why does my chain skip to a different gear?

thehamo

Hi all,

Wondering if anyone can help me. Im not that technicall minded when it comes to bikes so I was wondering if anyone could diagnose my problem.

Everytime I try and accelerate, say at a traffic light, my chain skips of the cog and changes to a different gear, nearly sending me flying very time. It seems to be whn ever i put an preassure on t he peddals, like when im standing up going up a hill or something, again, chain skips and slips to a different gear.

Can anyone tell me why this is happening so I have some knowledge as to what needs to be fixed?

Thanks!

Lumen

This first.

sibyrne

thehamo wrote: »

Hi all,

Wondering if anyone can help me. Im not that technicall minded when it comes to bikes so I was wondering if anyone could diagnose my problem.

Everytime I try and accelerate, say at a traffic light, my chain skips of the cog and changes to a different gear, nearly sending me flying very time. It seems to be whn ever i put an preassure on t he peddals, like when im standing up going up a hill or something, again, chain skips and slips to a different gear.

Can anyone tell me why this is happening so I have some knowledge as to what needs to be fixed?

Thanks!

Gear may not be Indexed correctly. Due to cable stretch or slipping

Chain could be worn out.

How much mileage is on the bike?

Chips Lovell

And a skipping chain is also a sign of your needing a new one.

blorg

el tonto wrote: »

And a skipping chain is also a sign of your needing a new one.

Generally if the chain is worn to the point of skipping you will also need a new rear cassette, simply replace the chain on its own and it will continue to skip.

You can measure chain wear with a standard 12" ruler.

Generally worn chains tend to skip in place though so if it moves to another gear could be derailleur adjustment as Lumen suggests either.

thehamo

there is a fair bit of milage on the bike I would imagine. I bought it second hand, its a good bike but needed a few things doing to it. I suppose there would be no harm in getting a new chain on the bike anyway, and fingers crossed that works?

blorg

thehamo wrote: »

there is a fair bit of milage on the bike I would imagine. I bought it second hand, its a good bike but needed a few things doing to it. I suppose there would be no harm in getting a new chain on the bike anyway, and fingers crossed that works?

You could, but you will almost certainly also need a new rear cassette. The old chain will have worn the current cassette first before it started skipping. Bike shop should be able to advise. Measure the chain yourself if you want confirmation. Note you do NOT have to change the cassette every time if you change the chain before it wears too much- but if you are at the point of skipping it is likely too late.

Or it could be the derailleur.

MadHatter

thehamo wrote: »

there is a fair bit of milage on the bike I would imagine. I bought it second hand, its a good bike but needed a few things doing to it. I suppose there would be no harm in getting a new chain on the bike anyway, and fingers crossed that works?

If it has a lot of mileage, you may need chainrings too. Had that problem on my commuter when I put on a new chain and cassette, new chain skipped on old chainrings.

Quigs Snr

Possible causes.

1. Gear limit screws on rear derailleur require adjustment

2. Rear shift cable sticking (initially thought this could only cause poor shifting, not chain skip, till it happened to me recently).

3. Chain or Cassette worn out, could be one of both. Most likely chain. Try the chain first to see if it makes an improvement, if its not instantly better get a cassette too.

4. Everything could be absolutely fine, but you might have a stiff link in the chain. Flex each link, it should move freely, if one doesn't, then it could be your problem. Also check that the chain is not falling apart. I had one shifting by itself because one of the links was coming apart and hanging by a thread.

5. Are you sure its the correct chain for your drivetrain. Fixed up a secondhand bike for someone recently who had a 10 speed campag chain on a 9 speed dura ace drivetrain. Needless to say the result was not pleasant.

6. Less likely but possible is front chainrings, usually this would cause slippage but not involuntary gear shifts. Check for a shark fin pattern on the teeth (i.e. more worn on one side of the tooth than the other, not symmetrical.

7. Jockey wheel in the rear derailleur could be broken, offline or sticking or its spring return damaged (less likely).

8. Last but not least and the most common cause of bad gear shifting in race bikes... a bent rear mech hanger. Usually from the bike falling onto its drive side, even a small fall can bend the metal of the mech hangar slightly and make it damn near impossible to get the gears right. Learned this the hard way on the RAS after one of the team fell over in the carpark waiting for the start of the stage but thankfully the Rapha Condor mechanic had a vice in his van to straighten one for me. He spent quite some time giving out about people bringing spare 7000 euro bikes but not a 10 euro mech hanger without which the entire bike is worthless. Often you can pull the hanger back straight with your hand. But not always.

sibyrne

blorg wrote: »

You could, but you will almost certainly also need a new rear cassette. The old chain will have worn the current cassette first before it started skipping. Bike shop should be able to advise. Measure the chain yourself if you want confirmation. Note you do NOT have to change the cassette every time if you change the chain before it wears too much- but if you are at the point of skipping it is likely too late.

Or it could be the derailleur.

Very good point