Problems after changing rear wheel

akilpatrick

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..

JamesB

try adjusting stop screws on mech; if hub spacing / freehub slightly different then will need to adjust derailleur `throw`

nickellis

I'm a bit a of a novice when it comes to cassette changing too. But think that possibly you might need a spacer on the hub between the cassette and the centre of the hub.

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.

smidsy

It would seem your new wheels have a built in 'anti crossing' device fitted :-)

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.

andy_wrx

As above, if the cassette fits snugly - you can't waggle or rattle it about by hand with the wheel off the bike - then you don't need to fit a spacer.

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

akilpatrick

Thanks all - cassette "seems" not to wiggle about and can't get 25 cog on either 50 or 34 rings. I tried to change up past the 12 ring whilst riding last week and think chain came off temporarily so looks like need to adjust the H/L screws on rear derailleur to get them back in sync. I've already been warned of the dangers of adjusting too much allowing chain to shift onto spokes!

smidsy

Just adjust the screw slowly until visually the jockey wheel lines up with the 25. Then gently push on the mech to check it does not move. If it is adjusted correctly you will not be able to push the mech so your spokes will be safe.

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).

arlowood

Hi there

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

http://www.youtube.com/watch?v=SkzvfCaIbyQ

andyrr

You shouldn't really be using the big/big or small/small combinations front/rear : you are asking your chain to run at a more acute angle than is ideal, better, once you are approaching these extremes, eg big front and 2nd biggest rear, you then shift to using small front and then you'll need to knock the chain down a couple ofprockets on the rear (to smaller ones). I think it ok to run the extremes for short periods but I try and avoid it in general.