Bicycle Mechanics - Adjust / tweak Rear Derailleur...

Hi,

I have just fitted a new Shimano 105 Rear Derailleur to my new second-hand bike (replacing an Ultegra unit that was damaged) and I can't quite adjust it correctly. I think I've successfully set the High and Low screws, and the cable tension, but it's not quite working properly.

I can set it up so that it seems to change up correctly (i.e. from small cog to large cog), but when I click it back down, it doesn't shift and stays on the largest cog - but it will move down with a second click. Even when I tweak it so that it seems to move from the largest to the second largest well enough with one click, it doesn't quite behave on the smaller cogs. It seems as though I've tried every possible combination (within reason), but I haven't quite got it yet. All the video tutorials on Youtube look so easy.

At times it seems as though it might be OK, but when I take the bike on the road for a spin it just doesn't operate smoothly.

Does anyone have any hints and tips for me? Anything I can try before I cave-in and take it to a bikeshop for a service?

Regards
Mick

Why was the old one damaged? is the hanger straight? have you followed the instructions the Shimano give you / the Park tech quide? Does the gear cable (inner/outers) need replacing?

Lots of possibilities, to look at, once you have eliminated things like the hanger, would start again, with the H/L screws in a neutral position, and give it another go.

Why was the old one damaged? is the hanger straight?

That's what I think too.

Bent derailleur hangers are common. A damaged derailleur makes me suspect a bent derailleur hanger and, the symptoms that you describe are frequently caused by a bent derailleur hanger. Shops have a tool for realigning hangers. It's only about a 10 minute job so it shouldn't cost too much.

Thanks for the reply - can a slightly bent hanger make that much difference?

Would a local bike shop have a replacement? As I know there are many types available.

Mick

Steel / Ti frames normally have built in hangers, these are not replaceable, but can be bent back, any good LBS should have the correct tool, normally from Park, but there are several other good manufactures of bike tools out there (VAR, Cyclus etc)

Alu / carbon frames normally have removable hangers, if you have this, would initially check that it is done up tightly, as this can introduce some wobble, for replacements; unless the bike is from a brand the shop sells, don't expect them to have it in stock, but any good LBS should be able to order one for any bike from third party suppliers (Wheels Manufacturing and others).

Thanks for the reply - can a slightly bent hanger make that much difference?Yes, absolutely. The behavior you describe is totally indicative of a bent hanger.

It is possible your hanger can be bent back into place even if it's a replaceable type. Often the replacements are not perfectly straight and require adjustment anyway. Same tool for all.

I'd agree with the bent hanger. Check out http://www.derailleurhanger.com for a replacement.

Thanks for the reply - can a slightly bent hanger make that much difference?

Yes and the more rear cogs you have the more difference it makes. I can "eyeball" a 7-speed drivetrain hanger and get perfect indexing. On a 9-speed, I definitely need a gauge to get the alignment precise enough.

Thanks for all of your replies! A bent hanger it is then!

It's a removable type, so remove it and bring it into the shop, or order one online if none has one.

It's quite a good bike, so it's worth sorting out properly.

Thanks so much - a very big help.

Thanks for all of your replies! A bent hanger it is then!

It's a removable type, so remove it and bring it into the shop, or order one online if none has one.

If it's not bent too badly, a shop might be able to straighten the one that you have but they'll need your whole bike to do it. You can almost surely get a replacement (I'd order 2) from derailleurhanger.com, but it might be necessary to align even a new hanger with a gauge.

Hi Guys, I've bent it by hand and it seems to be OK now - thanks for your advice. Hopefully it stays that wat!

Thanks again!