The axle walks in and out. This motion is perpendicular to the driveshaft(not trying to dumb it down, I just wanted to be clear to all) This motion pushes the pistons into their bores(a little) When you press your brake pedal it takes a little fluid to take up the slack. Calipers have large bores, so it takes more fluid to move the piston a given distance but at a greater mechanical advantage. This isn't a problem on the front because the front wheel bearings keep the discs at pretty much a static distance from the caliper. It doesn't matter too much that the chev calipers float. A full floater kit uses the same type of hub locating wheel bearings that the front does. Residual valves keep fluid in the calipers after you press the brakes. They can be bought with different holding pressures and yes the do cause a little drag. If anyone has a comment about my post feel free. <img src="/forums/images/graemlins/smile.gif" alt="" />