Rear mech - not moving all the way up cassette

[Paul_iow]

I have just fitted a new rear wheel with a different size cassette, still a 7 speed as was the original, with a new chain and now when I go to change gear I can only select half of my cassette. When I select the lowest gear with the shifter the chain moves half way up the cassette but not to the bottom gear. When I manually put the chain on the lowest gear with it also selected on the shifter the chain immediately jumps back up 3 gears. Please help!!!

 

[awfulquiet]

Sounds like you need to adjust the stopping points of your rear derailleur...

Or, if you jumped from a 12-25 to a 13-34, you may need a new derailleur if the arm isn't long enough...



This may help you... http://www.sheldonbrown.com/derailer-adjustment.html

 

[Paul_iow]

thats my 1st plan, just been watching videos as the written guides confuse me. Im not sure of the numbers, its raining at the moment so cant check, but ive gone for a smaller cassette, something like 27-12 to 24-12, might have the numbers wrong but the lowest gear certainly has less teeth than the old one. So the arm should be long enough?

 

[Paul_iow]

Its a shimano sora mech, ill have a look and find out what it can be used for. The old cassette definetly had more teeth though so heres hoping!

 

[HLaB]

If the H & L limit screws haven't been changed I don't think they'll need adjusting; it sounds more likely to the gear cable might of stretched. Alternatively I think if the new cassette is significantly smaller than the old a shorter chain will have been needed if not the deraileur would move to a more compact position than before introducing slack into the system that way. Somebody more adept with gears can probably explain better.

 

[PpPete]

New cassette on a new wheel ?
The H & L screws and the cable tension may have been (mis-)adjusted to fit something that wasnt quite right with the old wheel?.

 

[mzm70]

I'm with PP, I use a spare wheel for the turbo, when I swap between a Shimano WH-R600 and a Planet X Model B both on 10-speed cassettes, I have exactly the same problem, it's cable tension. Get a rag and pull the shifter cable tight and see if shifts to the inner most cog, for me it's a process of retensioning the cable.
HTH