Shimano Freehub Service

[Jim77]

Hi all,

I am in the process of servicing the rear hub on my MTB (replacing the loose ball bearing in the cup and cone).

I wondered if it was necessary to service the Shimano free hub as well?

If so are there any good guides on how to do so?

Thanks

Jim

[slowster]

See viewtopic.php?p=1564606#p1564606.

[Jim77]

Thanks - I will read through carefully.

[cycleruk]

YouTube video :_
https://www.youtube.com/watch?v=X9gIEG1db0s

If you have a go then try not to damage the dust cap.
I have had a go at dismantling a freehub but could not get the inner cone undone.
(was not sure which way turn the cone - hadn't seen the video then)

[Jim77]

YouTube video :_
https://www.youtube.com/watch?v=X9gIEG1db0s

If you have a go then try not to damage the dust cap.
I have had a go at dismantling a freehub but could not get the inner cone undone.
(was not sure which way turn the cone - hadn't seen the video then)

Thanks will have a look.

[Jim77]

So from what I can make out Shimano does not recommend dismantling their freehubs for maintenance?!

[cycleruk]

Freehubs can get water in. I have seen one frozen on an MTB winters ride.
(pawls frozen open.)
Obviously would start working once thawed out but a service would really be needed.

[gregoryoftours]

Service is pretty fiddly, involving lots of tiny ball bearings (1/8") needing to stick in place while you re-assemble. Unless it feels like it actually needs it I would not open it up.

You could always remove it from the hub, (usually a 10mm Allen key anti clockwise from the front for a standard qr Shimano), take the seal at the back out and flush it through/re-lube suitably (can make it quite gritty for a while). Don't use lube that can gunk up if you're sending it through as far as the pawls, as it can interfere with the pawls' engagement with the ratchet and slipping/internal damage can result.

If you do want to open it up you can get a slotted tool to fit the cup race for cheap from Ali Express, or for a bit more from eBay. Shimano stopped selling their own tool years ago. You can remove shims from under the cup race if you have excessive movement/play in the freehub body. It's best to dismantle it still mounted on the hub.

[rareposter]

I wondered if it was necessary to service the Shimano free hub as well?

Sometimes flushing it with solvent, completely drying it and lubing with oil (rather than grease) can work but basically, if the bearings are worn, the freehub needs to be binned and replaced. It is ultimately a consumable part - one that typically lasts a very long time but the whole point of it being removable is that it can be taken off and replaced.

There's really very little that a home mechanic can do with it (and to be fair, there's very little that ever needs doing to a freehub anyway under most conditions).

Certain other brands can be more easily serviced but they're of a different construction to Shimano. I've had Hope ones apart a few times, they're a bit more user-serviceable.

[slowster]

If there is no play in the freehub, i.e. side to side movement felt with a finger on the biggest sprocket, the freehub is running well, and there is no reason to believe that there is water inside it, then based on Brucey's past advice I would simply lubricate with gear oil. Brucey has described previously how to do this without removing the freehub body to add oil from the inboard side, and if memory serves I think the way to do it is to introduce oil to the gap between the outer (rotating) part of the freehub body and the hub bearing cone, i.e. maybe best after removing the axle, bearings and any grease which might get in the way. Tilt the wheel so that oil will run down into the freehub, and spin the freehub with your fingers. When the oil has worked its way through the freehub, the pawls will go very quiet.

[Cyckelgalen]

There is one reason to service a freehub, apart from cleaning and lubricating. If there is noticeable play, the bearings can be adjusted and that is done, removing one or more shims. They are of varying thickness and the trick is finding the right combination, the right amount of shims that eliminates bearing pay.

[Brucey]

........There's really very little that a home mechanic can do with it....

IME it is only home mechanics who overhaul freehub bodies; the labour cost is too high otherwise. Inside, they are much like any other freewheel, with just two big differences; 1) nearly everything inside is a bit smaller than normal. 2) one of the hub seals is in the way. Helpfully, you can install a readily available (shimano) seal in most freehubs, and it is not expensive. Shimano originally intended that freehub bodies are overhauled and they accordingly used to sell tools for this, but these days you have to make your own tool, or scour ebay.

Since shimano still make freehubs in much the same way, you can safely assume that they can be overhauled too. Many other brands have built their shimano-esque freehubs in the shimano style, but it isn't always obvious how the freehub body is secured. In particular, if the fastener is accessed via the LHS it is only apparent how it is made once it is apart. The freehub fastener can be a nut or a bolt, on a LH or RH thread and it is in no way clear which it is, or what is the correct direction to turn it. Fortunately you don't always need to know this, because it is nearly always possible to rebuild the freehub body in situ. This is always made easier by the 'cup' being screwed on with a LH screw thread, so this part always unscrews the same way. In just a few minutes, you can reshim the freehub body and provided you can lift the shims cleanly there is no need for a full disassembly.

However, when/if it is all in bits, there are various things you can do (and many of them are relevant to all freewheel mechanisms) as part of a rebuild;

1) replace the balls. Obviously you can buy Gr10 1/8" balls and these will be very good. However if you are a cheapskate, you can (for peanuts) use balls that have come out of a knackered freewheel; these are likely to be more uniform in size than when they went in; being inside a freewheel is a lot like the final stages of manufacturing, in that the wear is concentrated on the larger balls. Provided you don't mix them up (ie. the balls from the inside and outside bearings are always kept separate), then used freewheel balls can make a good alternative to new balls in freehubs.

