Gears - 'hunting'

[Nebulous]

I've been having problems with my rear gear change for a few weeks. I've changed the cassette and the chain and have a new chainset ready to put in. I haven't changed all those entirely because of the problem, though I might have brought them forward slightly!

Anyway it's getting worse to the point that I did an event yesterday with a lot of climbing, and the bike wouldn't stay in one gear. Under load it would change up, and then a few seconds later change back down again. Next step is to change the cable- though I am wondering if the rear mech / hanger is out of true. Any thoughts on causes? Does the cable seem a likely culprit?

 

[Rob3rt]

Have you tried to re-index the rear mech? It could be cable stretch meaning the mech is not pulled across quite far enough leaving it sort of inbetween gears. You could increase cable tension to see if it resolves, if not try re-indexing from scratch.

 

[Globalti]

Change the cable outer where it curves around to the rear derailleur. They wear out and get clogged with dirt and rust and cause ghost changes, you need to change it every six months to maintain best performance. While you're at it, treat the bike to a new inner cable or at least clean the old one by pulling it through wire wool then lube lightly with chain lube.

 

[accountantpete]

As both the above have said.

If the cable is old then new inners and outers wouldn't come amiss. Make sure that all the outer cabling runs smoothly and is not too long and make sure that the ends of the outer cabling are cut flush. I pop ferrules on each end of each segment just to firm up the contact area.

 

[MontyVeda]

Change the cable outer where it curves around to the rear derailleur. They wear out and get clogged with dirt and rust and cause ghost changes, you need to change it every six months to maintain best performance. While you're at it, treat the bike to a new inner cable or at least clean the old one by pulling it through wire wool then lube lightly with chain lube.

every six months! Crickey mine was on for over a decade with no indexing issues before i changed it, and that was only for a new colour.

 

[Globalti]

That was on my mountain bike with frequent soakings in gritty Lancashire mud. I change the cable outer on the roadie almost as often.

 

[Nebulous]

Thanks guys - I think! I've been away today marshalling at youth crit races, and a very enjoyable day it was as well. We had a 10 year old lapping at 19 miles per hour!

What follows is entirely my own fault.
Cables were last changed at Christmas so it had to be worth a go. Edinburgh bike didn't have any, but Halfords had a Clarks set, so I set to, trying to change them before it became dark. On removing the cable the rear bend seemed fine, but there was something seriously weird going on where the ferrule joined the downtube barrel adjuster. It was very stiff, and the cable would barely move. Some metal on metal corrosion was going on, and the ferrule wouldn't budge. I must have missed greasing it when installing the last set of cables. Anyway a pliers on the ferrule, and another on the barrel adjuster, much huffing and puffing, and all I had was some seriously mashed metal. Very little chance of it going back in the downtube, and even less of getting a wire through it. I tried sticking the ferrule straight in the guide on the downtube, but it is too slack and wil bend the cable quite quickly.

So everything else is ready, cables all cut, front derailleur cable installed- but I need a new barrel adjuster. Any ideas on where to source one?

cheers.

Edit - I'll start a new more appropriate thread.

 

[Globalti]

This proves the value of regular maintenance, especially if you ride in wet conditions a lot, which I guess you do in Aberdeen!

The adjuster barrel is the kind of thing you'll find in a box of bits at the back of any bike shop so the best thing would be to go round your LBSs and ask nicely. I bet someone on here will let you have one if you post on "wanted". Otherwise a Shimano distributor should be able to get you one as a spare.

 

[Peteaud]

every six months! Crickey mine was on for over a decade with no indexing issues before i changed it, and that was only for a new colour.

You Tart

(ive been thinking of changing mine to blue )

 

[Nebulous]

Well I've got it fixed now - though not as easily as I hoped. Got the barrel adjuster fitted, fitted a new chainset, put the whole lot together and the gears were still changing up and down. Basically the only thing not changed on the whole drive train was the rear mech. I gave it a good onceover and the top jockey wheel did not seem parallel to the cogs on the cassette. The hanger looked ok, but the mech appeared to be twisted. It may have taken a knock at some time. I went for the brute force option, fitted a molegrip to the top of the cage and twisted. I've been out this morning and done 38 miles and its changing perfectly.

A standard 52/39 chainset is going to take a bit of getting used to after my 50/36 though!

 

[Globalti]

More than likely you bent the hanger and have now bent it back into approximate alignment. Derailleurs will not bend but hangers are designed to be the weak link like a fuse in a circuit so that they will bend or snap, protecting the derailleur. They are deliberately made from a very coarse low-grade alloy, something similar to what die-cast toy cars are made from, so that they will break easily. Once you have bent and re-bent a derialleur hanger you will have work-hardened it and seriously weakened it and can expect it to snap very soon.

You'd be well advised to go to the bike shop now and ask them to order a new hanger; it will cost about £20 but you'll be glad you've got it in your saddle bag when it snaps out on the road.

 

[Hawk]

I'd put a new hanger on for sure - mechs coming off your frame tend to end up in your spokes and have caused me superficial (mostly paintwork) damage to my frame also

 

[Globalti]

Yes, on second thoughts change the hanger; you do NOT want your derailleur going into the spokes, the result is usually catastrophic and expensive. Ask my son how he knows....