In every single case, unless the derailleur is twisted and no longer stays parallel as it moves, if you cannot tune all gears in, your hanger is crooked.
It is that simple, yet people deny this over and over again.
Pretty much every bike that comes in for service, the hanger is bent to some degree.
No they are not aligned if you bolt on a new one.
It may not be aligned if you change wheelsets and there is significant dropout wear.
But if you can tune in part of the cassette and not the rest, it is bent.
Don't tell me it is not and it is some mystery thing that nobody else has had to deal with.
It's bent, get it aligned, ride the frucking bike.
You mad bro?
It possibly could be the hanger; yet, the issue is all the gears tune up fine except a middle gear that clicks slightly only under riding conditions and not on the stand. I did have the Park Tool for the hanger; yet, used it so seldom that I just have the LBS check it when I go in; and, like my annual checkup, it's fine.
I do swap cassettes and wheels though. I'm learning that a wheel swap can change the location of the derailleur in relationship to the cassette as some rear wheels are "dished" more than others. Likewise a cassette swap going from an 11-28 to 12-25 also changes the distance and angle of the gears to the rear pulley.
From Sheldon "Click" Brown
Angle adjustment ("B-tension") Modern derailers have two spring-loaded pivots. The lower pivot, sometimes called the "a pivot" winds the cage
up to take up slack as you go to smaller sprockets. The upper "b pivot" adds additional slack take-up ability by pushing the derailer's parallelogram backwards.
The tension of the two springs needs to be balanced for best shifting.
Most derailers have an angle adjustment screw (Shimano calls it "B-tension adjustment"). This adjusts the tension of the upper ("b") spring of the parallelogram, and thus the height of the jockey pulley
. The looser this screw is, the closer the jockey pulley will be to the cluster.
The angle adjustment will need to be set according to the size of the largest rear sprocket. If you change to a cluster with a larger or smaller low-gear sprocket, you will need to re-adjust this setting. You will also need to adjust this if you change the length of your chain.
If the angle adjuster is set too loose, the jockey pulley will bump into the largest sprocket when the bicycle is in the lowest gear (large rear, small front). This is the gear you should check the adjustment in. A larger low-gear sprocket may require a different rear derailer, for enough angle adjustment to clear the sprocket. In extreme cases, such as with a Shimano 36-tooth sprocket, a longer angle-adjustment screw may be needed -- some people even install the screw backwards.
Since a derailer shift is caused by forcing the chain to run at an angle, the greater the angle, the sooner it will shift. The closer the jockey pulley is to the cluster, the sharper the angle will be for a given amount of sideways motion of the derailer. Thus, the looser the angle adjuster screw is, the better the shifting will be.
Indoor Triathlete - I thought I was right, until I realized I was wrong.