A brake drags / the wheel locks or overheats

On a disc brake, the caliper piston pushes the pad against the disc and then must retract slightly at rest (thanks to the seal's elasticity) to free the wheel. When it seizes — from oxidation (moisture, road salt), accumulated pad dust, aged brake fluid, or deteriorated seals — it no longer retracts: the pad stays pressed against the disc. Consequences: the wheel brakes constantly (hard to turn, slows quickly when spun), the disc gets very hot and can turn bluish, the pads wear quickly and unevenly, and the fluid can get hot enough to cause loss of braking. This is the most common cause of a dragging disc brake. Confirming signs: with the wheel lifted, it brakes on its own; and the disc in question is abnormally hot after a short ride. Since the caliper is part of the hydraulic braking circuit, restoring it (removal, freeing and cleaning the pistons, replacing the seals, greasing the slide pins, and above all bleeding the circuit) is classified expert-only: a mistake on this vital circuit can cause loss of braking. Leave it to a professional. As long as the wheel brakes on its own and the disc gets very hot, don't ride: risk of locking up when hot and destroying the disc and pads.

The master cylinder pressurizes the fluid when you brake, and must let that pressure drop when you release, thanks to a small compensating port linking the bore to the reservoir. If this port gets blocked (deposits from contaminated fluid, a swollen seal), or if the piston doesn't fully return (seizing, poor adjustment of the lever/pedal free play), the pressure doesn't drop: the brake stays applied constantly. The wheel then brakes on its own and the disc heats up, exactly like with a seized caliper — but here the problem originates upstream, at the master cylinder, and the fault can affect both calipers on the same circuit at once. This is a rarer but serious cause. To tell it apart from a seized caliper: if slightly loosening the master cylinder (or its mount/free play) releases the brake, it's the master cylinder; if the fault is limited to a single caliper, it's more likely the caliper. The repair (rebuild with a kit or replacement of the master cylinder, then bleeding) touches the heart of the hydraulic circuit: it's classified expert-only, left to a professional, since a mistake can lock the brake or cause loss of braking. Urgency: a brake that stays applied overheats and can lock the wheel — don't ride, get it towed or repaired on the spot.

Repair to be left to a professional.

On a drum brake (mechanically operated by cable or rod), the lever/pedal rotates a cam that spreads two lined shoes against the inside of the drum; a return spring brings the shoes back to rest when released. If the cable seizes in its housing (corrosion, lack of lubrication), if the cam pivots oxidize, or if the return spring weakens, the return no longer happens: the shoes stay partly extended, the brake drags, the drum heats up, and the wheel turns stiffly. This is the mechanical equivalent of a seized caliper piston, but on a drum brake (common on the rear of small bikes, cruisers, older models, and scooters). Diagnosis: with the wheel lifted, it brakes on its own and the control doesn't return cleanly. The fix (lubricating or replacing the cable, cleaning and lightly greasing the cam pivots — never the linings — checking the return spring, adjusting the free play) is an intermediate, mechanical job (no hydraulics), so more approachable than a caliper. On a vital component, rigor still applies, and you check that the shoes retract cleanly and the wheel spins freely afterward. Never put lubricant on the linings or the drum's braking surface.

Free play is the small amount of slack in the front brake control before it starts to engage; it guarantees that, with the control released, the brake fully returns to rest without dragging. If free play is insufficient or absent (poor adjustment, for example a rear brake pedal set too high or a drum cable too taut), slight pressure stays applied constantly: the brake drags, heats up, and wears, without any actual seizing. This is the simplest and most benign cause of a dragging brake, and the first to check since adjusting it is a free, easy DIY job. It mainly affects mechanical controls (cable/rod drum brakes, adjustable rear brake pedals). The principle: restore the recommended free play to eliminate any residual pressure, while keeping a clear bite point. Important: if, after restoring correct free play, the brake still drags, the problem lies elsewhere (seized cable, caliper or master cylinder not releasing) and you need to continue diagnosing. On a vital component, always check, wheel lifted, that it spins freely with the brake released after adjusting. This is often the good news of the diagnosis: a simple adjustment that fixes the dragging.