Bicycle Mechanics - arsed axle, or blown hub?

hiya. this is gonna sound like a complete idiot question but i am really kinda stumped.

i have bike. the bike has a rear wheel. when i put the bike and the wheel on the bike trainer today i noticed that in a certain gear i could hear a clicking/thumping sound, and felt it through the pedals. i thought at first it was the BB but by concentrating on the rhythm found it to be the rear wheel. this drew my visual attention thither and i noticed that the rear hub oscillates up and down on the freewheel side. (the FW dances a bit too but i know that's normal) i made sure the hub was moving and not just the FW. preliminary diagnosis--bent axle.

so...i pulled the axle tonight and rolled it on a flat surface. it really didn't seem bent. so i reinstalled and of course the wheel's behaviour hasn't changed a bit.

so, is it possible that the axle is bent enough to do that to a wheel but not enought to see/detect? AND--is it possible the innards of the hub are buggered up somehow? the cones? the bearings? the hub really looks fine. the way the wheel is acting on the bike really says bent axle. ie: the axle stays still while the hub oscillates around it.

i appreciate your help! mark

A bent axle wouldn't cause this.
Even if it's bent, it's always in the same position, since it's "fixed".
It has to be a rotating part(s).

A bent axle wouldn't cause this.
Even if it's bent, it's always in the same position, since it's "fixed".
It has to be a rotating part(s).

hmmm. ok, so i can see that if the axle is bent, it still just sits there, which is exactly whats happening when i look at the hub and axle as the wheel spins: the axle doesn't move. so the hub, if it is straight, will just rotate around that stationary axle and appear stationary as it spins, yes? so the fact that it oscillates means there is an irregularity in, say, a race--maybe something threw it out of round?

could mismatched bearings also cause this? or a skewed cone? really trying to understand the physics here.

thanks!

I can't imagine a bent axle only giving symptoms in one gear. I would clean and lube your freewheel.

I can't imagine a bent axle only giving symptoms in one gear. I would clean and lube your freewheel.

it makes the "clunking" sound/vibration in all gears, but one in particular, with a certain cadence, really amplifies it. its as if the harmonic resonance between the cadence of the pedals and the wheel's turning just mesh somehow. so it gets louder and more pronounced in that particular gear. it's still present in the other gears, though! the sound/vibration is definitely lining up with the rotation of the wheel, and NOT with the rotation of the pedals, though...

oh and the freewheel is newly cleaned and lubed. :thumb:

A loose or bent freehub fixing bolt? What kind of hub is it?

If it's a freewheel hub, maybe the freewheel threading is coming apart from the rest of the hub body like in this thread http://www.bikeforums.net/showthread.php?t=505037

A loose or bent freehub fixing bolt? What kind of hub is it?

If it's a freewheel hub, maybe the freewheel threading is coming apart from the rest of the hub body like in this thread http://www.bikeforums.net/showthread.php?t=505037

its a freewheel, sorry if i said it was a free hub. not sure the make, but it's laced to a Weinmann R-19 rim. nice wheel. i'll be sad if it is gonzo. :cry:

i'll check on the make when i get home from work. also gonna examine it closely for damage.

EDIT: also, would that cause the whole hub to oscillate? seems to me just the end would be wonky in that case...

It has to be one or more of-
Hub, cone or bearings.
Is the noise possibly every 2 revolutions? If so I'd say BB's.
Yos simply have to disassemble and inspect.
You might want to buy 18, 1/4" BB's (and grease?) from the LBS before you start.

ok update:

i took the wheel apart, freewheel and all. i took a ruler that measures to 32nds of an inch and measured the disance from the outside (highest) edge of the bearing races to the outside edge/face of the hub. turns out that the freewheel side race is not seated evenly. its a difference of 1/32" from one edge to the opposite edge.

one thing i did think of maybe related to the original problem of the clicking/thumping noise--when i have the bike on the trainer it seems alot more stress is put on the drivetrain than if the bike were on the road. for example--on another bike, i had trouble shifting into the biggest chainring when the roller was engaged, but when it was disengaged it shifted fine. i haven't had a chance to test this theory on the bike currently in question, (the theory being that the stress of the trainer exacerbates these minor problems and causes other ones) but i wonder would it be an issue at all w/o the added sress on the drive train. am i way off here or has anyone else noticed this about trainers? or do i just have a crappy trainer, maybe?