Bob Ross

I was in a nasty crash yesterday, but I'm clearly beat up more than the bike is. The only non-cosmetic damage is that now when I shift into the largest cog the rear derailleur cage is rubbing against the spokes.

I'm just trying to get an idea of whether that could be a symptom of something other than a bent derailleur hanger?

i.e., is it possible for the derailleur itself to somehow get bent? Or, for the rear wheel to somehow have gotten re-dished due to impact? Part of me thinks those seem really unlikely...and part of me wonders if those are common occurrences, or if there are many other common occurrences that I haven't even considered.

It's more of an intellectual exercise/learning experience, because no matter what the answer is I'm still gonna just bring it to the LBS and say "here, please fix it." But I'd like to understand the mechanism of the problem just for my own edification.

Thanks.

cny-bikeman

I believe there are better ways to exercise your intellect, but here goes: Observe how the derailleur moves and articulates. Can you conceive a scenario where it could bend on its own in such a way as to get closer to the spokes? If you can, how would your fall have created those conditions? Do the same for your wheel - how could the wheel have been re-dished by the fall, and how could that put the derailleur close enough to rub the spokes?

Now for the part that takes only simple observation. Put the chain on the large chainwheel and small rear cog, and view the derailleur from the back of the bike forward. What part is bent?

Intellectual exercise is best preceded by observation, so as to limit what possibilities are considered.

dsbrantjr

First rule of troubleshooting: Fix what you know is wrong before proceeding.

zacster

Sounds like a bent derailleur hanger to me. It is a relatively easy fix if you have the tool. Bring the bike to a shop if you don't want to buy one. I bought one because I have 7 bikes, and at least 4 of them had bent hangers, and the other 3 were new.

fietsbob

So, as said above, step numero uno, check the RD hanger alignment..

when the shop has done the work you can ask them to demonstrate what they needed to do..








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MobiBike

Bent derailleur hanger is the most likely problem.
Once the derailleur itself gets bent, it will never shift right again, but this is the more rare problem of the 2, but can happen. (it has give because it is already designed to move)

Step 1 is Fix the hanger, it needs the tool to get it right, but in a pinch (emergency get home tactic because you can over do it and break aluminum hangers kinda easy) you can pull it back out with some care, by shifting to the small cog, pull gently and firmly on the body (not the pulley cage) until it gives just a little. Then check to see if it stops shifting into the spokes, and doesn't shift off between that small cog and the frame.

Step 2 after the hanger is straight, check for proper shift indexing, unless you have friction shifting in which case you can just use it.

The wheel would not become "re-dished" without you noticing it got bent, as in bent good first and you noticed the spokes pulling through the rim every other one.

Aubergine 

I concur that it is most likely a bent hanger, but I have seen bent derailleurs as well. You just need to eyeball it to see which one (or both) is bent.

I have realigned several bent hangers using an adjustable wrench. An alignment tool is nice to have (our co-op does have one) but not strictly needed to get things running smoothly again.

SkyDog75

The derailleur hanger is designed to be a sacrificial part, meaning it's supposed to give way before the frame (and hopefully the derailleur) do. And that's usually how things work out. So start by aligning the hanger. Once you do that, check to see if the derailleur's cage is parallel with the cassette cogs. If so, it's probably good.

Kontact

I doubt that changing the dish would allow spokes close to the hub to change location that much.

You could wack a derailleur hard enough in to the stop screw to change the setting, but completely unlikely.

Small hanger bends are hard to see.

MobiBike

So Bob, hopefully you gleaned enough here to know how to proceed next. But I am wondering how the rider is repairing now? It sounds like you took it harder than the bike.

Bob Ross

Unfortunately this is not a discrete hanger, it's part of the rear dropout. (TIG-welded steel frame) Presumably it can still be bent back into its original aligned position?


Thanks. Lots of road rash and some fascinatingly colorful bruises and hematomas, painful to touch (which makes sleeping difficult) but nothing to keep me from living life full swing. Including a short bike ride -- on a different bike -- yesterday.

Koyote

Sure, it can probably be bent back. A shop can do it in about ten minutes with the correct tool.

The problem with the integral hangar is that you can't fix it an unlimited number of times. But I have an old steel frame on which the integral hangar has been bent back into shape 2-3x, and it hasn't broken yet. (Fingers crossed.)

aggiegrads

The good new is that it should not break JRA (just riding along). The hangar does not see high amounts of stress in normal use, so only forces that cause plastic strain should cause a low-cycle fatigue failure. These forces should only be encountered while the hangar is bending, so if it survives the crash and realignment, you should be fine until the next "event".

Koyote

Oh, yeah, I know, but that is good clarification for the OP.

I'm just trying real hard to not crash and bend the hangar again.

MobiBike

A steel frame hanger can be bent back usually several times depending how bad it was bent,.. kinda like a steel paper clip. Aluminum bikes really have to have a replaceable hanger, because it will break really easily (it is for this reason they were invented so the industry could also hide this fatal to the frame flaw of which many had 2-5 year warranty as opposed to lifetime on steel bikes). This is one reason I rarely buy or use aluminum bikes... I've seen too many failures of multiple kinds to trust used ones of which I do not know the history. Steel will "tell" you before it breaks most of the time.

For you... High quality Vitamin C with bioflavonoids (non-gmo!) taken in higher amounts has been shown to aid in the speedy healing of blood vessels and skin repair, along with a host of other great things, I have found in my own personal use for such things.

Homebrew01

Yes. It should be able to be bent back.

Next time, crash on the non-drive side ...

San Rensho 

Stop. Don't ride the bicycle. If the rear derailleur is bent and into the spokes the next thing is going to happen is you shift and the derailleur is going to get caught in the spokes and twist it off and you will be in a world of hurt, because now you've ruined the derailleur and it can also jam and cause a crash.

zacster

Oh please, stop being so dramatic. Just adjust your limit screw so it doesn't hit the spokes until you get this sorted out. I've ridden a bike for years that hit the spokes without any problems.

Koyote

I would go with San Rensho's advice on this. A friend crashed and bent his hanger, then tried riding the bike again - just to check whether it worked. Ended up with a trashed RD, trashed rear wheel, and had to send his custom steel frame back to the builder to have a new derailleur hanger welded on - which necessitated fresh paint. It was expensive.

Having a shop deal with it is cheap, and safe.

rumrunn6

further proof of the value of n+1. & as they say in fishing, you lose one, you rig one

https://www.tzr.io/yarn-clip/d7b61e7e...6-9fd08ebea65e

davidad

You can straighten the hanger easily if you don't have the tool, but have a spare rear wheel. The rear axle of most wheels is the same bolt size as the rear der. hanger. Remove the der. and thread the spare wheel on the hanger and use it to bend the hanger so that the two wheels are parallel.
Poor boys repair that works.