Braking Systems, Adjustment and Roadworthiness
What the exam tests
Drum and disc brake construction, adjustment and hydraulic service, plus the checks a two-wheeler must pass to be declared roadworthy.
Drum brakes
The cam spreads leading and trailing shoes; the leading shoe self-energises and wears faster. Adjust the cable or rod so the wheel spins freely with slight drag, then check the brake arm and return spring. Replace shoes as a set and keep grease and oil off the linings.
Disc brakes
A master cylinder pushes DOT 3 or DOT 4 fluid to the caliper piston, and the square-cut seal retracts the piston. Check pad friction material against the limit, disc thickness with a micrometer, disc runout with a dial gauge, fluid weeping at banjo and piston seal, and the reservoir level.
Bleeding
Top up the reservoir, fit a bleed tube to the caliper nipple, pump and hold the lever, open the nipple to release air, and close it before releasing the lever. Repeat until no bubbles appear and the lever is firm. Never reuse old fluid, which absorbs moisture, lowers the boiling point and causes fade.
Roadworthiness
Checks include brake performance, tyre condition, steering play, lights, horn, mirrors, a valid PUC certificate and a rear-view mirror. A spongy lever, a pulling brake, a dragging wheel or a cracked tyre fails the vehicle. A road test confirms straight-line stopping without lock-up.
Worked example
A rider reports that the front lever comes back to the grip after the machine stood for a season. Reasoning: storage lets moisture enter and air collect, so the lever feels spongy and pumping restores it briefly. Flush and bleed with fresh DOT 4, check for leaks at the caliper and master cylinder, then re-test.
Traps
Mixing DOT 4 with mineral oil, contaminating pads with oil, overfilling the reservoir so the brake drags when hot, setting the rear brake so tight that the wheel cannot turn, and ignoring a scored disc.