Rear Mech Slipping

steelo

I've just fitted a new chain and cassette to my MTB. I've adjusted the rear mech so the gears were changing sweetly in the dry conditions when out riding. However, last night it was ridiculously wet and muddy and the rear mech/chain was constantly jumping so it felt like every 2-3 pedal rotations the chain was slipping as though there were no teeth on the sprockets.

Is this a common thing to happen when the rear mech/chain gets muddy or is it an alignment issue?

I thought I had the rear mech dialled in nicely but after last night I'm doubting my abilities! Maybe I'm just out of touch with how a bike performs in the mud?

Rear mech - XT Shadow ('09)
Cassette - SRAM PG990 ('14)
Chain - SRAM PC991 ('14)

Thanks.

cooldad

Could be mud.
Could be worn chainrings.
Could be set up.
Mechs don't slip though.

The Rookie

A favourite is mud between the cassette sprockets lifting the chain off the teeth.....that would fit your description perfectly.

iwilldoit

Give it a good clean and take it for a ride if nothing else it will show you if it's the mud or not.

AlShack

Mine did exactly the same after I'd fitted a new cassette/chain/cables etc. Had all worked perfectly for the first ride, then the second ride it was jumping all over the shop. However, I was axle-deep in mud on that ride. Once cleaned off, it was back to slick-shifting and staying in gear.

Mud is evil, although quite good fun as well

cooldad

The cable outers settle and compress a fraction, so after riding for a while you need to tweak the indexing.

steelo

Cool thanks guys, I've cleaned it up so hopefully when I take it for a spin tomorrow it'll only need a slight tweak if anything. I think I may replace the middle chain-ring as well as it's had plenty of use and a new one will hopefully match up better with the new chain and cassette.