You have to push the rear brake pedal a long way down before the brake works, or it reaches the footpeg or its stop. On a drum brake this is usually adjustment or worn shoes. On a hydraulic (disc) rear brake it suggests air, a low fluid level, a worn master cylinder, or the pedal and pushrod set wrongly.
Is it safe to ride?
No, until the pedal works within its normal travel. This is usually a quick fix.
Quick checks first
- Measure the free play at the pedal pad (K-Light 125: 20 to 30 mm).
- Drum brake: look at the wear indicator pointer.
- Hydraulic brake: check the rear reservoir (and CBS reservoir) level.
- Has the chain or rear wheel just been adjusted?
Diagnose it step by step
1Is the rear brake a drum (rod or cable) or a disc (hydraulic)?
- Drum: go to step 2.
- Disc: go to step 4.
2Drum: does turning the adjuster in bring the free play back to the manual value?
- Yes: Adjust a drum brake. Check the brake light after adjusting.
- No, the adjuster is at its end: go to step 3.
3Is the wear pointer past its mark, or the brake arm past a right angle when applied?
- Yes: worn shoes or drum. Service a drum brake.
- No: the cam or arm may have been refitted on the wrong spline. Check during the service.
4Disc: is the fluid level above LOWER in the rear (and CBS) reservoir?
- No: check pads with Check brake pad wear and look for leaks. See Brake fluid is leaking.
- Yes: go to step 5.
5Is the pedal free play too large because the pushrod or stop bolt is set wrong?
- Yes: Adjust the rear brake pedal. On the K-Light 125, the pushrod should leave 0 to 0.2 mm gap at the piston and the pedal free play should be 20 to 30 mm.
- No: go to step 6.
6Does the pedal feel soft, or sink when held?
- Soft: air. Replace brake fluid and bleed the brakes; on a CBS bike use Check a combined braking system (CBS).
- Sinks: Check the brake master cylinder, and on CBS bikes the CBS internal leak test.
7Is the pedal bent, or its pivot worn so it moves sideways?
Causes, most likely first
| Cause | How to confirm | Fix |
|---|---|---|
| Drum brake needs adjustment | Large free play; adjuster has thread left | Adjust a drum brake |
| Worn drum shoes | Pointer past mark | Service a drum brake |
| Pedal or pushrod set wrong | Free play outside manual range | Adjust the rear brake pedal |
| Air or low fluid (disc) | Soft pedal; low reservoir | Replace brake fluid and bleed the brakes |
| Worn master cylinder or CBS leak | Pedal sinks when held | Check the brake master cylinder |
Reference values (K-Light 125)
| Item | Value | Source |
|---|---|---|
| Rear pedal free play | 20 to 30 mm | K-Light 125 manual, PDF p. 49 and 62 |
| Pushrod to rear master piston clearance | 0 to 0.2 mm | K-Light 125 manual, PDF p. 116 |