Part 17 in the Diagram.
Standard Replacement Front Master Cylinder for Vespa LX50 / LX125 / S 50 / S 150 (Genuine Piaggio)
This is a Genuine Piaggio replacement part.
This is a direct replacement item for the factory master cylinder on the Vespa LX50 / LX125 / S 50 / S 150. Master cylinders hydraulically compress the brake fluid in the braking system when the lever is squeezed, causing the piston in the caliper to press the pads against the disc and slow the scooter down.
Over time the seals inside the master cylinder start to wear out, and it either fail to release fluid pressure once the lever is released (meaning the brakes stay stuck on) or it fails to compress the fluid (meaning the brakes don’t work, or are reduced in their capacity).
The best way to fix this is to replace the master cylinder all together, and get everything working properly again! Replacement is simple as bolting on and bleeding up. It is recommended to change all the fluid in the system when installing the new master cylinder.