Gear problem

[RufusChucklebutty]

Got a problem with my MTB gears, they shift OK and I can't see any stiff links or problems when its on a stand, I get big clunking and slipping chain on the middle sprockets 4,5,6, all the rest work fine.

I can't see the problem while riding, and it doesn't happen on a stand, cable tension on the rear deralier makes no difference.



Anyone got any ideas ?

 

[Threevok]

Sounds like a worn cassette.

Are those particular gears most used ? I use those quite a lot off road.

If it is the cassette change the chain at the same time

 

[Racing roadkill]

Wind the B screw on the rear mech all the way out, until the top jockey wheel is just shy of the biggest sprocket. Shift up and down the cassette a few times, then with the chain back on the largest sprocket, wind the B screw in, until the jockey wheel is clear of the sprocket, then re do the indexing.

 

[Brandane]

Possibly a bent rear derailleur (or hanger, more likely)? If that's out of line then you'll never get everything else working as it should. A good investment is a derailleur alignment tool.

Like this one.

 

[JuhaL]

I just bought Park Tools hanger alignment tool and it was worth for money. Even new bikes might have bent hanger, it's not unusual and doesn't need much force. But wind the b screw is good idea too.

 

[RufusChucklebutty]

Found the tool on special offer, I might get one.

http://www.chainreactioncycles.com/..._dt|pcrid|294922111655|pkw||pmt||prd|439096UK

 

[Threevok]

While a bent hanger can cause indexing problems and unintentional gear shifting, I doubt if it would cause the slippage under load you describe.

I would expect the b-screw issue to cause problems on most (if not all) gears, not just 4,5 and 6, so I don't think its that either

I suspect this is a drive chain wear problem - most likely the cassette. How old is it ?

 

[RufusChucklebutty]

I tried the B screw adjustment but it made no difference in any position.

I have made this bike out of a collection of spare bits, the sprockets look clean and not worn, but i will need to double check, and the chain is new, ive found a couple of youtube videos that say my symptoms are worn out sprockets, which is why the mid range ones have worn first, I will swop the cassette and see what happens.

 

[Ajax Bay]

You cannot tell by looking at a cassette whether it is is worn. I'm with @Threevok here. The symptoms described are of a new chain on worn sprockets (often the most used ones slip first). If the chain is still newish, the OP will probably get away with it provided the cassette is changed pronto (minimise use on those sprockets till then by greater use of other chainrings and the larger and smaller sprockets). I have managed (to carry on and complete) a long (100+km) ride (road with hills) with this issue: with a triple I just used 1 and 2 and 8 and 9 on the cassette with 52/42/30. Lots of double shifting.