Rear mech knocked

[quixoticgeek]

My bike fell over the other day, knocking the rear mech. It didn't go into crash protection mode, and it still shifts, only now when i shift into 1st gear, it throws the chain over the block into the spokes. Is this because the derailure has been bent, or is it more likely the steel frame hanger is bent? How would I tell which is which?

What is the likely best way to fix this? I could just adjust the limit screws, and have it work in this position. Or I could take it off, and have bend the hanger into the right position.

What do people recommend?

J

[robgul]

Put the bike in highest gear (smallest sprocket on cassette) and look at the bike from behind - the mech jockey wheels should be algned under the sprocket and the derailleur cage vertical.

Damage may be the mech itself or the gear hanger bent (which may be fixable)  - I'd go to the LBS

Rob

[Kim]

If it's an integrated steel hanger, those bend (and bend back) fairly easily.  Best to straighten it, (there's a tool for bending and aligning mech hangers with reference to the rim, or you can improvise with another wheel) rather than mucking around with the mech, which may have unintended consequences.

If it's a replaceable alloy hanger, you can have a go at straightening it in a vice, but it's basically sacrificial.

[bludger]

I think it's most likely the hanger, rather than the derailleur - they are designed such that the hanger will bend to prevent derailleur damage. If the derailleur is damaged then it is highly likely that the hanger is fit for the bin IMO as it's probably badly weakened and liable to snap mid ride.

It is pretty difficult to eyeball check the alignment of a derailleur hanger. Ideally the best check is to swap the hanger with a spare hanger ordered from online, and check the performance but I appreciate you're probably not in a position to do that. Some bike shops will be able to bend the hanger back into shape using a special tool made by Park but it's impossible to do precisely by hand.

My choice would be to find a good bike shop and see if the hanger is in a re-bendable state, and in the meantime go online and order yourself a new mech hanger since you want one as a spare anyway. https://derailleurhangerstore.co.uk/pages/how-to-identify-your-derailleur-hanger is a site my mechanic recommends but I found with mine I could just google 'kona wheelhouse 2018 derailleur hanger' and it came up. The spare lives inside my frame bag in a repair kit.

[Tim Hall]

You can measure ( and correct) a wonky mech hanger in the absence of the appropriate special tool by screwing the spindle of a spare rear wheel into the mech mounting hole (remove the mech first) and measuring the gap between the two tyres/ wheels at 12, 3, 6 and 9 o'clock.  Lean on the spare wheel to adjust.

Or take it to the LBS as suggested upthread.

(Xpost with Kim)

[quixoticgeek]

It's an integrated steel hanger, in so far as it's part of the frame, not a separate bolt on hanger like on many ali or carbon frames.

Looks like I need to take a slow ride across the city to the LBS...

J

[bludger]

Hope they manage to cold set it OK

It's interesting to me how some steel frames have integrated hangers and others like mine opt for a detachable one. It might be to do with the tyes of steel - apparently mine (853) is a bit more of a pain to work with so perhaps that's why the designers opted for a swappable one.

[Cudzoziemiec]

There is a special tool for measuring derailleur hanger alignment, which your LBS might or might not have.

[Brucey]

I agree the hanger alignment needs checking.  If you adjust the stop screws in direct contradiction to the indexing, the system will 'fight the stop screw' to some extent and this will probably (sooner or later) cause 'something very bad' to happen.

cheers

[grams]

As it’s Di2, set it to a middle gear and unplug it for the trip to the bike shop.

this will probably (sooner or later) cause 'something very bad' to happen.

It’ll cause the motor to stall, and the software will stop trying to move it after a couple of seconds. Worst case scenario the crash protection link will pop open, although I don’t believe the motor has the torque to do this.

[quixoticgeek]

Got the bike up on the work stand at my LBS.

In this light you can really see the bend in the hanger.





My tame mechanic is setting it back into position.

J

[quixoticgeek]

All fixed!

J

[Cudzoziemiec]

 

[bludger]

Please post a photo of that cassette once you've been at it with the gt85 and pipe cleaners 😩

[Brucey]

its impossible to be sure from those photos (the fisheye distortion is terrible) but it kind of looks like the adaptor plate between the hanger and the mech is bent and so might the hanger still be too.  If so it might be a case of two wrongs making a right, which is quite workable with single-pivot mechs.

