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 completely new lineup of motorcycle brake components is now available replicating the original equipment as specified for BSA, Norton, and Triumph motorcycles.
The master cylinder reservoir diaphragm is a thin rubber cup that is designed to displace air in the reservoir cup once the hydraulic fluid is topped up to the correct level. It also forms a seal under the reservoir cap, preventing contamination of the fluid. Genuine Girling quality.
The diaphragm sits under the reservoir cap and is sealed with a thin paper gasket fitted under the cap.
The diaphragm is of the telescopic design and must be correctly formed when fitting to the underside of the cap during installation. As fluid levels vary during the bleeding and operation of the hydraulic brake system, the diaphragm changes its shape slightly to displace air in the reservoir cup.