Maybe this will help
The brake pads appear to be resting on the rotor of the back wheel, even with the emergency and foot brake off. I've done a couple of test runs up and down the street to see if putting on the brakes quickly releases them, but it doesn't seem to. The brakes squeal loudly when I back up. Not so much when I go
disk brakes use disk pads to create the necessary friction to bring our Spyders to a halt. The brake pedal generates the forces to slam the pistons out of the calipers generating the friction to decelerate the rotors which in turn stops the Spyder.
First thing to discuss is construction of the caliper and what it does for us... The caliper is made of heavy cast metal to hold in place to anchor it place. It would not work well if it were flimsy made. The calipers hold what are called pistons, shaped like cups. These cups push out wards when we mash on the brake pedal.
What the piston cups do is press against the brake pads. The biggest difference between disk brakes and drum brakes is in the construction an activation and release actions. Drum brakes have brake shoes in lieu of brake pads. Brake shoes are returned to their neutral position by brake shoe return springs. Disk brakes don't have anything to return the pistons to neutral again. So when you release the brake pedal the pressure releases the pistons. So what you are seeing when you look at the brake disk and caliper is normal. Not being a brake engineer I am not up to speed on the clearance between a released brake pad and the disk rotor. But you can see it is not much probably in tens of one thousand of a inch.
Disc brakes make strange noises when lightly applied regardless of direction of rotation. Go look at the wheel that you can see the best. If you have a mirror on a rod or even a dental mirror will work, look at both sides of the caliper assembly and observe the mounting bolts. When you go forward the caliper resets itself to the front side. When you back up the caliper repositions it self to the rear of the mounting bolt holes. Both actions give you a slight clunk when the brakes are applied.
Disk brake squeals are the results of metal to metal vibrations caused by light applications of hydraulic pressure to the brake system. Irregular metal surfaces like between the pad and disk, metal pad backing plate and piston cup edges where try meet up cause squeals and chattering vibrations.
Disk brakes were designed to reduce heat and weight of the brake assembly sitting on he end of the axle shaft. Also to improve all around braking in hot, cold, wet and dry conditions and self clean and adjust themselves. Drum brakes need to be adjusted, cleaned at regular intervals.
disk rotor heating can be the result of several different things. One or both pistons not being released by the piston o-ring seal(s). Age, rust or debris build up on the smooth outer wall of the piston. One time I decided to change brake fluids on a dirt bike so I flushed the system really good and changed the fluid. Bled the air out. Tested the brakes. It stopped on a dime and gave me change so I went for a long ride. The o-ring seals swelled up reacting to the non-standard brake fluid and put the brakes on automatically on the first pull of the brake lever. But I could force the pistons back to a neutral position with a very big lever in the caliper. Needless to say I never did that again!
Hope this helps some or some one out
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