Spongy Front Brake After Three Weeks Parked
Your 150 cc commuter has been parked under a porch for three weeks while you were away. On Monday morning you have 25 minutes to reach work, a 12 km ride. Quick checks: the rear tyre reads 18 psi (the manual says 29 psi solo, 33 psi with a pillion); the drive chain deflects about 45 mm at mid-span against a spec of 20–25 mm; the front brake lever comes back almost to the grip before it feels firm, and the reservoir window shows dark, cloudy fluid last replaced three years ago. Both tyres still show 2 mm of tread above the wear bar. The engine starts easily, the headlamp and horn work, and the helmet's strap and SIRIM label are intact. You decide to ride anyway because the workshop is shut and you cannot be late.
1. Sort your findings into 'do not ride' and 'monitor'. Justify each with the failure it could cause at speed.
Read the worked answer
The front brake is a stop-ride fault. A lever that comes back near the grip means the hydraulic system is not building pressure: air in the line, fluid that has absorbed water over three years, or a failing seal. Braking will be weak, inconsistent, and can disappear completely once the fluid heats on a long descent, so no amount of careful riding makes it safe. The chain at 45 mm is also a stop-ride item, but it is fixable in minutes: at roughly double the specified slack it can jump the sprocket under acceleration, lock the rear wheel, or crack the engine casing. The 18 psi rear tyre must be corrected before leaving - under-inflation makes the tyre flex and overheat, slows steering, lengthens stopping distance, and risks a pinch flat. The 2 mm tread, lights, horn and helmet are serviceable; monitor the tread and replace it before the 1.6 mm legal minimum.
2. You have only a petrol-station air pump, a pressure gauge and the bike's own tool kit. What is the correct order of work, and what would make you abandon the ride?
Read the worked answer
Do the cheap, reversible jobs first and leave the decision about the brake until last, because that is the item that decides whether the ride happens at all. Inflate both tyres to the manual figures while they are cold, using your own gauge rather than the station's, since those are often inaccurate. Then loosen the rear axle nut, adjust the chain at its tightest point, keep the wheel aligned on the swingarm marks, retorque the axle, and recheck the deflection at 20–25 mm before lubricating. Then test the brake: squeeze the lever several times. If it firms up and stays firm, the fault may be air that pumping has partly displaced - but if it fades again after ten seconds of holding pressure, or the lever slowly sinks, the master cylinder or a seal is failing. Abandon the ride. Also abandon it if the chain has kinked or tight links, or hooked sprocket teeth - adjustment will not fix worn parts.
3. The rider argues: 'I will just go slowly and use the rear brake only.' Explain why this reasoning fails.
Read the worked answer
It fails on physics and on risk. Under braking, weight transfers forward, so the front tyre carries most of the grip available; rear-only braking can use perhaps a third of the machine's stopping potential, which means a car pulling out 15 m ahead cannot be stopped for. A motorcycle that cannot brake hard is not a slow motorcycle, it is a motorcycle with no emergency reserve. The fault is also unpredictable rather than merely weak: a spongy lever can suddenly go to the bar when the fluid heats, or grab when a sticking caliper releases, and neither is controllable. On a wet road, rear-only braking locks the rear easily, and a locked rear wheel on a commuter ends in a low-side fall. Finally, riding a machine with defective brakes is an offence under the Road Transport Act, and if you crash you carry the fault for having chosen to ride it.