Three symptoms before a 120 km trip
It is Saturday morning and you plan a 120 km round trip, half of it on motorway. The bike is a four-year-old 700 cc twin with 19,000 km on it. On a test ride around the block you notice three things. The front brake lever comes back noticeably closer to the grip than it did a month ago, and feels spongy when you hold pressure on it. The fluid in the reservoir window is dark amber rather than the pale straw colour you remember. Under a firm stop from 50 km/h there is a rapid judder through the bars, but no pulsing at walking pace. Back in the garage you measure the front tyre at 1.9 bar against a specification of 2.4 bar, and the chain has about 35 mm of slack with a noticeable tight spot when you turn the wheel by hand. The front pads still have 3 mm of friction material, and it has been raining hard for three days.
1. What explains the spongy lever and the dark fluid, and do you set off on the trip? Reason it through.
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The fluid. Brake fluid is hygroscopic: it absorbs water from the air over time. Four years is well past the usual two-year change interval, and dark amber is the visible sign. Water contamination lowers the boiling point dramatically; on a motorway with repeated hard braking the fluid can vaporise in the caliper, and vapour compresses. The lever then comes back to the bar and you have effectively no front brake.
The sponginess. Air or vapour in the hydraulic circuit, or a failing master-cylinder seal, or a hose bulging under pressure. Topping up the reservoir does not fix any of these - it hides the symptom.
Decision: no, you do not ride it. A front brake that changes feel is a safety-critical fault with no roadside workaround. Bleed and replace the fluid, check for leaks at the banjo bolts and caliper, inspect the hose, and if the lever is still spongy on fresh fluid, suspect the master cylinder. Rain and a 120 km trip are irrelevant next to this.
2. You also have a judder through the bars under firm braking and a front tyre at 1.9 bar instead of 2.4. How do you work out which is causing what?
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Start with the cheap, reversible variable: pressure. 1.9 against 2.4 bar is about 20 percent low. An underinflated front tyre flexes far more under braking, which can produce a shudder and also causes irregular wear (cupping) that feeds the judder back. Correct the pressure, then retest - some of the judder may simply disappear.
If it persists, look at the brake. A warped or unevenly worn disc gives a judder that scales with braking force and often pulses at low speed too. Uneven pad deposits from a few hard stops and then standing can do the same. Measure disc runout rather than guessing.
Check the front end. Loose or worn steering head bearings show up as a clunk or a shake under hard braking; test by holding the front brake and rocking the bike. Wheel bearings and a poorly seated tyre also qualify.
Order matters. Pressure first, then a re-test, then discs, then bearings - cheapest and most likely first, so you do not replace a disc that was only a soft tyre.
3. The chain shows 35 mm of slack with a tight spot. What is the risk and what do you do before the trip?
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Why 35 mm matters. Excessive slack lets the chain slap, whip and, in the worst case, ride off the sprocket or jam - a locked rear wheel at motorway speed. It also accelerates sprocket wear, and a loose chain on a wet, salty road after three days of rain is exactly where corrosion and stiff links appear.
The tight spot is the real finding. A chain that is tighter in one part of its run is either unevenly worn, has a partially seized link, or the rear sprocket is out of round. Set tension at the tightest point, not the loosest - if you adjust at the slack section, the tight spot will be over-tensioned and will destroy the gearbox output bearing.
Action before the trip. Clean and lubricate, rotate the wheel and inspect each link for stiffness, adjust at the tightest point to the manufacturer's figure, and check the sprocket teeth for hooks. If the tight spot cannot be worked out, or the chain has done high mileage, replace chain and sprockets together rather than riding 120 km on it.