Gear / chain clunk issue...

Check the bushings AND/OR connections for your swing arm and/or suspension linkage ...

Your chain and sprockets may be worn out.

thanks for your replies, i've had a look at the bottom bracket which seems pretty solid. I then realised that the chain only jumps under pressure on the bottom two sprockets of the rear cassette. I've not taken it apart to have a look yet as i dont have the tool but can these slip? i was under the impression they were sepearate from the main block?

stinet said:

thanks for your replies, i've had a look at the bottom bracket which seems pretty solid. I then realised that the chain only jumps under pressure on the bottom two sprockets of the rear cassette. I've not taken it apart to have a look yet as i dont have the tool but can these slip? i was under the impression they were sepearate from the main block?

Presuming you have a Shimano rear derailleur, you can vary the chainwrap by adjusting the 'B' screw that is located near the rear derailleur hanger bolt -- having the chain in contact with one-more tooth on a given cog may be sufficient to resolve your problem ...

The adjustment to the 'B' screw is most easily done when the derailleur is NOT attached to the frame otherwise you are (essentially) grinding the tip of the screw into the derailleur hanger as you attempt to make the adjustment ... you do NOT need to detach the cable.

... but, you probably should NOT be starting from a dead stop with the chain on the smaller cogs ... it's just not as efficient as being on an intermediate cog, accelerating, and then upshifting to the smaller cogs.

BTW. The smaller cogs can "slip" if the lockring is loose ... but, then you would have found yourself on the ground.

How old is your chain? Have you measured it for wear?

thanks for the replies guys. My bike got stolen the other day so this is no longer my issue! on the bright side i picked up a new (used 3 times) saracen zen (rrp £500) off ebay for £101.01, And theres no problems with that! 🙂