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Bent Axle?

Old 06-03-17, 12:37 PM
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robxcarlson
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Bent Axle?

I'm working on getting an '88 stumpjumper back on the road. I recently regreased the bearings, bought 7 speed freewheel and new chain, put this on today and notices the hub wobbles when I turn the pedals. Is this a bent axle? It didn't look bent, but I don't know what else would cause this.
Here's what it looks like:

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Old 06-03-17, 12:56 PM
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that ain't the hub... that's a lousy, poorly made freewheel.
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Old 06-03-17, 01:00 PM
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That normal for a freewheel , there nothing wrong with your hub or wheel .
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Old 06-03-17, 01:03 PM
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+1, Planar wobble is normal for screwed on freewheels, don't sweat it.
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Old 06-03-17, 03:29 PM
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Freewheel wobble is primarily caused by hub defects.

Most cheap entry level freewheel type hubs will have machining that is off center at one or more locations to various extents.

Freewheel simply inherits whatever hub motion in created as a result.

Search Youtube for Wheels By Fleming - I have a video explaining it.

The effect on the bike and shifting? Little or none...nothing to lose sleep over.

=8-)
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Old 06-03-17, 04:25 PM
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Originally Posted by mrrabbit View Post
Freewheel wobble is primarily caused by hub defects.

Most cheap entry level freewheel type hubs will have machining that is off center at one or more locations to various extents.

Freewheel simply inherits whatever hub motion in created as a result.

Search Youtube for Wheels By Fleming - I have a video explaining it.

The effect on the bike and shifting? Little or none...nothing to lose sleep over.

=8-)
Thanks for the reply. I would assume that this was not a cheap entry level hub for an 88 stumpjumper.
I don't see a name in the hub either, however, everything on the bike is Deore.
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Old 06-03-17, 04:31 PM
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Originally Posted by fietsbob View Post
+1, Planar wobble is normal for screwed on freewheels, don't sweat it.
+1, however the hub doesn't appear to be a Deore. An 88 Stumpjumper hub would have a quick release.
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Old 06-03-17, 04:50 PM
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Originally Posted by maddog34 View Post
that ain't the hub... that's a lousy, poorly made freewheel.
I agree that it's not a bent hub axle. But it's not necessarily the freewheel, either. If the threads on the hub are not perfectly co-axial with the hub axle, it will produce a wobble like that.
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Old 06-03-17, 06:47 PM
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you would have to have taken the wheel off to find out if the axle was bent.
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Old 06-03-17, 08:28 PM
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Originally Posted by skoda2 View Post
+1, however the hub doesn't appear to be a Deore. An 88 Stumpjumper hub would have a quick release.
The rear dropouts are horizontal and I thought QR wouldn't work with those?
The front hub is QR and both rims match, so I think they're original, but I can't be 100% sure.
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Old 06-03-17, 09:11 PM
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Originally Posted by robxcarlson View Post
The rear dropouts are horizontal and I thought QR wouldn't work with those?
The front hub is QR and both rims match, so I think they're original, but I can't be 100% sure.
Modern QRs don't work with horizontal dropouts.

Vintage ones do. (and a few moderns ones that copy old designs)

It's all about progress
when Vertical dropouts became normal, QRs were improved to take advantage by reducing their cost.
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Old 06-03-17, 09:24 PM
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Originally Posted by xenologer View Post
Modern QRs don't work with horizontal dropouts.

Vintage ones do. (and a few moderns ones that copy old designs)

It's all about progress
when Vertical dropouts became normal, QRs were improved to take advantage by reducing their cost.
Thank you for explaining that. I don't have enough familiarity with vintage bikes, but I don't see any reason to assume that the bolt on hub is not original equipment for this bike. Someone with knowledge of specialized from the 80s would need to chime in.
As for the wobble, I guess I'm stuck wth it.
The good news is that there's nothing for me to fix here and I can move on to other parts of the bike.
Thanks again for all the replies and help.
On an unrelated note, I think the rear dropouts might be bent, so that's my next point of investigation....
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Old 06-03-17, 11:11 PM
  #13  
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my '88 or '89 (?) stumpjumper, with original wheels and u-brake, has what look to be shimano 600 hubs. but i would imagine that they called them Deore or something similar. and IIRC they had uniglide freehubs on them.

BTW, i can't see much from the video, except it looks like the entire rear of the bike is wobbling.

Last edited by hueyhoolihan; 06-03-17 at 11:25 PM.
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Old 06-04-17, 12:06 PM
  #14  
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Originally Posted by hueyhoolihan View Post
my '88 or '89 (?) stumpjumper, with original wheels and u-brake, has what look to be shimano 600 hubs. but i would imagine that they called them Deore or something similar. and IIRC they had uniglide freehubs on them.

