indexing out, or mech need adjusting?

[alecstilleyedye]

i put a new wheelset on one of my bikes last week, and the rear gears seem to auto-shift down the cassette between the 3rd and 4th largest sprockets (out of 8).

you get the noise that indicates that the indexing is out just before, at which point you can prevent it happening by trimming the right shifter (shimano sora).

i don't want to start fettling one thing if i'm not sure it's what i should be fettling.

ta in advance

 

[Chris James]

If it sounds like you are running noisily then the indexing is probably out.

You say it is a new wheelset? Perhaps it is spaced slightly differently than the original one? If the stops are okay and you can still get into top and bottom gears then you just need to play with the barrel adjuster after working out if it is running high or low.

 

[alecstilleyedye]

i should have pointed out that it is a preexisting cassette, not a new one. it does shift into all sprockets so it does sound like the indexing.

how do i know if it's running high or low? and which way do i turn the barrel?

 

[Landslide]

My guess'd be the cassette is sitting in a different position on the freehub relative to the mech hanger.
I'd re-set the stops, then get the indexing set so it's happy shifting from the smallest sprocket to the next-to-smallset.

 

[Chris James]

If you know the bottom stop is okay then put it into bottom gear.

Then change up one gear using the shifters. Does it shift into second at the back? Also get low and see if the chain looks like it is lined up correctly on the sprocket.

For the rear you change up (harder to pedal) by releasing cable tension. So if the mech is not getting into second or is barely there then you have too much tension and you need to screw the barrel adjuster into the mech to reduce the cable tension.

On the other hand if the chain looks like it is going too far then you need to take up tension by screwing the barrel adjuster out. The adjusters have a standard right hand thread so you screw in clockwise and out anticlockwise.

You can see the derailleur shift when you adjust the barrel adjuster (as long as you are not at one of the stops!) so this will confirm to you that you are adjusting correctly.

Just do a little at a time! Ideally you want to ere on the side of having the cable tension as high as possible while still indexing fine to allow for any future cabel stretch.

Check you can index okay right across the cassette. Then go for a slow ride and check you can still index okay!

Setting up indexing is pretty easy but I find it is best to only make small adjustments and check.

 

[stephec]

Take a look at this -

http://www.parktool.com/repair/readhowto.asp?id=64

you should find the answer in there.

 

[fossyant]

Get on your knees and check if the top jockey is in line with the sprocket you've selected. Different makes of freehub will be a mm out from each other, even if you use the same cassette. Quarter turns until it's smooth again - use the barrel adjuster on the mech !

 

[mickle]

My guess'd be the cassette is sitting in a different position on the freehub relative to the mech hanger.
I'd re-set the stops, then get the indexing set so it's happy shifting from the smallest sprocket to the next-to-smallset.

Landslide is right.