Norton Commando 850 MK3 Genuine Girling Rear Master Cylinder Assembly 1975 PN# 06-5776

The Girling name is a legacy brand that dates back to the 1920s and has long been known for innovation and quality brake parts. A complete new lineup of motorcycle brake components are now available replicating the original equipment as specified for BSA, Norton, and Triumph motorcycles.

The complete Girling rear brake master cylinder assembly is a reproduction of the original Lockheed design, and includes the alloy master cylinder housing, stainless steel master cylinder barrel and pushrod. The master cylinder barrel is fitted to the housing and factory pre-set. Some additional adjustment may be required to achieve optimal performance. The reservoir cup is pre-installed on the master cylinder and is an integrated part of the assembly.

When the brake pedal is operated the piston moves along the bore to displace hydraulic fluid under pressure to operate the caliper pistons. On releasing the brakes, the return spring moves the piston back faster than the fluid can return and this causes the lip of the main rubber cup to relax and fluid passes over the cup from behind, through the holes drilled in the piston head for this purpose. When the piston is fully back against the circlip stop, a small bypass port in front of the main cup is uncovered, releasing all fluid pressure within the cylinder. This port also allows for expansion and contraction of the fluid caused by temperature changes during operation. The check valve at the bottom of the cylinder bore assists in purging air from the system during bleeding by ensuring a fresh charge of fluid each time the piston is stroked.

The assembly is mounted to the right-hand footrest with two bolts. The master cylinder pushrod is threaded into a clevis, which swivels on an extension of the brake pedal. Once all of the plumbing is fitted and sealed, fluid is added to the reservoir cup and the hydraulic system must be bled free of any air. Please refer to the factory workshop manual for detailed instructions.

View or download the Lockheed Hydraulic Brake Equipment Service Instructions