I just dissected a thread from 2005 about rear brake pads being too tight, rotor overheating, etc. I put new (HD) pads, rotor, wheel bearings, tire & caliper seals, pins & pistons on my '00 Road King. Afterward it was a little snug turning the R wheel while on the jack & backing up in "N". New pads & rotor??? I went on a 2.5 mile ride (city). I lost the rears about half way. Upon return the rotor had blued where the pads ride. I don't recall if I had pressure build-up in the caliper afterwards, but I did in the master (I'm sure the fluid had boiled, due to complete lack of pedal pressure). I re-bled the system & drove it a mile using the rears (& fronts) about 4 or 5 times. I didn't lose the pedal but the R rotor was HOT, the fronts were still cold. Another mile would've easily been enough to transfer enough heat to boil the fluid again.
Somewhere along the line I ended up with @ 1/16" freeplay in the outer pad. :<) Inner pad was still tight :<(. I have that PITA caliper that requires axle removal (4 piston caliper). If I pry inward on the caliper from the swing arm, the tire/wheel spins freely. I miced (sp) a new piston from a spare kit & compared it to one of the old pistons. Battery's dead in my micrometer but I would guess the new pistons are @ .004" taller. Which would probably be enough to gain enough clearance to make everybody happy & spinning freely. I'm not sure how I'm gonna fix this w/o taking everything back apart, but.......any suggestions other than pounding the crap outta the caliper assembly with a HEAVY mallet bending it slightly inward? I actually did that & it's actually....better, but not perfect. I guess I could try flat sanding the inner pad. Food for thought....or not.
And, HEY all you genius engineers: How about looser & self adjusting clearances along with some kind of piston/pad return mechanism?