This is two bits not one, right?

[Darius_Jedburgh]

Put the bike in top gear - big front, small rear.
Disconnect the cable.
Check that rear mech and jockey wheels are perfectly in line with top gear. If not adjust stops.
Reconnect cable making sure you leave no slack.
That "should" give you perfect gear changes.
You may have to twiddle the above nut- once you have all three parts back in place - but you shouldn't need much adjustment.
If cable is new it will stretch in time when you can give a few more tweaks to your nut.

 

[swee'pea99]

Put the bike in top gear - big front, small rear.
Disconnect the cable.
Check that rear mech and jockey wheels are perfectly in line with top gear. If not adjust stops.
Reconnect cable making sure you leave no slack.
That "should" give you perfect gear changes.
You may have to twiddle the above nut- once you have all three parts back in place - but you shouldn't need much adjustment.
If cable is new it will stretch in time when you can give a few more tweaks to your nut.

Fantastic. Thanks. Having said which, I just got back & it's all running sweet as a nut & tickety-boo. Hooray!

Thanks again everyone

 

[raggydoll]

Well done for fixing it!

 

[mickle]

Woah there! That. Is not. A derailleur cable adjuster. It's a brake cable tension adjuster missing its little rubber ringed nut which screws up and down it. The flat in the side stops it from turning in the D shaped hole of the brake caliper when you turn the little rubber ringed nut.

 

[roadrash]

@swee'pea99 in my opinion , this is the best video with regards to indexing gears.

 

[raggydoll]

That is a really good video.
Nice and clear.

 

[swee'pea99]

@swee'pea99 in my opinion , this is the best video with regards to indexing gears.

Thank you. I shall watch and learn (and bookmark!).