Author Topic: Wobbly cogs  (Read 300 times)


  • Most of me survived the Pennine Bridleway.
Wobbly cogs
« on: June 29, 2020, 07:40:57 pm »
Today I was just about to pop the rear wheel off our tandem to change the tyre when I spotted this:

I'd previously spotted that it had a bent axle but I though that would just mean the wheel didn't sit quite true in the frame, I wasn't expecting this!  So I dismantled the hub and verified that the axle is indeed bent.  Not only that, the drive side cone is so badly manufactured the I can see the faces wobbling as it is run down the axle.  The hole through it isn't drilled square to the faces.  But having got it all on the bench and found a replacement axle & bearings online (not found the cones yet) I'm having doubts that I've found all bent parts.  Wouldn't something on the wheel need to be out of kilter to get this effect?  Perhaps the race out of true?  The rim runs remarkably true.

The only marking on the hub is hero.
2020 targets: None
There is only one infinite resource in this universe; human stupidity.

Re: Wobbly cogs
« Reply #1 on: June 29, 2020, 10:13:58 pm »
Freewheel hub on a tandem "they all do that , sir". Probably no more than the axle bent and then the cones rubbing a bit. A cassette hub Shimano style with bearings further outboard would support the axle better.
I don't know Hero hubs but they do do (or did) BSO level Shimano clone budget freewheels.
Someone will come along and say that the bearing shells are probably shot but a bent axle on that style of hub on a tandem would be par for the course (which is how I come to have a hub with an 11mm axle).

Re: Wobbly cogs
« Reply #2 on: June 29, 2020, 11:12:44 pm »
bent axles on a tandem were always a thing BITD when it was screw-on freewheels or nothing.  If you are able/willing to do a little fettling you can very greatly improve things (at low cost vs installing a freehub) by installing an 'outrigger' bearing (on a straight axle).  I've written this up (just today) here

This is to be used on 'workhorse' bikes such as tandems, and utility bikes using SA X-RD rear hubs. It can of course also breathe life back into notions of using classic screw-on freewheel hubs without the attendant risk of axle trauma.

I've yet to figure out the best way for freewheels other than those which use a shimano-style extractor spline though; these will need a different outrigger bearing.


Re: Wobbly cogs
« Reply #3 on: June 29, 2020, 11:37:31 pm »
I forgot to say that with some (perhaps many) screw-on freewheels the interface between hub and freewheel can be less than optimal; i.e it screws on wobbly  :facepalm: This was something that held up Sachs efforts to produce a pro transmission and groupset in the early 90's. Some pros complained that the cogs on a Sachs ARIS freewheel wobbled compared to the cassettes of Campa and Shimano.

Re: Wobbly cogs
« Reply #4 on: June 30, 2020, 12:06:05 am »
it is worth mentioning that BITD I wanted to install outrigger bearings inside SunTour freewheels, but didn't because the centre bores didn't ever run perfectly true.

FWIW I have had a few shimano freehubs where the freehub body didn't run perfectly true either. On several occasions I have dug in and located the cause; burrs on the washer between the freehub body and the hubshell.

With a cheap hub and cheap freewheel, almost anything could be happening.



  • Most of me survived the Pennine Bridleway.
Re: Wobbly cogs
« Reply #5 on: June 30, 2020, 07:19:15 pm »
Thank you all for the reassurance.  I've ordered a shimano freewheel remover, I'll strip it right down and see if there's anything obvious.

The outrigger bearing is possibly beyond my skill with a grinder, I'd need a much larger tube of bearings to wreck.

Found a complete axle on sjs for peanuts.  I'll give the cheap option a go once and if it quickly fails try something else.
2020 targets: None
There is only one infinite resource in this universe; human stupidity.


  • Whimsy Rider
Re: Wobbly cogs
« Reply #6 on: June 30, 2020, 07:59:06 pm »
Bending the axle does nothing regarding the runout of the freewheel, as you expected.

Does the drive side flange wave side-to-side when the hub rotates? Unlikely but if so, the hub shell is deformed. If the wheel has been trued up since the hub deformation occurred, the rim can still run perfectly true.

Potentially the freewheel thread on the hub could be axially misaligned with an undeformed hub shell. Unlikely but if so, that should be pretty obvious (after removing the freewheel) by spinning the wheel and observing runout of the hub threads.

The freewheel might be poorly manufactured with its freewheel thread axially misaligned with the freewheel body (difficult to check). Otherwise (and most likely) the manufacturing tolerances of the freewheel bearings are too great. Given the cost, I would just replace the freewheel (and chain if noticeably worn) with a more consistently made freewheel.
Wheel meet again, don't know where, don't know when...


  • Professional Gobshite
  • Just a tart for retro kit . . .
    • John's Bikes
Re: Wobbly cogs
« Reply #7 on: June 30, 2020, 08:49:42 pm »
I don't know how old your tandem is or if it's paricularly historic or precious but, pressed steel hubs? In the 21st century? That's BSO tackle.

If that was me, I'd bite the bullet and get the wheel rebuilt on a cassette hub. At the very least you won't bend the axle again...

Well that's the more blunt way of putting it but as usual he's dead right.