How Bad Is A Cracked Hub??
 

So I ordered new rims for a wheel build. I have to use 120mm hubs, so I unlaced the wheels that were on my bike before. Off I go cleaning away and realize the rear hub has a fracture that stretches about 2/5ths around the hub. After about an hour of hand cramping work I noticed this. I'm assuming this is dangerous and I should find new 120mm hubs?? Itll be a massive pain if so... Just need some conf that I actually have to. Thanks!

I would not use that hub. There's probably something available on Ebay that can replace it.

Why do you have to use a 120mm hub? What prevents you from cold-setting the frame to 126mm or 130mm?

Freewheel hubs lend themselves to axle modifications with various length of axles and spacers..

Stuff a little JB weld into it and keep motoring along.

It depends on the location and nature of the crack. Flanges are under tension and the center under compression. Either way I wouldn't build a new wheel on a problem hub, but if I had a wheel with a crack in the center section, I'd have no qualms about continuing to ride it, though not for starting a long tour.

I wouldn't trust a known-defective component, attempt to repair it nor invest any more effort in it. I don't have any guidance on how to proceed except to pitch the dud hub out right away.

While it is probably best not to use the hub, a picture would help to determine if it's a sure thing to trash it.

Yep, let's see a photo...

=8-)

I would not use that hub. You have several options in replacing the hub. If you can find a stock 120mm hub, you can build a wheel around that. If you find a 126mm hub, you can simply replace the axle with a shorter axle (or trim the existing axle to length), remove 6mm worth of spacers, et voilà! You now have a 120mm hub. Or you can spread the stays to 126mm and use the hub as is.

x2

Being facetious I hope!

Don in Austin

Aluminum + crack on most components usually = trash it.....
Avoiding the expense and time finding a replacement is just not worth risking having that hub asplode on you on the road IMO!

Chombi

You could die from a hub failure. If it's cracked, break it so no one can use it and throw it out. Maybe pry out the bearing cups. There's a chance they may fit another hub.

So do freehubs. If it was me, I'd spread to 126mm and use a 7spd freehub.

Or you could prolly get away with the same hub spaced to 123-124mm. Or even spread to 130 or 135mm, use any number of speeds you like, and enjoy a stronger wheel.

A cracked metal bicycle part equals a broken metal bicycle part. As such it is scrap. A hub, in particular, experiences massive forces at certain points and the crack will enlarge to the point where it eventually fails. No amount of JB Weld or any other bandaid will keep it from happening. You need a new hub.

Drill a small hole in one dust cap, then fill the space between axle and hub and the place where the bearing balls go with black powder, assemble the axle without balls, put some cannon fuse into the hole, light it, throw it, and duck the shards by ducking behind a wall or tree. This is the only thing a cracked hub is good for.

Curious to see a pic.

-G

I fixed it for you! You're welcome!

Don in Austin

While many components made of Alu are in a bad state when cracked if this hub is like the many early Shimano cassette hubs i've seen that are cracked i would not be too concerned about safety issues. Is the crack travelling around the barrel just inside the RH flange? If both the location and brand match the hub will likely spin and otherwise work for a long time. Not to say that this is ideal, just not a short term concern. I've noticed a thin ring of grease on many of these Shimano hubs (the grease weeps out through the crack) but never any flange to flange movement/flex. The wheels are tight and not a trueing problem. The cassettes are always solid in function and don't wobble anymore then typical. I want to say early 1980s alu. shelled 6 speed with twist tooth cogs.


An added aspect is that the axle will act as a through bolt holding any completely cracked hub barrel together, more or less. So bike handling failure mode is an unlikely fate. But the hub is still comprimised and I would replace it as soon as I could. Whether the rim is round and flat (without spoke tension making it so) and therefore worth reusing is another question.


It would help if we had a few good photos to go by. Andy.

+1,000,000,001

=8-)

It wasn't broken. JB Weld is a brand name of a two part epoxy system. Permatex makes the same thing as does Loctite and 3-M. None of that matters because what I said originally is still true. Epoxy won't fix the problem.

The derailleur is held on by a hanger, so it grinds on anything larger than a 126. I would have to realign my facings, and that maybe wouldn't fix it either. And that's well outside of my comfort zone - esp since I just got it powder coated. If I ruin the new coat job, I will be pissed.

http://i.qkme.me/35jwvb.jpg
...

That first part does not compute...

Maybe you should provide not only a pic of the hub, but also the following:

1. Shot of the rear right dropout from the rear - slightly inside so we can see any dropout offset or scalloping.
2. What freewheels you ARE using - AND - want to use.

Also it's entirely possible to do a controlled spread WITHOUT damaging the paint - and with minimal dropout realignment - assuming you do bite the bullet.

=8-)

OK we are actually in agreement. I was just commenting on what total marketing BS it is to call the product a "weld."

Don in Austin