Lowest gears Slipping

[HLaB]

My bike has only done 263 miles but I'm finding the lowest 2 gears are slipping (the 38x25 and 38x24) on the cassette everything else seems fine (including the 52x24). Has anybody any ideas what the problem is? things may just need tightening. I don't really want to take back to the not so local lbs 50 miles away. The first time I can get to it is Sat the 15th.

 

[Ceedee]

My bike has only done 263 miles but I'm finding the lowest 2 gears are slipping (the 38x25 and 38x24) on the cassette everything else seems fine (including the 52x24). Has anybody any ideas what the problem is? things may just need tightening. I don't really want to take back to the not so local lbs 50 miles away. The first time I can get to it is Sat the 15th.

Have you tried the cable tension on the rear derailier? maybe your cable has stetched slightly.

 

[Radius]

Have you tried the cable tension on the rear derailier? maybe your cable has stetched slightly.

This.

 

[Browser]

More information required please. Is the rear deraillieur shifting up cleanly? Are you getting the normal clatter of a mis-aligned rear D. when those two gears are selected? By 'slip', do you mean the chain slides freely around the casette or rather does it jump every few cm of chain travel? Is the front deraillieur set up OK?

 

[HLaB]

Now I've had it up in the workstand I can see whats going on, when the bottom two gears were selected the chain was riding up on top of the sprockets rather than interlocking. I'm guessing the mis-aligned rear derailleur was the issue. I've tightened the b screw and it seems to be interlocking correctly; I'll find out tomorrow when I take it for a test ride.