BTwin hub replacement

[johnn]

Hi, I've just replaced the cassette and chain on my daughter's Btwin Alur 700 but find the cassette (and the freehub once the cassette is removed) rocks on the axle, as if whatever bearing(s) the freehub contains are worn. The wheel bearings themselves feel smooth with no discernible play... no obvious cones/nuts, so I suppose they are sealed bearings.
Looking to replace the freehub, but I can find no way to remove it - no hex aperture inside the axle against which the body could perhaps be unscrewed, no ring nut...
Replacing the whole wheel seems very inefficient, so any advice on doing this job gratefully received!
https://www.flickr.com/photos/200145077 ... h4075a7705
https://www.flickr.com/photos/200145077 ... 35914v0929

[slowster]

I can find no way to remove it - no hex aperture inside the axle against which the body could perhaps be unscrewed

Have you checked from the non-drive side of the hub?

It looks like many of the freehubs on Decathlon bikes have a bolt which is accessed from the non-drive side, e.g. see the various photographs in the links below showing the bolt and female thread etc.

https://www.decathlon.co.uk/p/9-10-s-ca ... mc=8292680

https://www.decathlon.co.uk/p/cassette- ... mc=8756153

https://www.decathlon.co.uk/p/9-to-10-s ... mc=8758041

[rjb]

Reshimming the freehub may reduce the play. Can be done without removing the freehub from the hub.
Search on the forum. Brucey posted a thread on how to do it.
Here's one for starters. viewtopic.php?t=144203

[Brucey]

if the freehub body fastener is accessed from the NDS there is no way of telling if you are looking at some kind of nut or if is a bolt. There is also no way to tell if it is a LH or RH thread. Fortunately you can re-shim the freehub body in situ, provided you can deal with the seal and the (LH threaded) cup underneath it. This is usually successful, although it does require a special tool.

[slowster]

Decathlon list one other freehub body, which just pulls out of the hub shell - https://www.decathlon.co.uk/p/shimano-a ... mc=8530770. Your freehub has a similar appearance/colour. There's a product number visible on the freehub body in one of the photographs, which you might be able to check against one on your freehub.

[TheBomber]

Are there any symptoms? Eg is it noisy when ridden, the shifting is poor and cannot be corrected by the usual means etc? I ask as I've seen cassettes wobble so much it’s clearly visible to the rider behind, but they’ve not caused a problem. These days I’d fix it as I know how (re-shimming a cassette requires dismantling a part that Shimano describes as unserviceable), but you may be able to just live with it.

[Brucey]

IME freehub bodies can have very slack bearings and not manifest many outward signs of distress. However they seem to wear a lot more quickly when the bearings are already a bit slack. Note that this bearing (unlike all of the others on a bike) sees load or motion, not both at the same time. But only when properly adjusted; I think they can move under load when not correctly adjusted, hence the increased wear rate.

[TheBomber]

So, adjust to take up the slack if possible but wholesale replacement would be premature unless there are other troublesome symptoms. Mind you, it would bother me other than on a hack bike.

[johnn]

Wow! Firstly, thanks so much for such a great response to a newbie. Appreciated.

Now I may be missing something, but I haven't really got a solution that I know how to implement...

- Yes, I've tried from the NDS. On that side there is a bush threaded into the axle with a central aperture for the QR, I can easily remove that but then exploring the resulting hole with a thin rod gives the strong impression that there is nothing in there which might take a large allen key (I've seen that on other freehubs) or similar - all the internal surfaces appear to be smooth and concentric with the axle. I have tried to feel for either a nut or a bolt (the latter of course would have to be hollow) but I can feel a smooth surface all the way from the DS hole for the QR right back to the NDS exit: no flats and no thread.
- If I understand correctly, the 'reshimming' approach would require removal of the seal/retaining ring (?) that sits between the splined casing and the axle, viewed from the drive side. I can't see how to do that, and I'm afraid I couldn't see Brucey's explanation, not sure where (or how) I'd put a shim without taking the body off.
- The hub that just pulls off is interesting, and perhaps I'll find an innovative way of grasping and tugging this one (manual pulling hasn't worked yet). The splined hub is rocking relative to the axle within it, so if this is the way forward then the freehub probably has to have two elements with the rocking happening between them... otherwise it seems unlikely that the inboard end of the freehub could be so well stuck in the wheel yet I can easily wobble the outboard end (?).

(The eagle-eyed may have noticed in one of the pics that there could be a thin wire/spring just inside the outer shell of the freehub, running around the circumference, with a gap (at top left in the pic) perhaps so it can be removed to give the desired access. I'm afraid that's an illusion, I have since blown away the specs of dirt causing the illusion . )

Interestingly (perhaps) in one of the pics small notches can be seen at intervals along each spline, apparently spaced at the same pitch as the cassette sprockets. I've not seen such marks before, and can only guess that they are caused by those sprockets in some way. As far as I know the (old) cassette was never loose on the freehub (although the freehub was itself loose on the axle), so perhaps these marks reflect varying forces between the cassette elements and the freehub as the latter wobbles.

TheBomber, your comments resonate with me (although I don't think I have a way of taking up any slack). Having the sprockets wobbling can't help derailleur set-up but perhaps I'll just have to go for it...

If there are any more ideas or help it would be great. But whatever, thanks so much again for your efforts!

[johnn]

EDIT: And I'm afraid there is no number on the splines... just "11 SPEED", which is in fact countered with a "8/9 SPEED" shim inserted at the inboard end of the splines.

[TheBomber]

With the NDS parts removed as illustrated, does the whole axle tap out? Probably with the freehub body (FHB) still attached.

If the freehub is the design that just pulls off you could reinstall some of the old cassette so that you have a face (the inside of a cassette sprocket) that can be tapped from the NDS of the wheel. I can’t see this working with that remaining lock nut in place though.

Re the witness marks on the freehub body splines - they are common and don’t look deep. They can be minimised, but not eliminated, by tightening the cassette to the correct torque.

We’ve led you astray with talk of re-shimming - that relates to Shimano design FHBs. Yours would probably need the FHB bearings replaced. Getting the old ones out will no doubt be a challenge as IME they’re held in place by snap rings. Kind of like circlips but without the holes in them that allow removal. Because it was never intended that they would ever be removed.

[johnn]

Thanks Bomber. Hmm, it sounds like I'm basically barking up the wrong tree for this particular wheel... at the start it hadn't crossed my mind that it might not be intended to be replaceable.
So the wise decision seems to be to put it all back together, get the derailleurs set as best I can with the current movement in the cassette and see how it rides. If there are significant issues then it looks like a new wheel, either a direct replacement or something else.
Thanks again all for the really helpful advice .

[cycleruk]

In one of your photo's there is a locknut still in place. Have you removed this? Or is it on the axle?
https://www.flickr.com/photos/200145077 ... 5914v0929/

[Brucey]

i've just taken a hard look at your photo and I think you have 'the other kind' of freehub there; this kind has four cartridge bearings on the axle;,two for the hub, two for the freehub body. The freehub body on these is often Al (does a magnet stick to it?) in which case 'bite marks' seem to be par for the course. It often seems tempting to tighten the cassette lockring a bit more, but if you do you risk the end of the freehub body breaking off. I suspect that the best thing you can do (cassette-wise) is to remove most of the serrations from the cassette lockring and then retighten it.

When this kind of hub is worn it is usually possible to replace or rebuild the cartridge bearings; usually it is fairy obvious if you have this kind of freehub, because as soon as the axle is removed, the freehub body falls off.