Gears jumping - help!

[Danny]

During my ride last weekend, my rear gears suddenly started jumping - i.e. moving up or down a gear. It seems to happen more on the larger cogs than the smaller cogs, but there is no obvious pattern at the moment.

My chain and nine speed cassette have done less than 2000 miles and don't appear to be worn. My Deore rear changer is the same age and is in very good condition. There is no obvious slack in the gear cable, no does it appear to be snagging on anything.

Any ideas of what I do next?

 

[accountantpete]

I'd try lubricating the inner cabling with oil as it sounds like it could be sticking at some point-usually a sharp bend.

 

[al78]

During my ride last weekend, my rear gears suddenly started jumping - i.e. moving up or down a gear. It seems to happen more on the larger cogs than the smaller cogs, but there is no obvious pattern at the moment.

My chain and nine speed cassette have done less than 2000 miles and don't appear to be worn. My Deore rear changer is the same age and is in very good condition. There is no obvious slack in the gear cable, no does it appear to be snagging on anything.

Any ideas of what I do next?

Check your inner cable. It could be that it has started to get a little corroded which will increase the friction with the outer cable.

I had a similar problem recently in that my gears went out of adjustment and I couldn't get them re-adjusted. Upon inspecting the inner cable I found that it was badly frayed where it is inside the shifter and that half the strands had snapped. Replacing the inner cable cured the problem.

 

[Mr Pig]

Agree with both poster above. I've had exactly the same symptoms, tried everything to sort it and turned out to be a sticky cable.

Remove the chain, then move the rear dérailleur in and out with the shifter. Look down on it. It should line up with the gears at all times. If it does not move back to where it was before but sticks between gears it's probably the cable.

New cable is not expensive but take your old outer cable to the shop so that they can cut the new ones to the right size.

 

[Danny]

OK, things got a lot worse today...

Checked the gear cable for any obvious wear, lubricated everything copiously, and set out for a ride. The gears felt like they were slipping as before*, and then after a couple of miles the whole drive train seized up and I discovered that one of the links on the chain had come apart.

Thinking maybe that I had failed to spot a broken link all along and this was the cause of the problems, I walked home 3 miles, changed my chain, and set out again. Straight away the new chain started slipping in the same way*, then it seemed to be getting better, but after 8 miles I had a couple of big chain slips and the new chain came apart throwing the dérailleur into the rear wheel, and me onto the grass verge.

* On my second ride I was trying to work out exactly what was happening with the chain, and realise that the description in my OP was wrong. The chain isn't jumping gears but slipping periodically on whatever cog it happens to be on. There doesn't seem to be any obvious pattern to when it slips - sometimes it will slip after 2 or 3 revolutions of the pedals, and then go for half a minute or more without slipping.



PS And to top thing off, when I got eventually got home I found my rear tyre had been punctured by such a massive thorn that I had to dig it out with a penknife.

 

[Mr Pig]

Sounds like a new chain on really worn gears.

 

[Danny]

Gears have done less that 2000 miles, and the first chain that broke was not worn.

 

[Danny]

Have added Chain No.3 and it still seems to be slipping in the same way. Any ideas?

 

[accountantpete]

Have you a rear sprocket that you seldom use? If so try the new chain on that sprocket -if there is no slippage then the cassettes nackered.If it still slips then it's a new cassette and chainring by the sound of it.