Shimming freehubs

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mattsccm
Posts: 2888
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: 36822
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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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

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: 1060
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: 36822
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: 36822
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: 1060
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: 721
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: 36822
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~~~~~~~~~~~~~~~~~~~~~~~~

bgnukem
Posts: 252
Joined: 20 Dec 2010, 5:21pm

Re: Shimming freehubs

Postby bgnukem » 18 Feb 2020, 3:11pm

Going to have a go at this freehub adjusting malarkey.

Got myself a removal tool from somewhere online, and some 1/8" Grade 10 ball bearings.

Is it very difficult to stop the bearings falling out of position when opening up the freehub, and making them stay put when reassembling? How many balls per race in a typical Shimano freehub?

Do the pawls and springs fly apart when the freehub is opened?

Also I take it the thread is left handed when undoing the freehub body ball cup?

Sorry if this info is upthread but can't read at the mo as I'm at work.

Thx,

Ben

Brucey
Posts: 36822
Joined: 4 Jan 2012, 6:25pm

Re: Shimming freehubs

Postby Brucey » 18 Feb 2020, 5:37pm

its all upthread. If you are just reshimming then you remove the lockring/cup, the top layer of shims and nothing else.

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

bgnukem
Posts: 252
Joined: 20 Dec 2010, 5:21pm

Re: Shimming freehubs

Postby bgnukem » 19 Feb 2020, 5:57pm

I'd assumed I'd need to remove all the shims to replace both rows of bearings? Or is this more hassle than it's worth?

Incidentally I lubricate my freehubs with grease via the rear seal and they don't tend to wear out. However the most recent hub I've used (Shimano XT 780) seems to have a fixed seal such that it's not possible to get more than a few drops of oil past the seal into the freehub body. It's currently skipping despite a recent service and I think will have to come off and be immersed in oil to remove any water or muck. Progress??

Cheers,

Ben

Brucey
Posts: 36822
Joined: 4 Jan 2012, 6:25pm

Re: Shimming freehubs

Postby Brucey » 19 Feb 2020, 11:12pm

bgnukem wrote:I'd assumed I'd need to remove all the shims to replace both rows of bearings? Or is this more hassle than it's worth?

Incidentally I lubricate my freehubs with grease via the rear seal and they don't tend to wear out. However the most recent hub I've used (Shimano XT 780) seems to have a fixed seal such that it's not possible to get more than a few drops of oil past the seal into the freehub body. It's currently skipping despite a recent service and I think will have to come off and be immersed in oil to remove any water or muck. Progress??


it is pretty much a waste of time to replace the balls in a freehub; if they are corroded they are never the only thing corroded, so if you go to the trouble of fitting new balls the bearings will still be rumbly, just a bit less rumbly than they would be with the old balls in. If they are not corroded then they are best left as they are.

The very first thing you should do is whip the axle and 1/4" bearings out of the hub, and add lots of oil in the region of the RH hub bearing cup. Then, holding the freehub body in one hand, with the wheel vertical, spin the wheel clockwise on the freewheel bearing. After a few minutes the oil will have worked into the freewheel mechanism and you will know if the freehub body needs to be pulled apart or not. If the mechanism is very sticky to start with, use GT85 before the oil.

As I have already indicated when adjusting the freehub bearings, it is necessary to remove

a) the dust seal
b) the bearing cup/lockring/freehub cone
c) the uppermost (thin) shims only.

NB There is no need to remove the freehub body from the wheel, indeed it is entirely counterproductive; it just makes everything you do subsequently more difficult and/or more likely to go wrong. Provided the wheel is kept horizontal once the lockring is off there is no need to disturb anything else in a simple service/adjustment and if the freehub body is still working once oiled, there is little to be gained in most other circumstances too.

If you are daft enough to disturb the (much thicker) base shim, you will be greeted with the spectacle of the 1/8" balls falling down into the workings, and the most likely outcome is then that you will have to strip everything down to retrieve them. IME this at least doubles the length of time it takes to do the job, and it makes it almost impossible to avoid mixing the LH 1/8" balls with the RH 1/8" balls (bad).

If you want the freehub to work well for a long time, use a good SFG in the RH hub bearing; this will gradually mix with/replace the oil in the freehub body and it will keep everything sweet for the longest time with the least effort.

Once the freehub body is correctly adjusted and lubricated, maintenance then consists of simply adding more SFG to the RH hub bearing at intervals. Once year ought to be enough for most applications, and it is a five minute job; you just need to unscrew the LH cone about 5mm and then push the axle to the right; the gap is then big enough that SFG can be added to the hub bearings.

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

Brucey
Posts: 36822
Joined: 4 Jan 2012, 6:25pm

Re: Shimming freehubs

Postby Brucey » 19 Feb 2020, 11:31pm

BTW I have a big box of super quality 1/8" SKF ball bearings on hand but most of the 1/8" balls sold for bicycle use are not accurately made. Used balls in freehubs/freewheels, if they don't go rusty, tend to wear themselves so that (in the same bearing) they match one another more perfectly than they did when new. Even slightly rusty balls may be closer in size to one another than a new set of cheap ball bearings.

I think that inside freewheels, grade 25 or better balls are an unnecessary extravagance; I happened to have my super 1/8" balls for unrelated reasons and I certainly wouldn't have bothered to buy them just for freehub bodies.

So in order I prefer

a) to not dismantle the whole thing (it is usually a waste of time, one way or another)
b) to use the old balls again, being sure to keep the LH balls and RH balls separate from one another
c) to use cheap balls in a worn/corroded freehub body
d) to use posh balls in a freehub body.

If the flush with GT85/oil reveals a working set of pawls the main risk in not dismantling the thing is that the pawl spring might be corroded such that it may fail sooner rather than later. However IME this only ever applies if the freehub body is so corroded that when flushed, it is puking brown crud out like there is no tomorrow.

If c) applies then the chances are excellent that the freehub body will need adjusting again sooner rather than later, and that eventually it will 'settle down'. If it works for a few weeks (eg in non critical service) without problems then the chances are excellent that it will carry on working. If you are still leery of it, you can replace the spring/balls once there is a bit more wear on the bearing surfaces and the net result will be better than if you had done this to start with. If you know you might do this anyway, there is no real point in replacing the balls to start with.

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

bgnukem
Posts: 252
Joined: 20 Dec 2010, 5:21pm

Re: Shimming freehubs

Postby bgnukem » 20 Feb 2020, 11:47am

Thanks for the top tips!

I'll keep the freehub body on the hub. Think I'd rather experiment with a spare body fitted to one of my wheels first before I start on the usual one.

Got a bag of Grade 10 1/8" bearings from Simply Bearings yesterday so I might at least replace the outer set of balls without disturbing all of the shims.

The XT hub has the oversized aluminium alloy axle so not sure if my freehub cone removal tool will work with it, as compared with the usual 9mm steel axle hubs, but I'll certainly need to flush the body with oil I think. I just don't like the idea of oil leaching back out of the freehub bearings and contaminating the drive-side hub bearing grease.

Is there a decent semi-fluid grease (I'm assuming thinner than NLGI 2?) easily available? I've been looking for the Castrol SBX recommended elsewhere on here but it seems to be available from Australia only, or else in boxes of twelve grease gun cartridges costing around £135......