I looked at my old bicycle repair manual and went through the notes I had on shifters and found a bunch of things to measure and/or check. Most were hand written notes from some sessions we had with the old (I mean OLD) 7/11 cycling team back in the day.
- Make sure both derailleur pulleys are parallel with the front chain ring. I remember a tool that fit in the holes for both upper and then lower pulleys in place of the axle bolt and had a rod that would rest against the chain ring and the derailleur could be twisted to line things up. Some of the sprinters such as Davis Phinney were so strong they could twist things up pretty good.
- Make sure both pulleys are exactly over each other.
- Make sure the rear axle and cassette is 90 degrees to the line of the chain when the chain is in the mid gear and on which ever front chain ring you use most.
- Make sure the chain ring is completely flat. That was a problem with early Japanese rings as they were so soft.
- Make sure the length of the chain is correct for the gears. Just because it came on the bike does not make it correct. I had the steps to do it but now there is a website that calculates for you.
Bicycle Chain Length Calculator
Good luck