Originally Posted by seville
1. How often do you have to replace your brake pad? (how many miles?)
2. How much is it to replace?
3. What signs show that brake pads need to be replaced?
1) When they are close to the wear indicators; this differs in mileage based on how often you brake. A person who drives lots of highway miles will get longer brake pad service verses a person who drives lots of "stop and go". If you rotate your tires (and you should), you can inspect the thickness of the pads when the wheel is removed easily.
2) Depends on the quality of the pad you use. There are grade "silver", grade "gold", there are "yellow", there are "red", the list goes on.
3) One way to see how the pads are wearing is to observe the brake fluid level in the master cylinder. If the fluid drops below the "normal" line, the pads are wearing, and more fluid is ocupying the caliper pistons to keep the pads against the rotor. This method however will not work if you have your car serviced (i.e. oil changed by a dealer/service center), as they usually "top off' the fluids as a favor to you.
Best way is to either remove the wheels and inspect, or take it to a shop; most offer free brake inspections.
Couple of last points: front brakes account for 60% or more of your braking, so they may show more wear then the rears.
Changing the rear pads on our newe Mustangs requires a special tool to rotate the pistons into the calipers in oder to allow the new pads to be inserted. This is because the rear pads are also used as the emergency brakes, so they self adjust, and the pistons have a "ratchet type" method to compensate for wear.