Stripped axle threads

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gbnz
Posts: 1813
Joined: 13 Sep 2008, 10:38am

Stripped axle threads

Postby gbnz » 25 Jul 2020, 8:22pm

Just wondering if anyone has experience of the threads stripping off the axle mid-ride? It's not a problem, just wondering why it did it :?

It's a rear wheel, 36 spoke Rigida Sputnik, c/w Shimano LX Deore freehub purchased six years ago inJuly '14. Specific reasons have resulted in low, limited miles commuting, winter, wet weather use and minimal heavily loaded touring. And so, I'd resisted the temptation to clean it out and regrease, since at least the end of 2016!

Perfectly ok for 270 odd miles last week (Nb. For some some reason a high mileage week!). Then suddenly on taking a bend in the road yesterday at a fair speed (NB. 18-22mph) I felt a distinctive wobble! Wasn't quite sure if it was me, but 7 miles down road, only 2 miles left, I felt it necessary to do a full visual check of tyres/spokes/excess hub play, prior to a long descent. Thought it might be a heavily worn rear tyre. But, nothing notable.

But 2 miles into the ride today, the gradient flattened out and I sped up. For a couple hundred metres. It was clear something was happening somwhere, on a wheel, frame or bottom bracket.

Took a slow 10-12 mile leisure route home. Stripped the rear wheel to start, lock nut quite easily a good 2mm loose, a spiral of metal coming of the axle. Thread partially stripped, but why? Have to admit I've never thought that axles spontaneously being stripped if the thread would be an issue, mid ride or tour.

Brucey
Posts: 39933
Joined: 4 Jan 2012, 6:25pm

Re: Stripped axle threads

Postby Brucey » 25 Jul 2020, 8:28pm

if one cone or locknut is loose then 'precession' can act on the parts and cause movement/damage, so it might have been that. IME this is far more likely to occur in frames with vertical dropouts, because the QR doesn't seem to need tightening to the normal amount. Yet insufficient tightening of the QR is exactly what can start cones and locknuts moving around.

The most destructive events of all can occur when the RH cone and locknut are not tight; the effects of precession can extend as far as entirely wrecking the hub.

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

gbnz
Posts: 1813
Joined: 13 Sep 2008, 10:38am

Re: Stripped axle threads

Postby gbnz » 25 Jul 2020, 8:48pm

Brucey wrote:if one cone or locknut is loose then 'precession' can act on the parts and cause movement/damage. IME this is far more likely to occur in frames with vertical dropouts, because the QR doesn't seem to need tightening to the normal amount. Yet insufficient tightening of the QR is exactly what can start cones and locknuts moving around.

The most destructive events of all can occur when the RH cone and locknut are not tight; the effects of precession can extend as far as entirely wrecking the hub.

cheers


Brucey thanks. I can say categorically that the QR was rock solid - though have to say that I'm aware that I do overtighten stuff (NB. Though only managed a 130kg lat pull at the gym this morning, it having been closed for four months :( ).

The rear wheel hadn't been removed fo months/even years? I'll have to check on the purchase date of the tyre (NB. Heavily worn), as that's the last date it'll of been disturbed.

Brucey
Posts: 39933
Joined: 4 Jan 2012, 6:25pm

Re: Stripped axle threads

Postby Brucey » 25 Jul 2020, 10:16pm

If the QR was tight to undo but hadn't been disturbed for a long time, might it have been corroded and partially seized in the cam, and thus not actually gripping as well as the force to release it might have suggested? In any even that a locknut wasn't tight is a surefire sign that something was wrong there....?

Was it the LH locknut or the RH locknut?

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

gbnz
Posts: 1813
Joined: 13 Sep 2008, 10:38am

Re: Stripped axle threads

Postby gbnz » 26 Jul 2020, 8:40am

Brucey wrote:If the QR was tight to undo but hadn't been disturbed for a long time, might it have been corroded and partially seized in the cam, and thus not actually gripping as well as the force to release it might have suggested? In any even that a locknut wasn't tight is a surefire sign that something was wrong there....?

Was it the LH locknut or the RH locknut?

cheers


Thanks, no corrosion visible though the inner workings of the cam can't be seen (Nb. Though there's no sensation of stifness or excess mvt in the working of the QR lever). The wheel hasn't been removed or any part of the freehub touched in the past 2 Yr's & 90/97 days (NB. Tyre ordered 2 Yr's/99 days ago)

Though the movement in the locknut appeared to have been the LH locknut on first glance, on reflection it's the RH locknut which has moved. Never mind, got a spare freehub in stock and the workings of another, so fairly straightforward to sort it.

Brucey
Posts: 39933
Joined: 4 Jan 2012, 6:25pm

Re: Stripped axle threads

Postby Brucey » 26 Jul 2020, 8:44am

I think it is not a bad idea to use (strong) threadlock on the RH cone; this ought to reduce the chances of precession and consequent hub issues. If the hub survived precession more or less unscathed, you can consider that you dodged a bullet there; I have seen hubshells crushed wholesale when the RH cone has precessed.

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

Pebble
Posts: 117
Joined: 7 Jun 2020, 11:59pm

Re: Stripped axle threads

Postby Pebble » 26 Jul 2020, 10:15am

I was once with someone who had recently rebuilt his rear hub (after 20+miles) all of a sudden his rear wheel locked solid, it appeared to me that the RH cone had wound itself into the hub? my guess was the lock nut had not been tightened enough?

