Skipping but only in some gears

[grhm]

I've got a couple of issues with my bike a the mo. First up, I'll admit to doing next to no maintenance over the winter. My bike is used for commuting 5 days a week and it's been dark at both ends of the day and I've been busy at weekends. (Excuses I know but ...)

I thought I was doing enough to keep my chain maintained, but one week it was fine on Monday and had gone orange with rust by Wednesday. I gave it a thorough clean and scrubbed most of the orange off and it's been ok-ish since.

However last week, something started making a god-awful clunking and clicking noise as I pedaled. Particularly if I was pedaling hard and/or out of the saddle.

I bought a new chain and replaced it at the weekend. I looked at the cogs - but none appear to be "shark-fin shaped" to my untrained eye so I decided not to replace them.

Having given everything a good clean before putting on the new chain the bike feels as good a new - almost.

It skips when I'm 3-4th gear at the back - possibly also 2nd, I'm not sure. (There are 8 at the back).

This only seems to happen when I'm pushing hard (usually when climbing but not always). This means I've not been able to see what going on myself - just hear the clink and feel the pedal jump (usually breaking my rhythm and hence making the hill so much harder!)

It seems to happen when I'm in either the middle or smaller chainring. Don't think I use 2-4 when in the largest chain ring (or if I do I'm pulling up to a stop).

Any suggestions on what I ought to be looking at and how to fix it? If I can't get it sorted myself, I'll take it into my LBS but I'm loath to as my wife has the car during the week and it's awkward without it or messes up both of us if she give's me a life after the shop is open.

 

[ChrisKH]

I have the same problem. Bike shop said there was a compatability issue between front and rear equipment (cogs/derailleur) being used which wouldn't sort itself out unless something was replaced. As it's virtually a new bike, this is a bit disconcerting. Not necessarily the problem with yours but worth a thought.

 

[grhm]

I'd hope not - I bought it new last autumn and would expect the parts to be compatible. I bought the chain from the same shop, whilst stood next to the bike, and was asked "Is it for that bike?" before being given an 8 speed chain.

It's a Giant CRS 3.0 (2008 Model) - but I doubt anyone need that info to suggest what might be wrong.

 

[gwhite]

First thing to do is to check for a stiff link. Raise the back wheel up and move the pedals backwards while watching the sprockets. If you have a stiff link you will see the chain jump as you do so. If you do have one, lube the link by grasping on either side of the link using a cloth, twist with both hands against each other until the link loosens. If this doesn't do the trick then you will need to loose the offending link with a chain tool.
If this is not the answer then you should look closely at the sprockets checking for wear. If your chain has been badly worn this can cause wear on the chain-rings and rear sprockets. If the sprockets are OK then check the tension of the rear der cable. Instructions can be found at Parktool repair help.

 

[snakehips]

I have eliminated this problem on a couple of bikes by replacing the freewheel (as it was on my bikes). Something was wrong with a couple of sprockets , not all , which is why the problem only occurs in some gears.

 

[HLaB]

I've got a similar problem I only really notice it on a club run when I guess things are under a bit more strain and although my cassette looks fine to me it mustn't be perfect and the extra strain highlights it. When I get a new chain that cassette will of had 2 or 3 chains and I'll replace it I'll live with it till then.

 

[palinurus]

The cassette has worn to match your old chain. Now you've changed the chain it jumps when it runs over the most worn sprockets. Some of the sprockets are less worn which is why some combinations work fine. A new cassette will probably fix it.

 

[Big John]

I agree totally with Palinurus. The sprockets you use most have worn. The new chain isn't meshing with the old block, hence the jump. Bite the bullet and get a new block while the chain's new. It's unlikely to be the chainrings. I've had the same chainset on my winter bike for years. They do wear eventually but not like the sprockets at the back.

 

[spence]

Also agree, change the cassette. The teeth on the rings tend to "shark fin" where the cassette tends to show wear as an extended "valley" between the teeth.

 

[grhm]

Hmm, replace the casette. That's what I thought would be the answer. I'll have a check for a stiff link and I'll check the old chain to see how worn it was - not sure if it had stretched much but it had seized up with rust.

The fact that it's doesn't do it all of the time (only happened once in 3 miles last night) and that it only does it in cogs 2-4, means in probably is wear - but I was hoping to get more than ~6mths/800miles out of a chain and more out of a cassette.

How often would you expect to change a chain and/or cassette on a daily commuter?

(Thinking about it cog 2-4 are probably the cogs I spend more time in, either climing or pootling in traffic. I can speed along in top gear and want the next gear - but it's nowhere near as frequent - or sustained)

 

[spence]

Yep, got a dozen or so old cassettes in the draw - why do we keep knackered kit?? - all with only half the cogs worn. Says something about not needing all these gears in the first place.

Usually get through a couple of sets (cassettes, chain and rings) on the HT in a year which is mainly used in the mud and sand around hear and one set on the full sus. Don't know about the road bike, only just brought it.

 

[HLaB]

I usually get about 1500 miles out of a chain before its 0.75% worn and replace the cassette every 2nd or 3rd chain but from reading earlier threads some folk get a lot more.