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.
You need to turn the E break adjuster in to set the travel of the caliper. This has been explained many times. Look it up, it is dead simple to do and your problems will go away. Larry