Rear Hub choice

[SimonCelsa]

I currently have this Shimano XT rear hub fitted to my touring steed; https://www.rosebikes.co.uk/article/shi ... aid:515947.

It has been in use now for about 2 years and approx 8000 miles. Recently I have noticed a "clunk" coming from the freehub every now & then. I removed the freehub with a view to trying to introduce some lube to the innards. I couldn't see any easy way to introduce lube without damaging the seal arrangement and I don't really want to dismantle the unit totally as doubtless I would lose half the balls or knacker it totally...no problem but I don't want the bike out of action for much more than a few hours.

I plan to purchase this rear hub; https://www.rosebikes.co.uk/article/shi ... aid:719994 and build it into a new wheel (my rim needs renewing) utilizing the existing spokes from the XT hub. I would imagine the hub flange dimensions are reasonably similar?! I will then overhaul the XT hub at my leisure and keep it as a spare.

Does anyone have any thoughts on whether this LX hub is much inferior to the XT one?? I am reasonably competent at adjusting cones & greasing hubs so not too worried on that score,

Thanks, all the best, Simon

[Brucey]

the first hub is FH-T780
https://cycle.shimano-eu.com/media/techdocs/content/cycle/EV/bikecomponents/FH/EV-FH-T780-3176_v1_m56577569830758219.pdf

and the second hub is FH-T670
http://si.shimano.com/pdfs/ev/EV-FH-T670-3314.pdf

FH-T670 is built the same way as XT hubs used to be. The newer design of XT hub (eg FH-T780 with the fat axle) is a bit lighter in weight, has less strong bearings with (IMHO) an inferior bearing adjustment system, and has a freehub body which ought to be stronger, but often isn't.

To lube either type of freehub body, withdraw the axle and remove the balls (where possible), leaving the seal in the RH end of the freehub body. Create a puddle of oil in where the RH hub bearings sit. Hold the freehub body in one hand, and spin the wheel. After a while the oil will penetrate the freehub body.

The clunking is either

a) the freehub body about to die.. or
b) there is a little free play in the freewheel bearings and that, combined with the pawl design, makes for a clunk.

On the former point these freehub bodies developed an unfortunate reputation early on for breaking pawls and then smashing themselves to bits. One of the first signs that this is happening is that the freewheel sometimes doesn't freewheel any more, because there are bits of broken pawl floating around inside.

On the latter point the four pawls are set in two opposed pairs. This configuration often knocks when there is a little free play in the freewheel bearings; typically under modest effort in some gears (but not others) there is a knocking that is at twice the wheel rpms.

I would have no qualms about using FH-T670; it is a pretty good hub.

cheers

[SimonCelsa]

OK thanks for that Brucey; I must admit there was a little play in the rear hub when I tried rocking the rear rim this morning so have just tightened up the cones a tad & see how that affects things. I'll still get the cheaper hub though as I'd like to have a spare ready to go,

All the best, Simon

[Brucey]

the bearing play that is most likely to cause clunking is in the freewheel bearings, not the main hub bearings, but you never know. The freewheel bearings are adjustable on shims but this is a bit of a palaver to do.

BTW did you check that the hollow bolt is tight? If not you can get all kinds of weird things happening.

cheers

[SimonCelsa]

I am pretty sure the hollow bolt is tight as I did it up with a pretty hefty allen key. The slight tightening of the cones and associated lock nut has firmed things up nicely, although I do find it pretty hard to find the sweetspot with these hubs....it seems to be very easy to overtighten them and there's only a 'midges' between graunchy bearings & overly slack. see how things go,

All the best, Simon

[Brucey]

one of my gripes about these hubs is that there is no easy means of checking the true bearing adjustment (i.e. with the QR tightened) and then quickly revising the adjustment. You can refit the QR and use washers in place of the dropouts, but it is a major faff to fit and remove these parts between trial adjustments.

cheers