From Unofficial Zero Manual
This is a common sound on Zero motorcycles, for reasons which have never been decisively explained.
- Related Confirming Symptoms
- Occurs only when pressing on the brake lever or pedal.
- Vibration felt through the brake lever or pedal when squealing.
- Brake performance seems technically unaffected.
- As the loudest sound from the vehicle, this can be unnerving for rider, passenger, or onlookers.
- Potential Causes
- This was more common on 2013-2014 models which had cheaper / lower spec brake systems.
- This suggests a design issue between the disc and calipers that tends to produce resonance the way the pad is mounted.
- Potentional Solutions
- LocTite Disc Brake Quiet stick applicator for the backs of the pads.
- Apply water to the calipers after a ride seems to eliminate squeal for about a week or so.
- Camfering pad edges.
- If the bike is new and brake squeal is constant:
- Bed the brakes per the OEM manual and then give the bike a gentle wash.