Shimming freehubs

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mattsccm
Posts: 2875
Joined: 28 Nov 2009, 9:44pm

Shimming freehubs

Postby mattsccm » 17 Aug 2015, 9:47am

I have pile of Shimano ( and copies) freehubs, all of which have play and rattle.
Made the tool to pull them apart.
Just what will I find inside and what do I do with them?
I ask because I am usually very good at pulling things apart and then finding out that something I hadn't seen has moved or sprung off into the wide world.
Any tips Brucey?

Brucey
Posts: 36646
Joined: 4 Jan 2012, 6:25pm

Re: Shimming freehubs

Postby Brucey » 17 Aug 2015, 9:54am

the bit your tool fits (lets call it the top ring) unscrews on a left hand thread. Inside you will find all the same parts as in a screw-on freewheel, but writ a bit smaller; still 1/8" balls though. The top ring sits on a bed of shims, and if you are lucky it is simply a question of removing one or two shims. You can lift them using a pair of tiny screwdrivers (or tools made from squashed lengths of -ideally non-magnetic- old spoke), one each side.

I usually lap the top ring if there is play that I can't take out easily using shims.

Unless the mechanism is faulty or the balls need to be replaced, there is no need to do anything other than remove the top ring and as many shims as you need, using trial and error. If you do take the thing apart it is just like a freewheel, so practice on those if you want.

Note that on many freehubs if you lift all the shims, you can get into trouble, because the balls can drop into where the pawls sit. Normally there is one very thick shim at the bottom of the stack, so try to leave that one be, if you can do.

There are various tricks for removing and replacing the dust cap in the freehub body.

Note also that shimano freehubs use one shim type and many other freehubs use a slightly different shim design, so try not to mix them up, 'cause it'll be trouble if you do.

If there is a 'difficult to replace' freehub, I will regrind the bearing surfaces to make them perfect. If you don't do this a correctly adjusted (but worn/previously corroded) freehub can be a bit rumbly when freewheeling. The rumbling is 'mostly harmless' but a bit annoying; often it is louder than before, when the freehub was badly adjusted.

have fun!

cheers
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Cyckelgalen
Posts: 11
Joined: 21 Sep 2018, 11:29am

Re: Shimming freehubs

Postby Cyckelgalen » 10 Feb 2020, 8:57pm

Freehub body play.
Should there be any? How much is acceptable.

I have a new wheel,with a new M765A hub with very noticeable play with the axel removed/undone.
I can wiggle the free hub around at leat one mm. Is it normal having to remove shims on new higher end hubs?
Thanks

gregoryoftours
Posts: 1052
Joined: 22 May 2011, 7:14pm

Re: Shimming freehubs

Postby gregoryoftours » 10 Feb 2020, 11:48pm

Brucey wrote:There are various tricks for removing and replacing the dust cap in the freehub body.

Do you have any tips for reliably removing these? I can do it ok for some but it's by no means guaranteed, and it's hard to get the ones with a thin rubber skirt out without damage.

Brucey
Posts: 36646
Joined: 4 Jan 2012, 6:25pm

Re: Shimming freehubs

Postby Brucey » 11 Feb 2020, 7:34pm

Cyckelgalen wrote:Freehub body play.
Should there be any? How much is acceptable.

I have a new wheel,with a new M765A hub with very noticeable play with the axel removed/undone.
I can wiggle the free hub around at leat one mm. Is it normal having to remove shims on new higher end hubs?
Thanks


The 756A hub is branded XT but it is of lower quality than previous incarnations of XT, even the 756 model. I have very rarely encountered a new shimano hub (of any cost) which had zero free play in the freehub bearings. Note that if the freehub body moves around (because of bearing free play) then it will be costing you in terms of efficiency. However once correctly shimmed, they seem to last for ages without needing to be done again.

NB do check that the freehub body is not moving wholesale on its mountings; is the hollow bolt tight?

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

Brucey
Posts: 36646
Joined: 4 Jan 2012, 6:25pm

Re: Shimming freehubs

Postby Brucey » 11 Feb 2020, 7:40pm

gregoryoftours wrote:
Brucey wrote:There are various tricks for removing and replacing the dust cap in the freehub body.

Do you have any tips for reliably removing these? I can do it ok for some but it's by no means guaranteed, and it's hard to get the ones with a thin rubber skirt out without damage.


A trick that works well with almost any steel dustcap (rubber lip or not) is to use a suitable piece of tube (eg a socket) to drive the seal further into the hub. This will cause it to become slightly dished, at which point

a) the dustacap will loosen in its mounting and will come out easily and
b) the dustcap will need to be reshaped/reflared before it can be refitted securely.


hth

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

gregoryoftours
Posts: 1052
Joined: 22 May 2011, 7:14pm

Re: Shimming freehubs

Postby gregoryoftours » 17 Feb 2020, 8:16pm

Thanks, I'll give that a go when I next have to, I'd rather leave them in place unless necessary to remove them. I've pushed the seals back in with a socket before but never thought to start them off loose in that way too.

PT1029
Posts: 718
Joined: 16 Apr 2012, 9:20pm

Re: Shimming freehubs

Postby PT1029 » 17 Feb 2020, 8:26pm

re Brucey's comment
"NB do check that the freehub body is not moving wholesale on its mountings; is the hollow bolt tight?"

In my experience, if the hollow bolt (that clamps the freehub to the hub shell) is loose, there is play at the rim as though the wheel bearings are loose. The difference is, as you wobble the rim from side to side, the play at the hub is not at the cones, but between the freehub and the hub shell, this manifests itself as varying distance between the bottom sprocket and the spokes which is easy to see.
If you encounter it a few times, you may notice the play in the "hub" feels a bit different from secure freehub/loose cones play.

Brucey
Posts: 36646
Joined: 4 Jan 2012, 6:25pm

Re: Shimming freehubs

Postby Brucey » 17 Feb 2020, 8:40pm

gregoryoftours wrote:Thanks, I'll give that a go when I next have to, I'd rather leave them in place unless necessary to remove them. I've pushed the seals back in with a socket before but never thought to start them off loose in that way too.


For a long time, neither did I. But eventually I noticed what was happening; they say 'even a blind squirrel sometimes finds a nut'. I think what happened was that whilst refitting it, I drove a seal too far into the hub (not for the first time) and finally noticed that when I did this, the seal always became a slack fit and needed to be reflared. Then the penny finally dropped...

Re the hollow bolt being loose; in about half of the shimano freehubs I have serviced, the hollow bolt could easily be tightened another quarter turn. Most usually there was no sign that there was any looseness per se, just inadequate tightness.

In the event that freehub body has been moving around, and/or the bolt tightens half a turn or more, I suggest that it is best to remove the freehub body, and clean/inspect the interface. If there has been much movement, the debris by itself (leave alone any damage to the seating) may render the assembly unreliable. I'd also suggest checking the bolt again after a few hundred miles use.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~