Brake and drivetrain repair

Rim brakes press a pad against the side of the rim. They're simple, they're cheap to service, and their weakness is that they use your wheel as the braking surface — a rim that's out of true rubs, and a worn rim eventually has to be replaced. Adjustment is a cable-tension and pad-alignment job.

Mechanical disc brakes pull a caliper with a cable, squeezing pads against a rotor at the hub. All the same cable rules apply: they stretch, the housing gets contaminated, and they need periodic retensioning. The advantage is that the braking surface is a cheap steel disc instead of your rim, and a wobbly wheel doesn't affect braking.

Hydraulic disc brakes replace the cable with sealed fluid. Nothing stretches, so they hold their adjustment far longer, and they're much more powerful for the same hand effort. The trade is that when they do go soft, the fix is a fluid service rather than a cable turn. That job is a brake flush — most people know it as a bleed — and it's $30 per brake. Old fluid absorbs water, water boils on a long descent, and a lever that went firm at the top of the hill goes soft at the bottom. If your brakes feel spongy or the bite point moves around, that's the job you want.

One thing worth knowing for riding around here: long descents load the brakes far harder than flat riding does, and a pad that's fine on errands can be near the backing after a season of the hills between Castle Rock and Sedalia. Pads are cheap. Rotors and rims are not. Checking them is free.

The drivetrain wears as a set, and the order matters. The chain wears first and fastest, because it's the only part where every link is a bearing running in grit. As the pins and bushings wear, each link gets fractionally longer, and the chain no longer sits down in the tooth valleys the way it was cut to.

That matters because a stretched chain reshapes the teeth it runs on. Cassette cogs are the same hardness as the chain and give way first; the chainrings last longer. Replace the chain while it's still within spec and the cassette survives three or four chains. Ride the chain until it skips and you're replacing both, and possibly a chainring.

You can check this yourself without buying anything. Shift into the big chainring, grab a link at the front of the ring, and pull it away from the teeth. If you can lift it far enough to see daylight under a whole tooth, the chain is finished. A $12 chain checker from any shop is more precise — 0.5% is time to replace, 0.75% means the cassette is probably going with it. I check this on every bike that comes in and I'll tell you where you are on that curve even if you didn't ask.

Shifting quality follows a different curve. Cable and housing collect grit and corrode from the inside, and the symptom is always the same: the derailleur moves fine in one direction — the direction the spring pulls it — and lags in the other. If your shifting is crisp going one way and slow going the other, that's friction, and no amount of barrel adjuster fixes it. New cable and housing does, at $50 plus materials.

Anything not on this list gets looked at first and quoted before work starts. Estimates are free, and there's no charge for telling you the honest answer is "leave it alone for now."

If the brake or shifting complaint turns out to be part of a bigger service due, see bike tune-ups. If a wheel is rubbing or a rotor is rubbing because the wheel is out of true, that's flat tires and wheel service.