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Brakes - wheel and master cylinder information

Wheel cylinder bore diameters

0.75in Bore Notes 0.75in Bore Notes 0.6875in Bore Notes
Mini '59 Dry suspension, to chas# As7 359770 MK II And derivatives, single line to '77 1275 GT Single line chas# 19416-21569A (1974-76)
997 Cooper To Austin chas# C-A2S7 382831 "S" MKII With servo 1275 GT Diagonal split chas# 19416-21569(1974-76)
997 Cooper To Morris chas# K-A2S4 382183 "S" MKIII Innocenti (1275GT not UK) Front to rear, 10in wheels
1275GT Front to rear tandem brakes (metric fitting) '78 on 1275 GT With servo, 10in wheels "S" MKIII export
850/998/1100 Front to rear (benelux countries), pre '75 (belgium build) 0.5625in Bore Notes 0.625in Bore Notes
850/998 Front to rear October '78 on ('80-'84 Europe) 850/998 Diagonal split (NOT UK) Norway/Japan Mini 59 Dry suspension, from chassis number A2S7 359770
Van/Pickup Diagonal split (metric fittings) '77 on 850/998 diagonal split execept van/pickup (1977-78 (1976-79 europe) MKI All hydrolastic, from Sep '64 on
998 Front to rear brake system (metric fittings) '84 on ERA turbo 997 Cooper Austin chas# C-A2S7 382832 on
998/1300 latest '90 Mini with built in servo 0.500in Bore Notes 997 Cooper Morris K-A2S4 382184 on
Minis from 1990 onwards should be 0.75 inch bore. (GWC 1102) info from Peter Kay 28 12 02 1275 GT Single in line brakes CHAS# 21570A on ('76-'77) "S" MKI With servo
1275 GT Diagonal split (metric fittings) chas# 30001 on ('77-'78)
850/988 Diagonal split (NOT UK) Europe '76-'77

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Lockheed part numbers for wheel cylinders

Models and notes Part number Diameter (in)
Mini MKI 1959-64 Austin 359770 Morris 170653 4241-239 3/4
Mini MKI 1959-64 Aaustin 358923 Morris 170654 4241-015 5/8
Mini MKI 1964-67 Riley 1963-67 4241-015 5/8
Mini MKII 1967-on, Clubman 1969-on, Riley MKI 1961-63, Riley 1967-69 4241-239 3/4
Mini Canadian market 4241-140 11/16
Mini 1275 GT 1969-on, Moke 1964-68, Cooper MKI, II, III 4241-015 5/8

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Wheel cylinder - changing

To supplement the information found in Haynes and other manuals, here's John Bullas' method:

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Master cylinder - suitability for disc brake use

If you have twin circuit brakes then the master cylinder is OK for disc use. The post '84 cars don't have the same master cylinder as post 74 drum braked cars, but it IS functionally equivalent.

Once the 8.4 inch discs came in after '84, BL discontinued the old master cylinder as a spare part meaning that if you replace a pre '84 master cylinder you need to replace the two pipes from the master, and also the wiring. The new cylinder doesn't have a PDWA, just a fluid level warning. The new one is identified by a yellow band around it.

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Cooper S master cylinders

The old-style brake master cylinder (twin of the clutch master cylinder) is perfectly capable of being used with Cooper S disc brakes.

The brake master cylinder fitted to Cooper S models was taller, holding more fluid. Supposedly in heavy competition, the extra brake fluid capacity was needed in a Cooper S to account for the large fluid displacement as brand new brake pads became completely worn out over the course of a single event. This is not a concern with today's brake pads as used on the road. It's the responsibility of owners of any Cooper S disc-equipped Mini to regularly check the fluid level over the (very long) life of the brake pads.

It is also thought that all 10 inch wheel 1275 GTs went out with single circuit brakes and the larger tin can. One good move on either of these older master cylinders is to fit the screw-in transparent extensions. You can see the levels any time you open the bonnet without the unscrew and peer hassle.

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Footer SSI Insert revised: 23-Feb-2016

07 May 2003