Most stuck rotors require just a couple wacks with a rubber mallet, but if you live in the rust belt, or if its been a while since your rotors have been changed; we’re working with seized rotors.
The problem with removing seized rotors are:
1. When you start working with small sledge hammers, you’re going to damage the rotor, and that means you’ll need new ones; even though they may be perfectly reusable.
2. The probability for collateral damage when swinging a small sledge at a rotor is pretty high. Likely the only open area you can hit is the gap where the brake caliper sits; the rest is covered by a dust shield.
The answer here is an air hammer, and soft tip bits.
The VIM AH100 set comes with a brass, plastic and an aluminum tipped bits.
The ability of one material to damage another is generally dictated by its MOHS hardness:
A soft material like Brass with a 3-4 MOHS will always damage before a material like hardened steel (rotor) which has a MOHS hardness of 7-8.
An air hammer, especially a reasonably powered one (like a Chicago Pneumatic CP7150), will be able to hit the back of the rotor exponentially more powerfully then anything you can do by hand.
The speed and vibration of the hits will aid greatly in loosening up the rust bond; and isn’t something you can mimic by hand.
Aim the tip of the bit against the backside of the rotor, right where the brake caliper would sit. The end result should be removed damage free rotor.