Brake rotors and pads

brakes

#1

I’m wondering if there should be a noticeable gap between the brake pads and rotor when the brakes are not applied. My front end pads are always touching on my 2004 chevy impala. I’m wondering if my calipers may be stuck.


#2

All disc brakes I’ve worked on have no gap, so it’s OK, as far as I know.


#3

System normal.Good indicator of stuck caliper is one pad showing a different amount of wear that the other(inner compared to outer)


#4

This is correct.


#5

There are two things that pull your pads away from your rotors: The square seal around the caliper piston pulls the piston back a few thousandths of an inch when you take your foot off the brake. This does not pull the piston free from the rotor on most cars. That is, the wheel will not spin freely when you jack up the car, it still rubs a little on most cars. The more important mechanism happens only after you get rolling. The pad ‘flys’ on the boundary layer of air that spins with the rotor. You can also think of it as the air acting as a lubricant. The pad does not touch the rotor once you get past about 30 mph.

As Oldschool correctly noted, a stuck caliper will manifest itself in one pad wearing more than the other, or in the case of a floating caliper, both pads on that wheel will wear faster than the pads on the other side of the car.

Actually there is one more mechanism that pushes the pads away from the rotor - flex in the hub on hard cornering or loose wheel bearings. People who weekend race street cars are very familiar with this one. After a set of tight ‘S’ turns, they have to push the pedal nearly to the floor the first time before the brakes hook up.