UKC

Hi,

Whenever I apply extra pressure to my pedals the chain slips, this was particularly embarrassing when pulling out onto a roundabout yesterday and I ended up on my arse. Like I say, it's not common, just when I exert more force than normal.

Do I need a new chain? Or is there more of a problem?

Thanks, Tony

Edit: This is on my otherwise very trusty Kona hybrid that I use for my daily commute in all weathers.

In reply to Tony the Blade:

A new chain may help, but are you sure it is slipping? When the teeth on sprockets and chainrings wear down they can either become more sloped, in which case the chain slips over them under tension - or more often they become hooked, in which case under pressure the chain temporarily gets hung up on the last tooth as the cog rotates and suddenly releases with a jolt that may feel like the chain is slipping. Either way you probably need a new chain and cassette, possibly chainrings too.

One other thing that causes a similar problem (and lead to a broken collar bone on my part) is to check that the arm on the rear mech maintains chain tension properly, i.e. that neither pivot point is seized.

In reply to Tony the Blade:


Wrong gear?

In reply to LastBoyScout:


That was my first thought - until it happened again

In reply to EddInaBox:

Ok, thanks for that. So I need to have a look at the cassette and rings as well, for rounded teeth?

I've had it about five years and it's done a fair few miles with minimal maintenance, so I guess it owes me nowt.

Cheers, Tony

In reply to Tony the Blade:

New chain and cassette. New chain rings could be required as EddInaBox said, but give the whole drive train and gear system a good clean and lube.

In reply to mrconners:

Message received and understood

Thanks

In reply to Tony the Blade:


If it looks like this, it is probably slipping:
http://www.unc.edu/~cupery/pics/bike_parts/IMG_1534--Campy_30t_chainring_wo...

If it looks like this, it is probably catching:
http://i35.tinypic.com/25hptme.jpg

Teeth should be symmetrical, compare the leading edge of the tooth with the trailing edge to see how worn they are, although be aware that some teeth on a cog are oddly shaped in the first place in order to help with smoother shifting. If there are some rings or sprockets that you seldom use they will be much less worn so you can get a better idea of what they originally looked like.

In reply to Tony the Blade:
Old chain was stretched so I put a new chain on last week.
It was skipping under load on smaller sprockets and small chain ring.
No problem in large chain ring when derailleur had chain under a bit more tension.

Cassette looked worn so changed cassette - no improvement.

Fiddled with rear derailleur - no improvement

Looked at brand new chain and found a couple of stiff links.
Each evening for a few days faffed about with chain tool to loosen stiff links.
Still no improvement. Kept finding stiff links.

Gave up and replaced brand new chain with another brand new chain.
It now works as near to perfectly as anything will on my bike.

TL;DNR
Check for stiff links even on a new chain.
If you replace cassette don't throw old one away for a few days as it may not have been the cassette.

In reply to Tony the Blade:

Its really worthwhile to check the chain (for stretch) fairly regularly using a chain checker tool (Park one prob best but about £17). In this way you can change the chain (fairly cheap) before it has worn too much and worn down the cassette and / or chain rings (much more expensive).
It sounds like you may have to replace these components now - but try with just a new chain at first. If it slips even more then you will have to replace cassette and chain rings.
Cheers
Steve

In reply to steveb2006:

Thank Steve - and others.

Having just ridden home I now note that it only happens when under load on the centre chain ring.

I'll go and look again at the state of the rings using EddInaBox's pictures.

Cheers chaps

In reply to Tony the Blade:

all of what Eddin a box says assuming its cassette and derailleur on the back,
and adding that it may be the block itsself starting to slip. the paws can fail inside, but if happening on center ring [ the one getting the hammer] likely not to be this ------------ you have some oil and no rust on the set?

In reply to Tony the Blade:

As said above - get a chain wear checking tool - for occasional use any one will do - I paid about £6 for mine. It should be fairly obvious if the cassette is worn as there will be a visible difference between the gears you use the most on your commute and those that you don't. Chances are that it's the middle range that is worn the most, which is where it skips. Blindfolded diagnosis is worn chain and cassette. I reckon to change them on the basis of two chains to one cassette, but only if you change the chain before it's totally worn. It's also worth checking that the derailleur is actually properly aligned with the skipping gears

To change a cassette, you'll need the fancy nut thing that slots into it (about £8) and a big adjustable spanner to hold the nut. You'll also need a chain whip. Or make your own by fixing a length of your old chain to a length of wood or thinking things through carefully with a length of the old chain and a vice.

In reply to steveb2006:


One lesson I learnt is not to buy the cheapo brand X chain wear checker. I did and thought I was being really good when I bought a new chain having got to the got to the 0.75% level where it is recommended to change a chain.
Unfortunately, after fitting the new chain and having problems I took the old chain to the LBS and using two different branded tools they told me the chain was actually much more heavily worn than my checker had suggested.