ABS light on, a spongy rear brake and a pillion on a bike that stood in the rain
Your 125 cm³ A1 motorcycle has stood outside in the rain for two weeks. Ten minutes before a 30 km ride to a friend's cottage you check it over. When you switch on the ignition, the ABS warning light comes on and stays on after you pull away; normally it goes out once the wheels have turned. The rear brake pedal has about 2 cm of free travel before it bites, compared with about 1 cm last month, and feels spongy. The chain has 40 mm of slack measured mid-run; the manual gives 25–35 mm. You have bolted on a 40-litre top box and plan to take your friend as a pillion; rider plus passenger is 150 kg against a manual maximum load of 180 kg. Tyres are at the solo pressures from the manual. The bike is not subject to periodic inspection in Finland, so no sticker tells you anything.
1. The ABS warning light stays on after you pull away. What does that mean, and does it stop the ride?
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On most bikes the ABS lamp lights with the ignition and goes out once the self-test passes and the wheels have turned. Staying on means the self-test has failed - a wheel-speed sensor, its connector, or the pump supply - so anti-lock is not available. The brakes will still brake conventionally, but on a wet, gravelly or leaf-strewn surface the main reason a rider stays upright under hard braking is gone, and a locked front wheel on a 125 puts the bike down almost instantly. It is not in itself a legal prohibition, but it is a defect in safety equipment, and the right call before a 30 km ride with a passenger is not to ride until it is diagnosed - especially as two weeks of rain point to a sensor or connector rather than anything exotic. Check the sensor gap and connector first, then a dealer.
2. The rear brake pedal is spongy with growing free travel. What are the likely causes, and how does that change your decision?
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A spongy pedal with growing free travel points to the hydraulic circuit rather than the pads alone: air has entered through a leaking banjo, a perished seal or a low reservoir; or the fluid is old and has absorbed water; or the rear pads are worn so the piston must travel further. Air compresses, so the pedal feels soft and the brake can fade or fail when hot. A partly lost rear brake costs stability in slow turns and on gravel, and a passenger adds mass that both brakes have to manage. This is a defect to fix, not to monitor: check the reservoir level, look for wetness around the caliper and line, check pad thickness, then bleed the system. Setting off on a 30 km two-up ride with a brake I already know is soft is the kind of decision that gets judged as negligence after a crash.
3. The chain is at 40 mm and you are adding a top box and a pillion. What do you do about the bike's setup, and what changes in how it rides?
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40 mm against a 25–35 mm range means the chain is loose: it can whip, slap the swingarm, skip a tooth under acceleration and in the worst case derail and lock the rear wheel. Overtightening destroys bearings, so I set it to the manual figure at the tightest point, following the manual's instruction on whether to measure loaded or unloaded. The top box and pillion change the geometry: weight behind and above the rear axle lightens the front, so I move to the manual's two-up/loaded tyre pressures and increase rear preload. 150 kg is within the 180 kg limit, but the box has its own load limit and must not be packed heavy. Handling will be slower to steer and slower to stop, so I ride accordingly - after the ABS and the rear brake are sorted, not before.