If you're worried about it (and for best performance) you want the rotor to run right down the middle of the calliper, and you want to pistons to all advance evenly. *You can push the pistons back into the calliper on one side, and you can advance the pistons on the other side by pumping the brake lever. Line the calliper up over the rotor and tighten the calliper bolts, then fiddle around getting the pads in the right position.
Or you could do what most people do and loosely mount the calliper, squeeze the lever so the pads are holding the rotor tight and then tighten down the calliper bolts.

I just went through a similar thing, I had sticky pistons that were advancing completely unevenly and causing a tonne of brake drag. So I cleaned the calliper and lubed the piston seals. Got the callipers and pads all lined up nice when reinstalled. Mine are the old tokico callipers with the 4 pads per side.

* Be aware that pushing 1 piston in will likely cause one or more of the other pistons to advance.

 

OP....

That is pretty typical, and not an issue.

The pistons of the caliper move towards the rotor as the pads wear, the caliper body itself is in a fixed position as is the rotor itself via being bolted to the wheel hub and the wheel spacers/axle/pinch bolts etc.......

But a good measure of cleaning of the calipers routinely and of the rotor buttons is always a good thing! along with flushing the braking system to all new fluid annually......it would only take about 8 ounces to flush completely both fronts and the rear.so it is a dirt cheap procedure- even when you use the best DOT 4 brake fluid out there, Motul RBF600, RBF660 or RBF700

You certainly can and should give the brake lever one single squeeze with one caliper removed and see how the pistons advance, and then clean all of the pistons and the spring steel guides the pads move on, then compress the pistons to open the gap for reinstallation.......

 

Riderseventy7 - thanks, sounds good. Don’t think I have quite the same issue but the alignment trick sounds like something I’ll do. last time I had the wheels off to replace tires I did the Dave moss method of caliper on, loosely bolted, spin the tire and apply the pads to make sure the pad and rotor surfaces are square. But that means the pistons would have met their previous position with NO further centering. I’ll manually fiddle with it.

riverszzr - thanks for the reassurance. By buttons, do you mean those rivets that hold the semi float rotors? (Black part to brake disk). A buddy and I had a debate if those should be able to rotate freely, never got a final answer - so… should they? Or just de-gunking is good enough?

I’ll give the lever a squeeze with the caliper off to test and clean the pistons before doing the centering procedure above. Just did fluid flush over the winter, and could probably stand to clean the caliper and pistons since it’s been about two years since the last deep cleaning. Probably get in there with a toothbrush and soapy water since I don’t want to use brakleen.

 

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riverszzr - thanks for the reassurance. By buttons, do you mean those rivets that hold the semi float rotors? (Black part to brake disk). A buddy and I had a debate if those should be able to rotate freely, never got a final answer - so… should they? Or just de-gunking is good enough?

I’ll give the lever a squeeze with the caliper off to test and clean the pistons before doing the centering procedure above. Just did fluid flush over the winter, and could probably stand to clean the caliper and pistons since it’s been about two years since the last deep cleaning. Probably get in there with a toothbrush and soapy water since I don’t want to use brakleen.

Not rotate freely with just your fingers, but they should rotate.

and yes a good cleaning while you rotate them

my method of rotating is simple........... bolt through the hole, double nutted inside, then simply use a wrench on the outside to spin them (one at a time of course)

 

Sounds like a plan. Thanks!

 

The Dave Moss method is def the correct way! And I def agree with what the other said!