chain slipping in middle of block

[Zippy]

This is on a brand new road bike after four week's commuting. The chain is slipping in mid range gears; seems ok on easiest and hardest cogs.

I wonder if it is due to cable stretch and indexing needs tweaking. It is nealy due to go to lbs for its free six week maintenance so maybe I get it in early in case I have damaged anything in slipping under pressure once or twice.

It was scary first time it happened as I had become settled with its ways; suddenly slipped with a crunch as the chain left one cog for the next one down - uphill in traffic!

 

[Smokin Joe]

Yes, the initial stretch in the cable has put the indexing out.

There is a good video on youtube which explains how to do it. Forget the bit about limit screws, wait for the indexing adjustment.


View: http://www.youtube.com/watch?v=SjJfKO_tAo0&playnext=1&list=PLCFAD2D2BBA98A250&index=2

 

[Tynan]

small chance that's it some crap in the cassette, had that once, some plastic bag had got in there and wound itself in very deep while camouflaging itself with grease

 

[Gerry Attrick]

When it slips, does the gear change to the next higher one? If so try lubricating the cable guide under the bottom bracket.

 

[Zippy]

Hi - it slips down which, being a brand new bike and therefore a brand new gear cable, would suggest the cable has stretched putting the indexing out.

I will have a look at leaving the limiting screws alone and tightening the cable tensioner barrel.

 

[Gerry Attrick]

Before you alter anything, try doing as I suggested, lubricate the cable guide under the bottom bracket. What happens is that frame flex during hard pedalling can cause the guide to grip the cable resulting in an unwanted change to a smaller sprocket.