Article: Master Cylinder Identification Guidelines
Posted on 1st December 2011
This original article was previously published by Seven Enterprises in our Autumn 2011 mailer.
Master Cylinder Identification Guidelines
by Mike Kearney
Seven’s Service Shop Manager
Identification of the master cylinders is a common problem that Mini owners encounter when working on an older car or when building a “basket-case” from parts of unknown origin. It really is not too difficult; here is a list of facts to check to minimize the guesswork.
If you have a basket-case car and need to identify which cylinder is the clutch, hold the master cylinder vertically so the filler cap is towards you and the outlet neck is away from you. If it is a clutch master, the pointy end of the mounting flange will be aiming back at you. The centerline of the two mounting bolt holes will be roughly, but not exactly, parallel with the centerline of an imaginary line drawn through the centers of the filler hole and outlet neck. Any master cylinder not passing this test will be a brake master cylinder. One other easy identification is that if you have the large reservoir Cooper S brake master cylinder, the tank will measure 3” exactly from top to bottom of the reservoir. Heritage has recently reproduced the large reservoir Cooper S brake master cylinder in a gold/cad finish vs. the original grey.
Clutch Master Cylinders
- All Minis have 0.75” bore clutch masters. See “identification” above.
- New clutch master cylinders are available in the original metal tank design, as well as two (2) types of improved plastic tank versions.
Single-Line Brake Master Cylinders
Minis with single circuit brake systems originally came in three bore diameters: 0.625”, 0.70” and 0.75”. Bear in mind, the master cylinder should match the type of brakes now on the car for safety and reliable performance as follows:
Dual-Line Brake Master Cylinders
These can be grouped into three categories, “Round Reservoir”, “Square Reservoir”, or “Horizontal”. These feature separate brake line systems so that if one cylinder or caliper fails you still have partial braking.
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