Why is my brake caliper piston sticking and not returning?

3 common reasons:

1. Air bubbles in the brake system. Most calipers work on a hydraulic system which relies on the free-flowing movement of brake fluid to push the pistons out which in turn push the brake pads on to the brake discs, bringing the vehicle to a stop. Air bubbles in the system will inevitably hinder this process and will either makes your brakes feel ‘spongy’ and/or stop the piston from returning to its normal position due to the air being decompressed and the seal cannot exert enough force to push the piston back.

2. Rust caused by dirt and water ingress. If the internal and external seals on the caliper fail (wear and tear overtime, or accidentally torn on fitting, lodging out of position), dirt and water can get to the pistons and the pins causing rust, and overtime, seize. It is important that your replacement calipers are zinc plated to reduce the chances of this happening. Look out for aftermarket suppliers cutting costs by simply spraying the calipers silver to make it look like they’ve been zinc plated.

3. Improper installation / servicing. Replacing calipers is not rocket science, but you’ll be surprised how many people incorrectly install calipers, which can lead to uneven brake pad wear, torn seals leading to earlier deterioration of calipers, not flushing out the brake fluid properly, clamping flexi hose pipes causing the internal pipe to collapse, not building up sufficient pressure in the brake system before connecting the handbrake cable, etc. We provide simple instruction guides with all our calipers for easy fitting and avoiding common mistakes, but we highly recommend following the manufacturer’s maintenance instructions. We find that the Haynes Manual for the relevant vehicle is also very helpful.