BTW, i can't see much from the video, except it looks like the entire rear of the bike is wobbling.
It's in a stand, so the wobble may be affecting the whole bike a little.
Does yours have QR rear hub?

As far as the freewheel wobble, I reinstalled the original freewheel and it still had wobble though not as much. From what I read here, I'm not going to worry.
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Old 06-04-17, 01:35 PM
  #15  
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Originally Posted by mrrabbit View Post
Freewheel wobble is primarily caused by hub defects.
For all I know, making the threads 100% parallel is very hard to achieve. The mismatch could be either the hub, or the freewheel, or both. It's very hard to machine the threads so they are 100% centered to the axis.

Have you experimented with switching a freewheel from a cheap, to a higher quality hub to confirm that the hub is the (only) faulty part?
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Old 06-04-17, 02:30 PM
  #16  
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Originally Posted by Slaninar View Post
For all I know, making the threads 100% parallel is very hard to achieve. The mismatch could be either the hub, or the freewheel, or both. It's very hard to machine the threads so they are 100% centered to the axis.

Have you experimented with switching a freewheel from a cheap, to a higher quality hub to confirm that the hub is the (only) faulty part?
I've not done any experiments and I don't have any other 26 wheels to experiment with.
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Old 06-04-17, 03:49 PM
  #17  
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Originally Posted by Slaninar View Post
For all I know, making the threads 100% parallel is very hard to achieve. The mismatch could be either the hub, or the freewheel, or both. It's very hard to machine the threads so they are 100% centered to the axis.
Parallel and concentric threads are not difficult. It's machine shop 101, basic lathe work. The bearing seats should be made very concentric to the hub rims, the same setup could be used to "single point" the freewheel threads. Then the bearings could be installed and used to turn the hub as you drill and countersink the spoke holes. In a well-make hub, everything should be very concentric and parallel with the hub axis.

Regarding the axle, it may well be bent but that cannot be what's causing your wobble. The axle doesn't move. The bearing cones are on the axle that doesn't move. A bent axle could result in your wheel not lining up between your brake pads, or between your chainstays. But it won't cause wheel wobble.

Spin the wheel with the crank so that the freewheel is not "clicking" and is rotating with the hub. Is the hub rim rotating evenly? With the chain on the small sprocket, can you see if the freewheel is wobbling? If the hub itself is wobbling, then whoever made it didn't pass machine shop 101, and you have bearing seats that are not concentric with the hub rims and (probably) the freewheel threads. And you need a new hub. If the hob does not wobble when you use your crank to rotate the wheel (that is, the freewheel isn't clicking), but you see the freewheel wobble (easiest to check viewing the big cog, with a popsicle stick or something clipped to the seat stay) then the freewheels bearings, threads, and/or cog seat was poorly made, or the hub might have its threads not parallel and concentric with the hub axis. New freewheel for the former issue, new hub for the latter.

The technology to ensure concentricity was available in the 1890s, and Sir Joseph Whitworth (namesake of Whitworth screw form, inventor of the surface plate) had measuring devices that resolved down to something like 5 millions of an inch back in 1840 or so. So mfrs had the means to check concentricity.

But it ain't the axle.

Last edited by WizardOfBoz; 06-04-17 at 03:53 PM.
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Old 06-04-17, 06:05 PM
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Originally Posted by robxcarlson View Post
It's in a stand, so the wobble may be affecting the whole bike a little.
Does yours have QR rear hub?

As far as the freewheel wobble, I reinstalled the original freewheel and it still had wobble though not as much. From what I read here, I'm not going to worry.
yes, a QR hub and i use what is probably the original one. no problems holding the wheel.

and although i didn't explicitly state it, mine does not have a freewheel, but instead, a freehub. not that it makes much difference. IME, the cogs often wobble a little on either one. BTW, the rims say SATURNE or something similar on them. i'm sure they are original. it looks like it's a machine welded cromo frame with a big old unicrown fork and shimano oldschool wide cantis. built like a tank.

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Old 06-04-17, 11:29 PM
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Originally Posted by WizardOfBoz View Post
Parallel and concentric threads are not difficult. It's machine shop 101, basic lathe work.
Agree with the rest of your post, just this: I'm not an expert on machining, so I'm not contradicting your claim - just questioning and taking it with a grain of salt, because, from my knowledge, having "investigated" the wobble phenomena, that is not correct, at least for the length and width (diameter) of freewheel attachment mounts.

So, not disputing, more "thinking out loud", please correct me if I'm wrong on any account: frewheel sprockets stand relatively far away from the threads - both laterally and vertically. Making any marginal error seem (more) visible. So 0.01 degree error on a cone might be compensated by material flex and definitely hard to spot with an eye, but if a cone had a 15 T ring attached to it, it might be even visible? Low quality cup and cone hubs let you choose between play and considerable friction that is easily felt when turning an axle by hand on a removed wheel. Higher quality ones are a lot better, but I'm sure even they are not 100% perfect - all comes down to acceptable tolerances and the cost of satisfying them in production. My info is that making freewheel/hub threads so that no play can be seen is very hard. Also, from my knowledge, when something needs to be 100% centered like that, threads are not used for centering - splines or other mechanisms are preferable. Am I correct?

