Brake, Suspension and Steering Systems
Brakes
Hydraulic disc brakes: lever/pedal, master cylinder, hose, caliper with pistons and seals, pads, disc. Hydraulic principle: pressure is equal throughout a closed system, so a larger caliper piston area multiplies force. Know the difference between fade (heat reduces friction), spongy lever (air or moisture in fluid, or a soft hose) and dragging brake (seized piston, blocked return port, misadjusted pedal). Brake fluid is hygroscopic - it absorbs water, lowering boiling point - so change it on schedule. Never top up with the wrong DOT grade or mix mineral and glycol fluids. Bleed from the furthest point, keeping the reservoir from running dry.
Drum brakes: leading/trailing shoes, self-servo effect, adjustment and contamination by grease.
ABS: wheel-speed sensors, hydraulic modulator, and the rule that ABS does not shorten stopping distance on loose surfaces.
Suspension
Telescopic forks with springs, damping and oil; rear monoshock or twin shocks. Terms: sag (static and rider), preload, compression and rebound damping. Too little rebound damping gives a pogo effect; too much gives a harsh, packing-down ride. Fork oil level and viscosity change damping. Worn seals show as oil on the stanchion.
Steering
Head bearings (ball or tapered roller) need correct preload: too loose gives a knock and weave, too tight gives heavy, notchy steering. Check for a centre wear notch. Wheel alignment, tyre pressure and bearing play all affect stability.
Traps
Confusing fade with sponginess; adjusting preload to change ride height without understanding sag; over-tightening head bearings to cure a wobble.
Rule of thumb
Set sag first, then damping, then check steering bearings and tyre pressures - suspension complaints are often setup, not parts.