Here is something clever about your brakes: even as the pads and shoes wear down over tens of thousands of miles, the brake pedal stays at roughly the same height and feel. That is because brakes self-adjust for wear automatically. Disc and drum brakes do it differently.
How disc brakes self-adjust
Disc brakes self-adjust naturally through the caliper piston seal. When you brake, the piston pushes out to press the pad against the rotor. The square-cut seal around the piston flexes and, when you release, pulls the piston back just a tiny amount - only enough to release the pad. As the pad wears thinner, the piston simply rests a little farther out each time, automatically taking up the wear. No mechanism needed - the seal does it. See the caliper piston guide.
How drum brakes self-adjust
Drum brakes use an actual adjuster mechanism - a star wheel and lever. As the shoes wear and the gap to the drum grows, the adjuster advances a notch to take up the slack. On many vehicles this happens when you apply the parking brake or brake in reverse, which is one reason using the parking brake regularly keeps rear drums adjusted. See how the parking brake works.
What it means for you
- A pedal that gradually gets lower is usually NOT normal wear - self-adjustment should keep it consistent. It more likely points to air, a leak, or a fluid issue. See spongy pedal causes.
- Drum adjusters can seize from rust, leaving the pedal low or the shoes dragging - a reason to service rear drums periodically.
- Self-adjustment is why the fluid level drops slowly as pads wear - the pistons sit farther out, holding more fluid. A dropping reservoir can simply mean the pads are getting low.
The takeaway
Healthy brakes take up their own wear automatically, keeping the pedal consistent. If the pedal changes noticeably, that is a signal worth investigating - see brake pedal feel. Keep the wear items fresh with quality pads and hardware.