I think every freewheel I've ever seen has some amount of wobble. If what you say is correct, it could be possible (and wouldn't amaze me) that all the manufacturers didn't care much about precision machining - close was good enough for the use and rotating speeds freewheel "sees".

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Old 06-04-17, 11:43 PM
  #20  
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Originally Posted by robxcarlson View Post
I don't see any reason to assume that the bolt on hub is not original equipment for this bike.
The Stumpjumper was a higher-end bike. It definitely would've had QR axles. It also would've had a freehub and cassette, not a freewheel.

I've attached scans from the 1988 Specialized catalog to confirm. The whole catalog can be found at retrobike.co.uk HERE.

Originally Posted by robxcarlson View Post
As for the wobble, I guess I'm stuck wth it.
So long as you're using a freewheel, you're gonna have some wobble.
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Old 06-05-17, 09:37 AM
  #21  
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Originally Posted by Slaninar View Post
I'm not an expert on machining, so I'm not contradicting your claim - just questioning and taking it with a grain of salt, because, from my knowledge, having "investigated" the wobble phenomena, that is not correct, at least for the length and width (diameter) of freewheel attachment mounts.
Slaninar, I take your post as a genuine questioning in good faith, so no offense taken.

I grew up working in my Dad's machine shop, and studied engineering. Not an expert, but I have some knowledge.

Round stuff is often made on a lathe. In the old manual process, you'd fasten work to the "spindle" (the thing that is connected to a motor and spins on bearings to rotate the work) using a chuck. The chuck is not perfect, and the round piece may be off-center (known as "run out"), but if you use the lathe to cut the outer diameter off your raw stock, the turned portion is round and rotates perfectly on center. Any further cuts (recesses for bearings, threads for freewheels, rims to accept spokes) you make without taking the workpiece out of the chuck remain perfectly on center. So you should be able to get a lot of a wheel hub, for example, very concentric. Within a 0.001 or so (or better). This amount of runout would not be noticeable even with the geometry points you correctly note. If you have to take the workpiece out and rechuck (for example, to machine the NDS after you've machined the DS) it you can get into trouble. Rechucking in a worn old "three jaw" chuck that use a scroll to control all jaws at the same time can give poor results. You can be off-center, and the work can end up not parallel with the other work features you've turned in the work. You can get good results by centering the workpiece using a "four jaw" chuck with individually adjustable jaws, but this takes time and expertise.

Modern production is done using automated machining centers, and these should give you work with almost no measureable non-concentricity.

I've never had a freewheel or hub that was off by much, but you've had a different experience. A freewheel made with care, by experts, should not show wobble.

Last edited by WizardOfBoz; 06-05-17 at 10:41 AM.
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Old 06-05-17, 09:50 AM
  #22  
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Originally Posted by WizardOfBoz View Post
I've never had a freewheel or hub that was off by much, but you've had a different experience. A freewheel made with care, by experts, should not show wobble.
Thanks for elaborating that.

You are correct about quality production - most freewheels I've come across were (lower end) Shimano freewheels, on lower end Shimano, or "no name" manufacturers' hubs. All had wobble.

Other equipment made by Shimano, even lower end stuff was always of decent quality - hubs, cassettes, derailleurs... Don't understand why they would allow for wobbly freewheels, unless manufacturing straighter ones was more expensive/time consuming? It doesn't affect function, but looks bad IMO.
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Old 06-06-17, 09:06 AM
  #23  
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Originally Posted by SkyDog75 View Post
The Stumpjumper was a higher-end bike. It definitely would've had QR axles. It also would've had a freehub and cassette, not a freewheel.

I've attached scans from the 1988 Specialized catalog to confirm. The whole catalog can be found at retrobike.co.uk HERE.



So long as you're using a freewheel, you're gonna have some wobble.
The text is fuzzy - but I can tell from it that I don't have the original wheels. My current wheels match and I made the assumption that the bolt on rear wheel was consistent with the horizontal dropouts.

So, I can keep my current wheels and live with them for now - or I can find a higher quality wheelset, either the original wheels or something current that is the right size for this bike.
I found a listing on eBay for vintage gx23 wheels with Deore hubs that would cost $130 shipped. I'm assuming that those would be the original wheels or close to it. Opinions? What new options might exist that don't require resizing the rear triangle?
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Old 06-06-17, 03:17 PM
  #24  
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Originally Posted by robxcarlson View Post
What new options might exist that don't require resizing the rear triangle?
It's a steel frame
new hubs are only 5mm wider.
just shove it in there
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