Chain Slipping

anton1r

Hi all,

Looking for some advice on a drivetrain issue. A while ago the missus was complaining about having some gear trouble so I had a fettle tried reindexing but I couldn't quite get them sorted. So I had a decent look decided her chain/cassette/rear mech cable looked a bit past it so I replaced those. (While I was at it I broke the freehub but I've since replaced that).

Anyway, I sort her out with a new cassette, chain and rear mech cable, index the gears in the stand, give it a quick pootle and declare jobs a good un. Until I rode it to work...

If I put any power down on the pedals the chain skips (I cant quite work out where) it's most annoying so I put the bike back in the stand. Hmm... chain looks a bit saggy, I can't see why that's the case or why the slipping, any advice?

Attached some photos...
Chain sag


Jockey Wheel


Chain Set


Any advice would be more than welcome!

Cheers (Apologies for the long post!)

cooldad

Chain is way too long, measure it around the big/big rings (not around the mech) plus a full link.

cooldad

Althouh looking at it again, the mech looks fubared.

anton1r

Hey,

I didnt think a new chain would need links taking out but maybe you're right, its an HG40 on an 8 speed bike?
http://www.edinburghbicycle.com/products/shimano-hyperglide-chain-hg40
I have thought the rear mech looks odd but it shifts well enough in the stand, surely if it was borked it wouldn't shift?

Actually should the cage of the mech not be pointing backwards a bit rather than straight down?!
Cheers for your help.

pdw

You will need to shorten a new chain, but I don't think that sag is caused by chain length - the problem is the rear mech. As you say, the lower arm of the mech and lower jockey wheel should spring backwards to take up the slack. It's got plenty of travel to do so, so either the spring is completely broken, or it's just seized up.

Try moving the lower arm of the mech whilst holding the top part steady and you should be able to tell whether it's just gummed up, or broken. If it's the former try flushing it with WD40 and seem if you can free it up. Otherwise, new mech time.

The lack of tension in the chain might well be the cause of the chain slipping. If not, next suspect would be worn chainrings, although the large one in the photo looks OK.

anton1r

Nice one pdw, the rear mech being the issue kind of makes sense as even with the old chain on it had a sag like this.

By lower arm, which bit do you mean? The cage with the jockey wheel or the bit that says Acera on it or the other silver bit in the middle?

Cheers.

anton1r

Looks like i've got this solved guys, it's the rear mech as cooldad and pdw suggested.

Thanks.