After long or hard braking, for example down a long hill or in stop-start traffic with a heavy load, the brakes get weaker. There are two kinds. Fluid fade: the lever goes soft and travels further, because old brake fluid with water in it boils and makes vapour bubbles. Friction fade: the lever stays firm but the bike does not slow, because overheated pads or shoes lose grip. Drum brakes also fade because a hot drum expands away from the shoes.
Is it safe to ride?
When it happens, stop as soon as it is safe, and let the brakes cool for several minutes. Do not ride on until the cause is fixed, because it will happen again on the next hill.
Quick checks first
- After cooling, does the lever feel normal again?
- Look at the fluid colour: dark brown?
- Spin each wheel after cooling: does one drag?
- Do you hold the brake on for long periods instead of using lower gears on hills?
Diagnose it step by step
1When the brakes faded, did the lever or pedal go soft and travel further?
- Yes: fluid fade. Go to step 2.
- No, it stayed firm: friction fade. Go to step 4.
2Is the fluid dark, or has it not been changed within your manual's interval?
- Yes: Replace brake fluid and bleed the brakes with new fluid of the type on the cap (K-Light 125: DOT4). Old fluid boils at a much lower temperature.
- No: go to step 3.
3Does a brake drag, so it heats up even when you are not braking?
- Yes: go to Brake drags and the wheel does not spin freely.
- No: there may be air in the system. Bleed it; if it still fades, the wrong fluid may be in the system. Have a workshop flush it.
4Is it a drum brake?
- Yes: drums fade more than discs. Check the shoes for glazing and the drum for blue heat marks with Service a drum brake. Use engine braking on hills.
- No: go to step 5.
5Are the pads glazed, or of an unknown or very cheap make?
- Yes: Replace disc brake pads with pads listed for your bike.
- No: go to step 6.
6Is the disc blue, glazed, or near its thickness limit?
- Yes: a thin disc holds less heat. Check a brake disc.
- No: check riding: change down a gear on long hills so the engine helps, and use both brakes firmly in short applications instead of dragging one.
Causes, most likely first
| Cause | How to confirm | Fix |
|---|---|---|
| Old fluid with water in it | Soft lever when hot; dark fluid | Replace brake fluid and bleed the brakes |
| Dragging brake | Wheel hard to spin; hot disc after easy ride | Check for brake drag |
| Holding brakes on long hills | Happens only on descents | Use lower gear, brake in firm short bursts |
| Glazed or poor pads or shoes | Shiny surface; firm lever but weak | New pads or shoes |
| Thin or glazed disc | Below limit, blue | Check a brake disc |
| Hot drum expanding | Drum brake, long descent | Engine braking; check shoes and drum |