Problems after changing rear wheel
akilpatrick Posts: 3
edited May 2012 in Workshop
Hi - first post! I recently purchased a new pair of wheels. Took cassette off old wheel and put on new wheel. All went fine until out on the road. Now when I'm on the 50 ring I can't get into the biggest gear on the cassette ie the 25 on my 25-12. Just refuses to move across. Tried fiddling with barrel adjuster but just different amounts of clicking but no 25 gear. Grateful for any inspiration to fix..
Not all hubs are the same so even if the cassette fits on it might be 1-2mm or more off of its position on the old wheel.
Trek Madone 5.5c (2010) - For pleasure http://i1151.photobucket.com/albums/o62 ... G_0413.jpg
Can you get on the 25 when on the small chainring at the front?
The barrel adjuster will not fix this as that simply alters the cable tension to ensure smooth transition between cogs. It does not change how far the mech moves overall.
You may need a spacer on the new hub (as suggetsed) but if the cassette fits snug with no movement it is likely that it is already correctly fitted.
If the spacer is not the issue adusting the low screw so the mech aligns with the 25 cog (but does not go past it) should be the right fix.
It might be that your hub spacing is slightly different and the mech can't move sideways far enough, so you will need to adjust the limit screw a little to let it
The concern is that if it won't move far enough to get onto the 25, will it move too much at the 12 end ? You don't want the chain moving too far over as it'll get jammed between the cassette and the frame and that's dangerous, so you'll need to adjust the other limit screw a little to prevent it.
See http://www.parktool.com/blog/repair-hel ... derailleur
If you struggle and everything goes south you simply need to start over. (so note how many turns you do)
A good tip is to set up the screws without any cable in the mech. You can then re-connect the cable and test the shifting.
If the shifting is not crisp or does not move 1 cog for 1 click this can be tuned with the barrell adjuster (the H/L screws do not affect this).
Have a look at this YouTube video.
Explains initial set up for H and L screws and indexing clearly.
Should help you sort out the best set up for your new cassette