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MG Midget and Sprite Technical - Frog master cylinder


currently overhauling my master cylinder and I have eventually freed the final piston and additional gubbings...

Question - the many books and parts list seem to indicate that the secondary cup sits behind the boot fixing plate and in-front of the actual piston. In the attached picture (red circles) mine seems to have a seal / boot on the actual piston shaft, it actually locates on the step just down from the end of the piston. Can anyone shed any light on this - ie are mine just wrong? do the replacements come in a different arrangement?

The yellow circles are highlighting the main boot on both pistons. I'm assuming these should both be the same size? one of mine looks quite a bit bigger and is less "stiff" than the other. Im assuming this is just aged rubber and they should in fact be the same? Slipped in a second question there.


a reid

Hi Alan are both the bores the same size? In the photo one of the pistons looks bigger?
Bob Beaumont

Hi Bob, think that's down to my lack of photography skills, both pistons are the same diameter and the bores are original - no sleeve.
a reid

Your photos look correct to me. To the best of my recollection my frogeye master cylinder has the seals in the same positions.
Simon Wood

Thanks Simon - so to replace they just need a really good stretching to get them over the piston end?
a reid

Yes they are tight. Plenty of brake fluid as lubricant will help.
Simon Wood

This thread was discussed between 02/11/2015 and 03/11/2015

MG Midget and Sprite Technical index

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