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Rear Mech / Cassette issue

jimsam33jimsam33 Posts: 59
edited May 2010 in Workshop

I have a new rear mech and cassette on my bike.

All went on well without any issues. Changes gear lovely, both on the stand and out on the road. I have done approximately 200 miles with them. The Hi, Low setup is great and the indexing is great with no chain rub/noise.

My issue is:

When I'm on the big chainring at the front and the bottom 4 gears (easiest ones)of the rear cassette you can't pedal backwards or the chain changes down one or to gears.

Not a problem on the road as you don't pedal backwards.

It is a problem when your doing some servicing, like putting some oil on the chain.
Trying to put your feet to the pedals to set off, You can't move the pedals round into the right position.

Could anybody tell me what the possible problem is:

Dodgy rear mech?
Dodgy cassette?
Something else.

Any help / advice greatfully received.


  • John.TJohn.T Posts: 3,698
    Many chain/cassette combinations will do this. Have you fitted the same make/model/size as before. If not this may be the cause of it happening now. It is due to the teeth cutaways that help with changing and the extreme chain line in those gears.
  • jimsam33jimsam33 Posts: 59
    Thanks for the info John.

    It is a different Mech and cassette size than originally. Same make though, Shimano mech and SRAM cassette.

    Good to know that it's common, and therefore not a problem that needs looking into further. That was the main thing. I can relax now and just get used to it happening on occasions.
  • John.TJohn.T Posts: 3,698
    It may well stop when they get bedded in. I had a similar problem with chainrings that went away after about 100 miles.
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