Thru axle torque and bearing loading Shimano Hubs

[brucelee]

I've just had a pair of RS770 (Ultegra, disc) wheels delivered and am setting them up. There was a post on another thread (I started about buying a tub wheel) that said that through axle torque had no effect on the bearing setup for thru axle hubs. So I put the wheel in, nipped up the axle and gave it a spin.... As I increased the torque on the axle, the wheel slowed down more and more. At 7Nm, the wheel quickly came to a stop. How should I interpret this ?
Cheers,
Bruce.

[slowster]

According to Shimano the hubs have a 'hub axle unit' which appears to function in the same manner as a QR hollow axle. So it seems that when the thru axle supplied with the frame/fork is tightened, it will potentially compress the hub axle unit, and thus create the same need to allow for that when adjusting bearing pre-load as with QR hubs. Page 13 of the dealer manual describes the use of the spanner flats on the hub axle unit's integral cone on one side and the lock nut and adjustable cone on the other side to adjust play, but makes no reference to the need to leave a little bit of play which should then disppear when the wheel is fitted in the frame/for and the thru axle tightened.

Interestingly there is only an adjustable cone and lock nut on one side of the hub axle unit. The cone on the other side is part of the hub axle unit itself. On the rear freehub the adjustable cone and lock nut are on the non-drive side, but on the front they are on the drive side. Brucey has often pointed out that precession of the cone is a bigger risk on the drive side, because it causes the cone to tighten and potentially damage the bearings and bearing surfaces. For QR hubs Brucey's recommendation was to use threadlock to semi-permanently lock together the drive side cone and lock nut, and use the non-drive side cone and lock nut to adjust and maintain the hub. Maybe the hub axle unit of Shimano's thru axle cup and cone hubs can be rotated so that the fixed cone is on the drive side, but if that were possible I would have thought that would be how Shimano would specify it were assembled.

https://si.shimano.com/pdfs/ev/EV-FH-RS770-4243.pdf

https://si.shimano.com/pdfs/dm/DM-RAHB002-01-ENG.pdf

[TheBomber]

Nice explanation slowster. Unfortunately I'm not sure Shimano's service document is so well written. The text on page 13 almost seems to be saying that the hub axle unit has a LH thread (to deal with the precession issue). But the bullet points beneath it contradict the directions to be turned.

[slowster]

The text on page 13 almost seems to be saying that the hub axle unit has a LH thread (to deal with the precession issue). But the bullet points beneath it contradict the directions to be turned.

Well spotted:

Install the hub axle (A) into hub as in the illustration.While holding the LH cone nut with 15 mm hub spanner (B), use the 20 mm hub spanner (C) to tighten (y) or loosen (z) the RH side cone for rotation feeling adjustment. Using another 20 mm hub spanner (C), tighten (x) the RH lock nut so as to double-lock the mechanism.

(x) Tighten
(y) Loosen
(z) Tighten

I did wonder if it might be a LH thread for the front hub axle unit, because on page 14 it makes a point of stating that the rear hub cone and lock nut are clockwise thread, and I thought that the only reason to state that would be if the front was different, but there is no corresponding text stating what the front hub axle unit thread is. Incidentally the diagram at the top of page 12 also shows normal RH thread to tighten the lock nut.

Perhaps the OP would be so good as to confirm what the thread is on his front hub axle unit.

[PT1029]

All very useful thank you.

https://si.shimano.com/pdfs/ev/EV-FH-RS770-4243.pdf
p1:
Part 3 5/32" balls, picture says 16 balls, list says 34
Part 4 "ball retainer 3/16" "

https://si.shimano.com/pdfs/dm/DM-RAHB002-01-ENG.pdf

p5. • " If the wheel becomes stiff and difficult to turn, lubricate it with grease". A little simplistic possibly!
p13 LH threaded cone, RH threaded lock nut (front hub)
p14 + 15 "clockwise thread" for cone and lock nut (rear hub) (it would have helped if they had used the term "counter/anti clockwise thread on the front hub, p13).
p15. LHS 15 X 5/32" balls (z) RHS 16 X 5/32 balls (y)

So,
Rear cone/lock nut RH thread, F cone LH tread (for good reasons)/RH thread lock nut.
different ball sizes LHS/RHS in the front hub
different numbers of balls LHS vs RHS rear hub.

What could possibly go wrong?!!