Did the hanger get checked for absolute alignment, i.e. vs the wheel?


cheers

[quixoticgeek]

its impossible to be sure from those photos (the fisheye distortion is terrible) but it kind of looks like the adaptor plate between the hanger and the mech is bent and so might the hanger still be too.  If so it might be a case of two wrongs making a right, which is quite workable with single-pivot mechs.

Did the hanger get checked for absolute alignment, i.e. vs the wheel?


cheers

Not absolute alignment, just getting it back to straight by eye.

The adaptor plate is an integral part of the rear mech, or rather it came with it. I think it's supposed to be removed when using direct mount, but I'm not sure. It doesn't look bent to the naked eye, I think it's just the distortion of my phone's camera.

J

[bludger]

Since we're on the subject I just took the crit bike into my trusted shop after persistent dodgy shifting despite my best efforts to index fettle.

Turns out the hanger was bent and the cassette lockring wasn't really tight enough. But also the actual shifting ratchet mechanism for the rear brifter is starting to show its age (it's a few years old, 10 speed campag Chorus). They did their best to put it in good condition but alas the gubbins may only have a few years left in it.

[Brucey]

Since we're on the subject I just took the crit bike into my trusted shop after persistent dodgy shifting despite my best efforts to index fettle.

Turns out the hanger was bent and the cassette lockring wasn't really tight enough. But also the actual shifting ratchet mechanism for the rear brifter is starting to show its age (it's a few years old, 10 speed campag Chorus). They did their best to put it in good condition but alas the gubbins may only have a few years left in it.

Gazing into my crystal ball, I see that G springs are in your future....

Probably.

If you can  still buy them that is....

cheers

[Oxford_Guy]

Since we're on the subject I just took the crit bike into my trusted shop after persistent dodgy shifting despite my best efforts to index fettle.

Turns out the hanger was bent and the cassette lockring wasn't really tight enough. But also the actual shifting ratchet mechanism for the rear brifter is starting to show its age (it's a few years old, 10 speed campag Chorus). They did their best to put it in good condition but alas the gubbins may only have a few years left in it.

Gazing into my crystal ball, I see that G springs are in your future....

Probably.

If you can  still buy them that is....

G-springs for 10-speed Campagnolo Ergos still seem to readily available, as well as most other Ergos spare parts

[Brucey]

last time I looked, G springs and G spring carriers were readily sourced, but index wheels were not.   

cheers

[Paul]

G Springs here:

http://www.gbcycles.co.uk/p/35964/Campagnolo-Ergo-Index-Spring?kw=&fl=1000&ci=44622668222&network=pla&gclid=EAIaIQobChMIxJ2BrLP94wIVCLDtCh1pQA6XEAQYASABEgJXifD_BwE (and elsewhere, for all I know)

Instructions for fitting here:

http://nuttycyclist.co.uk/cycling/ergo-rebuild.htm (also probably elsewhere too, but a sense of loyalty...)

[Paul H]

Another post to reinforce my belief in the advantages of dork discs, I know, I know,  they're not called that for nothing and the true sign of some POB who knows no better, but IMO it's nothing like a dorky as a wheel with half the spokes missing. 

[Kim]

Another post to reinforce my belief in the advantages of dork discs, I know, I know,  they're not called that for nothing and the true sign of some POB who knows no better, but IMO it's nothing like a dorky as a wheel with half the spokes missing.

If you had one of those mech protectors they fit to children's BSOs, the dork disc wouldn't be needed...

[Cudzoziemiec]

Those, um, dork cages look quite a neat idea to me. Or rather, not at all neat and they probably make adjusting the gearing more fiddly, but they'd fit in with a utilitarian hybrid around town type aesthetic.

[Kim]

Those, um, dork cages look quite a neat idea to me. Or rather, not at all neat and they probably make adjusting the gearing more fiddly, but they'd fit in with a utilitarian hybrid around town type aesthetic.

I had one on my folding BSO, because I kept bending the cheese on the door slalom of the entrance of our London flat.  Probably still got it in a box of bits somewhere.

Main problem was it reduced wheelbender compatibility.