Rear derailleur falls off

BiggMakk said:

I ordered a bike on Ebay. It came in near-new condition, except I believe the rear derailleur or drop-out treading got damaged during shipping. When the rear quick-release is locked everything works just fine. But when I remove the rear wheel I notice that the derailleur jiggles and with just a bit of pushing, falls off. It’s an Ultegra derailleur with 2 Allen bolts that attaches to the drop-out. It may be caused by one of three possibilities:

Is the drop-out supposed to be threaded because there seems to be no threading - the Allen bolts slide in with little resistance? Could the threading have been wiped out during the damage?

The Allen bolts don’t seem to tighten the derailleur once connected to the drop-out; they just spin. But when I test the bolts directly on the derailleur without the drop-out, it tightens fine.

May be the derailleur attachment got bent so it’s not sitting flush on the drop-out. I suppose it will never fully tighten because of the bend.

I’d like to know how tech-experts would remedy before I take it to a LBS (the ones in my neighborhood are run by clowns). Thanks.

Sounds like your derailleur hanger is the problem. On some frames the derailleur hanger is part of the frame and on others it is a replaceable piece of aluminum. The derailleur itself only has one allen bolt to attach it to the dropout or derailleur hanger. My guess is that the holes that the screws that attach the derailleur hanger to the frame are stripped and that the quick release holds the whole thing together. It is probably fixable, but you may need to find an LBS that is not staffed with clowns.

Look at the park tool website pictures to see which part you have a problem with.

http://www.parktool.com/repair/readhowto.asp?id=39

John M, thanks for your response. I did not realize the hanger was separate from the derailleur. In that case, the threading on the hanger works fine (as I separately tested it without the drop-out). Could it be the drop out threading that's stripped? Are drop-outs threaded? Sounds like an exensive, if not impossible, fix.

BiggMakk said:

John M, thanks for your response. I did not realize the hanger was separate from the derailleur. In that case, the threading on the hanger works fine (as I separately tested it without the drop-out). Could it be the drop out threading that's stripped? Are drop-outs threaded? Sounds like an exensive, if not impossible, fix.

If your frame has a replaceable derailleur hanger, and it sounds like it does, then you may be correct that it is the dropout (frame) that is stripped. If so, a good mechanic or frame builder can probably rethread it for you.

I think that your next step is a good shop for an expert opinion. Alternatively, you might call the people at this link since derailleur hangers is what they do:

http://www.derailleurhanger.com/

Ah, the perils of eBay. Hopefully the hassle was offset by the savings you made.

John M said:

If your frame has a replaceable derailleur hanger, and it sounds like it does, then you may be correct that it is the dropout (frame) that is stripped. If so, a good mechanic or frame builder can probably rethread it for you.

I think that your next step is a good shop for an expert opinion. Alternatively, you might call the people at this link since derailleur hangers is what they do:

derailleurhanger.comderailleurhanger.comOpen ↗

Ah, the perils of eBay. Hopefully the hassle was offset by the savings you made.

I'd agree with the other guys. On a slightly different note, unless you see obvious signs of damage to either the box or the bike itself, I'd dare say the seller sold you the bike with pre-existing damage. I can't imagine the threads themselves getting stripped out somehow during through rough handling during shipment without obvious signs of trauma to the carton or bike.

The carton was in a very poor condition. I think it was not an eBay issue but an UPS one. Anyway, it's too late to put a blame...I need to get this fixed. If a good bike shop rethreads the dropout, will I need to use wider Allen bolts? And will that in turn affect my hanger? Thanks.

BiggMakk said:

The carton was in a very poor condition. I think it was not an eBay issue but an UPS one. Anyway, it's too late to put a blame...I need to get this fixed. If a good bike shop rethreads the dropout, will I need to use wider Allen bolts? And will that in turn affect my hanger? Thanks.

Yes to repair the thread drilling and tapping to a bigger size is one option. but i thought it worth mentioning that a thread repair kit may do the job, i know you wont know what that is but any engineering shop will. and repairing threads is more an engineer or mechanical fitter job. if i were you i would visit a local engineering shop and ask. im a mechanical techinician and could repair that type of job in 10 mins, so you should get away cheap. good luck

I found a very good bike shop (run by real bike riders - no hybrids and kids's bikes sold at this shop). They had never seen a problem like mine before but upon inspection said that the treading on the first few mm's of the hanger was stripped, and that's why the Allen bolts were not catching. A simple solution: a new hanger.

