Ok, so I'm having a running battle with my brakes. A little history: I have an 88 cradle with 88 vented on the rears, stock 86s on the front. I have no ebrake cables on the rears.
I have bled the crap out of them, but they are still spongy. If I pump them up the get hard in 2 pumps and hold firm. There are no leaks I can find front or rear.
I had the rear wheels off to bleed, so I had my son push the brakes. On the passenger side I noted that the pads were back from the rotor a bit, and had to move a fair bit before contacting the rotor. When he came off the pedal the piston receded again, leaving a visible gap to the rotor. The piston contacting the rotor co-incides with the pedal firming up. I've seen this before when the bearing is shot and the rotor wiggles the pads back, but never on a stationary assembly.
On the driver side this did not happen, the pads stayed close to the rotor and just clamped and released.