Brake Inspection

Brakes are the single most critical safety system on any vehicle. They convert kinetic energy — the energy of a moving vehicle — into heat energy through friction. When the driver pushes the brake pedal, hydraulic pressure forces brake pads against spinning rotors. The friction slows the vehicle. Simple concept, absolutely critical execution. A brake inspection tells you whether this system is safe to operate or whether it needs service before someone gets hurt.

Brake pads are the wear item in the system. They are blocks of friction material bonded to a metal backing plate. New pads typically have 10 to 12 millimeters of friction material. The minimum safe thickness is generally 3 millimeters — below that, the pad needs to be replaced. Measure pad thickness with a caliper or a dedicated brake pad gauge. Measure at the thinnest point of the pad, not the thickest. Uneven pad wear — where one end of the pad is thinner than the other — indicates a caliper that is not sliding properly. Both inner and outer pads should wear at approximately the same rate. If the inner pad is significantly thinner than the outer, the caliper slide pins are probably seized.

Brake rotors are the metal discs that the pads clamp against. Rotors have a minimum thickness specification stamped or cast into the rotor — usually on the hat section or the edge. Measure rotor thickness with a micrometer at the thinnest point. If the rotor is at or below minimum thickness, it must be replaced. Do not machine a rotor below minimum thickness. A thin rotor cannot absorb and dissipate heat properly, which causes brake fade — the brakes get hot and stop working when you need them most. Rotor runout — the amount the rotor wobbles as it spins — is measured with a dial indicator mounted to a fixed point while you rotate the hub by hand. Maximum allowable runout is typically 0.002 to 0.003 inches. Excessive runout causes a pulsation felt through the brake pedal during braking.

Beyond measurements, visually inspect every component. Check brake lines and hoses for cracks, bulges, leaks, and chafing. A rubber brake hose that is cracked or swollen can fail under pressure, causing complete brake loss at that wheel. Check caliper dust boots for tears — a torn boot allows dirt and moisture into the caliper bore, which corrodes the piston and causes the caliper to seize. Check rotor surfaces for deep scoring, heat spots — blue or dark discoloration from extreme heat — and cracks. Check that caliper slide pins move freely. Check brake fluid level in the master cylinder reservoir. A low fluid level often means the pads are worn thin — as pads wear, the caliper pistons extend further, displacing more fluid from the reservoir. Or it means there is a leak somewhere in the system. Either way, it needs attention.