I just ordered a hanger from the bike company. Hopefully this will fix it. However, I still am not sure if the dropout is supposed to be threaded.

BiggMakk said:

I found a very good bike shop (run by real bike riders - no hybrids and kids's bikes sold at this shop). They had never seen a problem like mine before but upon inspection said that the treading on the first few mm's of the hanger was stripped, and that's why the Allen bolts were not catching. A simple solution: a new hanger.

I just ordered a hanger from the bike company. Hopefully this will fix it. However, I still am not sure if the dropout is supposed to be threaded.

I don't understand this - the hanger bolts thread into the frame dropout, not the hanger itself. Surely the dropout threads need repair or retapping, not the hanger replaced??!!

I really don't know the answer...but will find out when the new hanger arrives. Mechanically I suppose the hanger can stay put with just its own threading as long as the Allen bolts tighten properly.

BiggMakk said:

..They ...said that the treading on the first few mm's of the hanger was stripped, and that's why the Allen bolts were not catching. A simple solution: a new hanger.

This doesn't make sense. Please add some pictures or do some reading to check that you've gotten your terminology straight.

An RD attaches with ONE(1) Allen bolt to a hanger, except for low-end stuff that comes complete with a slotted tab that hooks on to the wheel axle and is held in place by the wheel lug/skewer.
Or are you saying that the screws holding your removable der hanger in place has the heads on the inside of the dropout? (which would be possible, but not something that I've seen before.)

The wheel slots are never threaded, holes for fenders/racks might be threaded, der hanger is always threaded.
You can't use a screw to attach two threaded objects to each other unless they can be rotated with reference to each other, which shouldn't be the case with a removable der hanger. If you have a removable hanger with the threads in the hanger then the corresponding holes in the dropout definitely shouldn't be threaded.

In response to 'dabac,' I have created a quick diagram (I do not have access to my bike at the moment). From what you are saying, the dropout is never threaded; then I should be fine with a new hanger. I hope that is the case. Thanks.

BiggMakk said:

In response to 'dabac,' I have created a quick diagram (I do not have access to my bike at the moment). From what you are saying, the dropout is never threaded; then I should be fine with a new hanger. I hope that is the case. Thanks.

So the bolt heads are on the inward side of the dropout - this makes everything make sense. (My bikes are not like this - the heads are facing outward from the hanger side.)

BiggMakk said:

...I have created a quick diagram (I do not have access to my bike at the moment).

(Agreeing with artemidorus)

The diagram explains everything. You have smooth holes in the dropouts and the threads in the hanger. Somewhat unusual, but fully doable.
It actually makes more sense to have the threads in the replaceable part rather than in the dropout, since threads do get damaged every now and then.(although der hangers aren't a high-service item...)

BiggMakk said:

... From what you are saying, the dropout is never threaded ...

No, what I'm saying is that you can't have both threaded. Either or is fine(and on your bike apparently the threads are in the hanger), but not both. If both were threaded the screws would no longer be able to squeeze the hanger firmly to the dropout.

BiggMakk said:

... then I should be fine with a new hanger.

Sure, you're simply replacing a damaged part designed to be replaceable.
Since Hex keys usually comes in an L-shape the other dropout won't be too much in the way at assembly anyhow. Fitting a screwdriver might have been awkward...

There should be a reason for the threads stripping in the first place, so be careful at assembly. Check that the screws will fit properly in the hanger before mounting it to the frame, also make certain that they're the right length. If the ends(not the heads!) protrude a little is a minor aestethic issue that's far better than if they're only marginally engaging the threads.

If the hanger screws doesn't interfere with the skewer seat you might get away with a crude fix - buy longer screws and then use nuts on the outside of the hanger to hold it in place.

Thanks to all. The new hanger did the trick. Apparently the first third of threading of the old hanger was damaged, hence the Allen bolt could never catch the threading.

The mechanic added a bit of Loctite to the new hanger. It feels good to have a bike that's mechanically sound.