It has always since been in the back of my mind if that had been the front wheel -


so would it be precession that started the fail off, then when sufficiently tight doe's the friction from the bearing cause the catastrophic tightening?

would a LH cone just work itself loose - and hence be a much safer failure.

iandusud
Posts: 382
Joined: 26 Mar 2018, 1:35pm

Re: Stripped axle threads

Postby iandusud » 26 Jul 2020, 10:20am

Back in the day... many hubs were assembled with a fixed r/h cone so that only the l/h cone was adjustable to avoid this potential catastrophic failure. You just needed to be sure to fit your front wheel the right way round, particularly if the adjustable cone didn't have a locknut which was common practise (relying on the wheel nut to secure the cone against the dropout). I've seen a few front hubs wrecked due to this.

gbnz
Posts: 1813
Joined: 13 Sep 2008, 10:38am

Re: Stripped axle threads

Postby gbnz » 26 Jul 2020, 11:39am

Brucey wrote:I think it is not a bad idea to use (strong) threadlock on the RH cone; this ought to reduce the chances of precession and consequent hub issues. If the hub survived precession more or less unscathed, you can consider that you dodged a bullet there; I have seen hubshells crushed wholesale when the RH cone has precessed.

cheers


Thanks, for some reason I've never considered using threadlock on the cones (NB. Though I use it elsewhere, may be because of the need for grease/adjustment when assembling hubs). Though a practice I'll now use on the cones/locknuts

And in respect to catching it in time, I'm pleased to have caught it. I was sure something wasn't right on the bend; though nothing was apparent on the next several miles on a slow ascent & a restricted 20 -22 mph descent (NB. I routinely hit 40mph on that stretch). I checked it in detail prior to the descent; rims, spokes, hub play, tyre surface/sidewall's/bead, handlebar stem, crankset loose?. And given that I'm now collapsing on the bike (13 No. emergency ambulance rides in two years) there was a good chance it'd been a mini brain seizure.

But no; 2.5 miles on a slow uphill ascent the next day, absolutely nothing apparent. But within 200 metres on a flatter/higher speed run, it was clear that something wasn't right. I suspected a locknut or Rr tyre sidewall failing (NB. Tyre being heavily worn/flexibe). But apparent immediately that it was the locknut

Pebble
Posts: 117
Joined: 7 Jun 2020, 11:59pm

Re: Stripped axle threads

Postby Pebble » 26 Jul 2020, 12:19pm

iandusud wrote:Back in the day... many hubs were assembled with a fixed r/h cone so that only the l/h cone was adjustable to avoid this potential catastrophic failure. You just needed to be sure to fit your front wheel the right way round, particularly if the adjustable cone didn't have a locknut which was common practise (relying on the wheel nut to secure the cone against the dropout). I've seen a few front hubs wrecked due to this.

I always do the RH cone in the vice so I can be sure it has been locked correctly - I then do the adjustments on the LH so as if any mistakes are made it shouldn't be causing a lock up scenario.

Cyckelgalen
Posts: 86
Joined: 21 Sep 2018, 11:29am

Re: Stripped axle threads

Postby Cyckelgalen » 26 Jul 2020, 1:41pm

I've had several RH cones working loose and causing severe damage to the races and bearing balls but never to the thread, and that includes one of the new XT M785 hubs with aluminium axels and much softer threads. After these incidents I am convinced that threadlocking the RH cone and locknut is absolutely necessary and the only reason why I haven't done it so far is that during regular hub maintenance/adjusting everything gets smeared in grease and i presume that the treadlock won't have any effect unless you manage to keep the threads on axel, cone and nut surgically clean. Not an easy thing to do, as there will be already traces of grease in the thread between the cone and axel and you will smear that all along the axel when you take it off the hub. Another issue is that adjusting may require tightening and loosening the cones several times and theadlock, as many adhesives, are designed to be left in place without movement while they set.

Many of these shimano hubs with aluminium axel actually have the RH cone fixed onto the axel, I suppose they a are treadlocked at the factory before any grease is applied. If they use a river or any other mechanical solution to fix the RH cone, it is not visible.

Brucey
Posts: 39933
Joined: 4 Jan 2012, 6:25pm

Re: Stripped axle threads

Postby Brucey » 26 Jul 2020, 2:56pm

gbnz wrote:
Brucey wrote:I think it is not a bad idea to use (strong) threadlock on the RH cone; this ought to reduce the chances of precession and consequent hub issues. If the hub survived precession more or less unscathed, you can consider that you dodged a bullet there; I have seen hubshells crushed wholesale when the RH cone has precessed.

cheers


Thanks, for some reason I've never considered using threadlock on the cones (NB. Though I use it elsewhere, may be because of the need for grease/adjustment when assembling hubs). Though a practice I'll now use on the cones/locknuts....


it is normally only required on the RH cone/locknut, since all precession usually does on the LH side is to drive the LH cone tighter against the locknut. Since this makes the hub bearing adjustment slightly looser rather than a lot tighter (as happens with a loose RH cone) this is normally fairly harmless.

FWIW most threadlocks will tolerate a small amount of oil. The correct RH setting can be achieved by careful measurement, with subsequent bearing adjustment via the (unthreadlocked) LH cone/locknut.

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

gbnz
Posts: 1813
Joined: 13 Sep 2008, 10:38am

Re: Stripped axle threads

Postby gbnz » 31 Jul 2020, 7:37am

Hmm, the threadlock I've got seem's a bit too weak. Had a 100 odd miles this week and am fairly sure the RH cone et al are moving.

So a bit of Expoxy Resin beckons. Ten years or so since I used it, but kept a damaged bottom bracket in running order under a demanding daily mileage for a good 2-3 years. I presume the freehub will need to be scrapped when when the RH cone wears out, but should be a while

Brucey
Posts: 39933
Joined: 4 Jan 2012, 6:25pm

Re: Stripped axle threads

Postby Brucey » 31 Jul 2020, 8:24am

heat will degrade epoxy resin such that you will be able to remove a worn cone from the axle should the need arise.

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