2) fit a new pawl spring. Pawl springs are usually made from 0.5mm piano wire. You can easily make new pawl springs for virtually nothing.. First take a length of gear housing, of the 4mm OD, slow helix persuasion. Dismantle this, eg. by 'skinning' it. You should be left with a liner tube (which can be v handy for helping feed wire through hidden cable runs) and about 18 lengths of hard wire. This wire is, to all intents and purposes, 'the same' as piano wire, so you can make springs out of it. The procedure is as follows; first make or find a piece of wood whose OD is a bit smaller (by about 20%) than the spring seat inside the freehub body. This is your former. Next, wind one of the wire lengths around the former. Holding the former in a cordless drill can be v. helpful here. You should now have something that looks like a coil spring in the ~0.5mm wire. Now, fit the coil you have just made to a second piece of wood, this time ~+5% larger diameter than the spring seat. Now use a marker pen to make a line along the length of the coil. Once removed from the second piece of wood, the line will be broken up but will still mark the correct points at which the individual springs may be cut off.
If there are two pawls separated by 180 degrees but worked via a single spring (eg. in current SA hubs), the spring should ideally be a non-round shape. However, in a shimano-esque freehub the two pawls are separated by just 120 degrees, so a much simpler circular spring is fine.

3) fit replacement pawls. Obviously the correct pawls are best, but temporarily, pawls salvaged from freewheels might do. Typically these pawls are not as wide, but they may do in a pinch. Replace the pawls in identical pairs only. If the same length as one another, they ought to engage simultaneously. However, they may only do this properly after a period of use, ideally without any free play in the bearings. NB if the teeth in the ratchet are eccentric to the bearings it will never work correctly. You can usually identify this by listening carefully to the pawls as you backpedal very slowly when there is no play in the bearings. If the pawls consistently go 'click-click' instead of 'cliicckk' it means either that the pawls are not quite the same length or that the pawl pockets don't have the correct spacing. If the sound is inconsistent, it means the ratchet teeth are slightly eccentric. It should be possible to correct this by regrinding the bearings, but this will require very precise fixturing.

4) lap the cup for ultra-precise bearing adjustment. There are two slightly different diameters of freehub shim in current use by different manufacturers, and you should avoid mixing them up. In any event, the thinnest shim (which is not always available) is ~50um. It is possible to lap parts to better tolerances than this, so if a shim does not offer sufficiently precise adjustment lapping may offer a route ahead. There are two routes that work, one uses a precise flat surface together with a sheet of abrasive paper (this is how I started out, although it is rather slow), and the other uses the side of an ultrathin cutting disc in an angle grinder. To my surprise, the latter worked very well and was, of course, far quicker. I found it worked best if I reversed the work half-way through the lapping process so that the part remains parallel despite the natural tendency to produce lopsided grinds. I found that I was able to remove about 1um per second this way. Ultimately, I found I was able to lap these parts to ~10um or so, far better tolerances than they were originally made to.
A typical freehub uses a thread of about 700um pitch to secure the LH cup and because of the way the threads are loaded, you can use this as a micrometer screw thread. If you remove one shim too many (eg. using paddle tools made from pieces of squashed spoke), you can see how much further you need to tighten the cup before the bearing free play is eliminated, and (having made a small allowance for free running) how much you need to lap from the parts. Remember that the thinnest shim corresponds to about 18 degrees of cup movement. It is not difficult to do better than this, merely time consuming the first few times you do it.

5) Regrind the bearing surfaces. You can always SG three from four of the bearing surfaces, but doing all four needs the freehub body to be removed from the hubshell. The parts will early always accept a slight grind/polish (ideally leaving a radius just a little larger than the balls), and this can recover freehub bodies which appear to be beyond the pale at first, turning them to 'better than new' condition.

FWIW I think it is probably worthwhile spending the time to remove all free play from freehub bearings, as the wear rate should be reduced subsequently. I would certainly prioritise this over making these bearings super-smooth. You can never completely eradicate wear, but you can often reduce it. Like their hub bearings, the shimano design is intrinsically durable, but get the best out of it requires relatively careful setup/lubrication.

[BarryS]

Excuse the ignorance, but if I go to the trouble to rebuild/adjust my shimano freehub correctly (done that) - how do I add the extra step to surface grind the bearing surfaces? I have the dismantling tools so can get at all four.

[rjb]

I wouldn't go as far as regrinding the freehub bearing surface, just reshim it to reduce excess play. Don't forget when you are pedalling the freehub is stationary, only rotating with the hub. It only turns independently when you freewheel.

[Brucey]

you obviously don't need to regrind the bearing surfaces in most cases, because this bearing either sees load or motion, not both at the same time. Nonetheless, if the freehub is noisy eg because the bearing surfaces are slightly corroded, then a regrind is probably called for. All you need to do this is a dremel tool and an electric drill. See my post 'how to SG' for details.