Rear brake cylinder sizes

Comparison of wheel cylinder sizes.

Lockheed rear wheel brake cylinder, twin piston comparison as found on BMC rear axles [Midget, Sprite, Austin A40] and Mini rear. Fixed cylinder, one per side.

Cylinder bore	Unipart part number	AP Caparo part number	Old Lockheed part number	Notes on original applications (not an exhaustive list; approx years)
1/2" (0.5)	GWC1126			Mini 1275GT rear - 1975 to 1976.
5/8 (0.625)	GWC1101	4241-075P	LW11075	Mini Mk1 Cooper S with servo; rear. Mini MkI (not Cooper or Cooper S) rear - 1962 to 1967
9/16" (0.563)	GWC1131			Mini MkI rear - 1959 to 1967
9/16" (0.563)	GWC1134			Mini MkIII rear - 1974 to 1978
11/16" (0.689)	GWC1129	4241-193P	LW11193	MG Midget [1500] rear - 1975 to 1979. Mini 1275GT rear - 1964 to 1975.
3/4" (0.75)	GWC1102	4241-396P	LW11396	Austin Healey Sprite & MG Midget (1098 & 1275 engines) rear, 1964 to 1975. Austin A40 Mk2, rear - 1962 to 1968. Mini MkI (not Cooper or Cooper S) rear - 1959 to 1962. Mini MkII (not Cooper or Cooper S) rear - 1967 to 1975 plus other Minis
7/8" (0.875)	GWC1115	4241-933P	LW10104	1962 MG Midget Mk1 & Austin Healey Sprite MkII rear (with front drum brakes and twin piston fixed single rear wheel brake cylinders). NB earlier cars have sliding single piston wheel cylinder of 7/8" bore in a different back-plate.

NB position of locating pin and matching hole in original rear brake back-plate may vary, so might need to drill different locating pin hole in rear brake back-plate if considering changing sizes of wheel cylinder outside original application.

Note early Austin Healey Sprite and MG Midgets (until approx late 1962) as well as Morris Minors had a different style wheel cylinder (single piston, sliding), rather than the above fixed cylinders with dual pistons..

Would MGB wheel cylinders GWC1103 (7/8" [0.875]) - MGB GT and MGB Roadster GWC1122 (13/16"? 31/64? [0.8?]) fit any of the above rear back-plates?