Originally Posted by
elcruxio
I've seen more than one official maintenance manual outline that exact procedure for lining up the calipers. SRAM was one of the offenders. Lining up manually by eye is something I haven't seen in a maintenance manual ever. Then again it's been a few years since I read about lining up calipers. But it could be that some mechanics go with the bad info they get in tech docs because it's convenient and they can claim it's official.
But another trick on the same vein is adjusting pistons manually. Sometimes one of the pistons is a bit dominant or more protruded, which can cause the pads to twist the rotor slightly when braking. That can cause noise or be felt as vague bite point. The way to correct that is to put s small screwdriver behind the non dominant pad (not between the piston and the pad!), and push the pad towards the center whilst simultaneously slightly pulling the brake lever. This should push the dominant piston back a bit and allow a more even contact.
You're bringing up another problem that is common on used caliper - asymmetrical piston drag. I will generally pull the pads and wheel and hold the more mobile piston fully compressed and pump the other in and out a few times. Also a good time to clean and lube the pistons.
But that's different than having the caliper twisted because the rotor is too flimsy to overcome the drag of semi-tight bolts, and won't center the caliper if there is a gap under it from loose bolts.
Manuals suggest techniques that a consumer is expected to be able do with only moderate mechanical skill. But current hydraulic brakes benefit from a wide range of techniques that no manufacturer publishes. Bikes are becoming non-serviceable by amateurs.