How to Fix Bike Brakes That Don't Work

Start with the lever, not the tools. Pull each one slowly and feel where it stops. That single squeeze tells you most of what's wrong.

Three feels, three verdicts. A lever that sails all the way to the bar means no tension is reaching the pads — a stretched cable, worn pads, or, on a hydraulic, air in the line. A lever that stops firm but the bike still won't slow means the pads are touching but not gripping, which is almost always glazing or contamination. A lever that grips but screams or shudders is an alignment problem, not a power problem.

• ▸Sails to the bar → cable, pads, or a hydraulic bleed
• ▸Firm but weak → glazed or greasy pads
• ▸Grips but squeals or judders → toe-in or a dirty braking surface

Safety first: on a hydraulic disc brake, a lever that pulls to the bar with zero resistance means there's no hydraulic pressure at all. Don't ride it, even to the shop.

Rim pads are a consumable. New ones carry 4 to 5mm of rubber with wear grooves moulded into the face. Once those grooves are gone, or you're down to roughly a millimetre of rubber above the metal shoe, they're finished. Swap them.

Weak-but-not-worn pads are usually glazed — a hard, shiny skin baked onto the surface. Scuff it off with coarse sandpaper, 80-grit, until you see fresh matte rubber underneath. While you're there, dig out any embedded metal slivers or grit; those score the rim and eat braking power.

Cheap new pads are a genuine upgrade if yours have gone old and hard. Salmon-coloured compounds bite noticeably better in the wet than the standard black ones.

If the rim sidewall has a hollow or a visible groove worn into it, the rim itself is spent — new pads won't save it, and a sidewall that blows out at speed is dangerous. That's a wheel job, not a pad job.

A pad only works where it lands. It has to hit the flat braking track of the rim square-on — not the tyre above it, not thin air below it.

Set the top edge of the pad about a millimetre below the top edge of the rim. Too high and it grabs the tyre sidewall and can peel it off the bead. Too low and it dives under the rim into the spokes as it wears. Loosen the pad's eyebolt, hold the pad flush against the rim, and tighten.

With the lever released you want roughly 1 to 2mm of gap on each side, even both sides. A pad resting on the rim drags and robs speed; a pad parked miles away wastes half your lever throw before it does anything.

Cables stretch and housing settles, especially in the first month on a new bike. The pads drift away from the rim and the lever starts kissing the bar. You're clawing that lost distance back.

Small adjustment: the barrel adjuster where the cable enters the lever or caliper. Turn it out — anticlockwise, away from the body — to pull the pads closer. Quarter-turns, checking after each.

Big adjustment: undo the pinch bolt at the caliper, hold the pads against the rim (a helper or a toe-strap works), pull the cable snug with pliers, and retorque the bolt, around 6 to 8Nm. Now you've got the full range of the barrel adjuster back for fine tuning.

Target feel: a firm stop with a third to half the lever travel still in reserve. If you can squeeze the lever to the grip, there isn't enough tension yet — keep going.

Squealing rim brakes almost always want toe-in. That means the leading edge of the pad touches the rim a fraction before the trailing edge — about a millimetre of angle across the pad.

The old shop trick still works best. Fold a business card over the trailing edge of the pad, hold the pad against the rim so the card sets that gap, and tighten the eyebolt. Pull the card out. The pad now bites leading-edge-first, which stops the vibration behind the howl and gives a smoother, stronger grab.

Modern dual-pivot calipers with cartridge pads often run fine dead flat. But if yours sing, toe them in — it costs nothing and takes two minutes.

Disc pads hide inside the caliper, so people forget them until they're metal-on-metal. Pull the wheel and look. Replace the pads once the friction material is thinner than about 0.5mm — that's the compound only, not counting the metal backing plate behind it.

Check the rotor while the wheel's out. A new rotor is roughly 1.8mm thick. The minimum is stamped right on it: "MIN.TH 1.5" on most Shimano rotors, 1.55mm on SRAM. Under that figure it needs replacing — a too-thin rotor flexes, overheats, and can crack.

If you've been riding on pads that were already gone, a grinding scrape means the backing plate has been chewing the rotor. Inspect it closely before you assume fresh pads alone will fix things.

This is the number-one reason a disc brake suddenly goes gutless. One drop of chain lube, a mist of degreaser, or a smear of brake fluid on the rotor or pads and the power falls off a cliff, often with a loud glassy squeal to go with it.

Clean the rotor first, because it's easy. Wipe it down with isopropyl alcohol, 90% or stronger, on a clean lint-free rag. Never reach for a petroleum solvent or an oily workshop rag — you'll just spread the problem around.

Pads are harder. Lightly contaminated pads can sometimes be saved: sand the surface back to clean material with fine sandpaper, then burn off the residue with a heat gun or a quick pass of a torch until they stop smoking. Pads that are properly soaked — anything that met DOT fluid or oil — are done. Bin them and fit new ones.

Handle rotors and pads by the edges. The oil off your fingertips is enough to contaminate a fresh pad before it's even bedded in.

A steady tick-tick-tick as the wheel spins is the rotor grazing a pad. Usually the caliper is just sitting slightly off-centre over the rotor.

Loosen the two caliper mounting bolts about half a turn each so the caliper can float on its mount. Squeeze the brake lever hard and hold it — that pulls the caliper square onto the rotor. Keeping the lever squeezed, tighten both bolts evenly. Release, spin the wheel, and sight the gap against a light background.

Still rubbing in one spot per revolution? The rotor's bent. Watch for where it kisses the pad to find the high spot, then ease it straight with a rotor truing fork — an adjustable wrench does in a pinch. Small nudges only. Steel remembers what you did to it.

Two different worlds here, so know which disc brake you own. Hydraulic brakes have a sealed fluid line and no cable. Mechanical, cable-actuated discs pull a wire, exactly like a rim brake.

Hydraulic, and the lever feels soft or pulls close to the bar with good pads fitted? There's air in the system or the fluid has gone off — it needs bleeding. Use the correct fluid and never mix types. Shimano, Tektro and Magura run mineral oil; SRAM, Hayes and Hope run DOT. Some brands (Formula, for one) use mineral oil on some models and DOT on others, so don't go by badge alone — confirm the fluid against the marking on the reservoir cap or your brake's manual before you open anything. Put DOT in a mineral system, or the reverse, and it swells and destroys the seals. A home bleed kit is cheap; if you're unsure, a shop bleed runs about £20 to £35.

Mechanical disc? There's nothing to bleed. Take up the cable slack at the barrel adjuster just like a rim brake, and set the inboard fixed pad with its adjuster so it sits around half a millimetre off the rotor.

Never mix mineral oil and DOT fluid, and never crack open a hydraulic system without the right bleed kit for your brand. Getting air in is easy. Getting it back out is not.

Fresh pads, rim or disc, feel weak until they're bedded in. There's no even layer of pad material on the braking surface yet, so the first few stops are all bark and little bite.

Find a quiet stretch. Ride up to about 25 to 30km/h and brake firmly down to walking pace without fully locking the wheel, then repeat that 20 to 30 times. It lays down a smooth, even transfer layer and wakes the brakes up. Do it before your first real ride, not halfway down the first hill.

Test at walking pace in a safe spot before you commit to traffic or a descent. If the lever still pulls to the bar or the bike won't stop, go back to the top and start again — you've missed something, and brakes aren't the place to guess.