the rear brake on my 4 pro is squealing really loud every time i use it.

Diagnosis

The loud squealing from your Mi Scooter 4 Pro's rear disc brake is almost always caused by vibration between the pad and rotor. This is typically triggered by contamination (like oil, grease, or road grime on the pads or rotor), a glazed rotor surface, or pads that are worn down or of a low-quality compound.

How to Fix It

Start with a thorough cleaning and de-glazing of the braking surfaces.

1. Securely prop up the scooter so the rear wheel is off the ground.
2. Remove the rear wheel to access the brake caliper and rotor easily.
3. Spray or wipe the metal brake rotor liberally with isopropyl alcohol (90% or higher) using a clean, lint-free cloth. Remove all visible residue.
4. Remove the brake pads from the caliper. Lightly sand their friction surfaces on a flat piece of 120-220 grit sandpaper to remove any glazed, shiny layer.
5. Clean the pads with isopropyl alcohol to remove sanding dust, and give the rotor a final wipe.
6. Reinstall the pads and wheel, ensuring everything is tightened to specification.
7. Bed in the brakes by performing a series of moderate stops from low speed to transfer fresh pad material onto the clean rotor.

If That Didn't Work

If the squeal persists, the pads are likely too contaminated or are worn beyond their limit. Replace them with a set of high-quality, sintered metal brake pads specifically for your scooter model. Also inspect the brake rotor for deep grooves or warping; a bent rotor can cause consistent noise and may need replacement. Finally, ensure the caliper is aligned correctly so the pads contact the rotor evenly.

Heads Up

A squealing brake often indicates reduced stopping power. Always test your brakes cautiously at low speed in a safe, flat area after any maintenance. Avoid using standard household cleaners or lubricants near the brake system, as they can cause permanent contamination.