Clutch Master Cylinder Cap
Le Mans Master
Joined: Sep 2003
Posts: 8,847
Likes: 795
From: Longview Texas
The hole is a vent to allow air behind the diaphragm inside the reservoir as the fluid level drops so a vacuum is not created. The rubber diaphragm is designed to expand downward as the level drops so air is not drawn in on the fluid side.
Yes, you need the hole.
Yes, you need the hole.
