Hi 83,

I'm not convinced that either of these AZ calipers are actually stuck.

I haven't bought calipers in a long time, but I've rebuilt well over a dozen, and all are performing satisfactorily. I dry fit the pistons, but they all require clamping pressure to retract after assembling with a new sealing ring. I think it unreasonable to expect a new caliper to behave the same as one with a worn seal.

You don't mention any observations at the offending wheel with it jacked up and
applying the brakes. Have you done that ?

It's also curious that you had no indication of the original stuck caliper until it began grinding your rotor, but now 2 new ones are causing a shudder.

The other variable in the equation is that you've changed rotors, so I would double check the run out, but that would usually reveal itself while braking and not as you describe.

A rear end shudder on deceleration could possibly be a u-joint. It's a long shot, but it's coincidence with your brake work might be explained by your original sticking caliper having a dampening effect, and now with free brakes it's more pronounced. Might be worth a look.

This is assuming that you're not using deceleration as a synonym for braking.

regards, Peter