side ones first) and pop the bearings back in. A Shimano rear hub should have nine each side.
10. Clean up the axle, squirt some grease onto the cones and reassemble, making sure all the bits go on in the right order. Finally there’s the tricky bit – adjusting the bearings correctly. You need to fractionally overtighten the cone (so the axle rotates a tiny bit roughly) so that you can wind the locknut on and then back the cone off against it to lock everything in place. Once backed off the axle should rotate smoothly without rattling. If it’s still rough, it’s too tight. If the axle moves in any direction other than around more than a tiny tiny bit, it’s too loose. It’ll probably take a few tries to get it right. Once you have, put any rubber seals back on, replace the cassette, put the wheel back in the bike and go have a cup of tea…
There’s hundreds of top maintenance tips in the BM archive.