Gear(s) skipping on newish bike

[DaveReading]

A couple of weeks ago I started to have a problem with one of the gears on my rear mech skipping momentarily to a lower gear (bigger) cog and back again.

I tried the usual things - cleaning and re-lubing the chain and front/rear rings, and re-indexing. On the stand, and on the road, shifts are very smooth, up and down, and it's only under load that the skipping occurs.

Bike has only done about 500 miles, and there are no obvious signs of wear on the rings or chain, except for evidence of rubbing on the side faces (not the teeth) of some of the rear cogs, which may or may not be normal.

Cassette is a Shimano HG31 11-32 8-speed, chain is an HG50. I'd rather learn how to fix this myself than take the bike to the LBS, and I don't mind spending a bit of money on it as I expect to keep it for a while. Would it be worth replacing the chain and cassette (in which case I might opt for an 11-34)? If not that, what else could be causing the problem?

 

[TheDoctor]

With only 500 miles it's unlikely to be chain or cassette wear - cable stretch would be my guess.
I'd re-index the gears. Also, is it just skipping in one gear? If so, check there's nothing glaringly obvious on that sprocket (like a missing or bent tooth) and then tweak the indexing to smoothen out the shifts to / from that sprocket.

 

[mrandmrspoves]

I agree with TheDoc - but cable stretch would normally cause the gears to change to a higher gear rather than a lower gear. If you are correct and the gear is moving to a lower gear then I would try loosening the cable a fraction rather than tightening it. If it works great - if not, start from scratch and index the gears again. (Look up how to do it on YouTube) It is really simple - but if you are indexing your gears I would always advise re-lubing the cable too.

 

[DaveReading]

Thanks, chaps. Yes, I can see how backing off the cable tension slightly would lessen the tendency to skip into a higher gear, though I'm worried that might in turn affect the rest of the shifting - but it's worth a try. I'll lube the cable again too.

If that doesn't work, I'm still tempted to replace the cassette (with a slightly wider range) and chain, unless there is anything else worth checking out first.

 

[mrandmrspoves]

One other thought is if you have a replaceable gear hanger make sure it hasn't worked slightly loose....and if there is any chance that the gear hanger has been bent that should be replaced.

 

[bozmandb9]

Sounds a little crazy to me thinking of swapping out parts to fix an issue on a new bike. How long have you had it?

I had an identical issue with my bike from new. It turned out there was a little carbon fibre in the frame interfering with the internal cable routing. Even after it was removed, the issue didn't resolve until cable was replaced.

Did have a few issues with gear hanger too!

 

[Rob3rt]

Probably just missing a cable tie or 2....

 

[DaveReading]

Thanks. Cables aren't routed internally, so I think I can rule that out.

Yes, the bike is only 15 months old, so I hadn't been thinking about replacing anything until the problem started a couple of weeks ago.

Anyway, as well as checking and lubing the cable, and ensuring that the hanger is straight, I've ordered a lockring tool and chain whip so that I can remove the cassette and take a closer look at it - can't do any harm.

 

[bozmandb9]

I guess 15 months isn't quite new, but would hopefully still be under warranty. Personally I'd be wanting the shop where I bought it to sort it out. Does it only skip once or twice, or does it sort of oscillate between the two cogs? That's what mine was doing. Also is it every time, or intermittent?

Another thing they found on my bike was that the cassette was not fully tight, that is certainly worth checking.

 

[SquareDaff]

I had something similar a while back and the problem was the clear plastic "throw off" disk on the back wheel. In my case one of the nobbles had worked snapped off causing the disk to warp and put pressure on one side of the cassette meaning it "wobbled" whilst riding. Can be seen by spinning the wheel and seeing if the cassette stays stable on the axle. Solution- remove/replace the piece of plastic.

 

[Globalti]

15 months old and you still haven't replaced the cable outer at the rear derailleur? That's your problem. The cable outer wears and gets crudded up with dirt and rust causing exactly the symptoms you describe. Get the bike shop to cut you several lengths and buy a couple of inner cables and some cable end ferrules and inner cable caps. Fit new and you'll be amazed at how much deterioration in performance you've come to accept as normal.

 

[DaveReading]

Update:

Having tried all the above and got my changes smooth as silk, I went for a 25-miler round Oxfordshire yesterday with the boss and still encountered the skipping problem.

So this morning I used my newly-acquired chain whip and lockring tool to remove the cassette for examination. Having looked at the removal operation on YouTube, I was prepared to have to use a bit of welly - but the lockring came off with virtually no torque at all.

Inspected the cassette, which showed little sign of wear and no evidence of teeth out of true, gave it a good cleanup, then replaced it and tightened the lockring using my carefully-calibrated arm to what seemed a reasonable torque (I have a torque wrench, but alas no socket that fits the lockring tool).

First signs are good, a quick belt round the block evidenced no skipping, but the proof of the pudding will be a long ride with some hills.

Could the fact that the lockring wasn't very tight when I removed it have been causing my problem? I know a freehub isn't like a freewheel, which tends to tighten with use - could the lockring has loosened slightly after a year of problem-free riding?

Either way, if a longer ride shows no recurrence of the skipping gears, I'm not going to look a gift horse in the mouth. But it's been an educational few weeks.

 

[byegad]

Could be, I had one locking ring come clean off and the thing hunted up and down gears all of the time.

 

[PpPete]

Not experienced it myself although Mrs PpP's bike was skipping about the gears a while back and we found play in the outer sprockets - due to loose lockring. Tightening that seemd to cure the problem.
The only time I've had a lockring come loose it jammed the entire drive train.