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MG MGB Technical - Clutch master cylinder.


I'm rebuilding pedal box etc and have a clutch master cylinder that does work. However, I can see a small nick at the base of the round cylinder that could easily develop into a future problem.

How can I repair it? Solder? Metal 'filler'?


Iwan Jones

Whereabouts..I think a picture is in order. If it ain't broke springs to mind. if it doesn't leak now then it's pretty unlikely to do so in the future. A good clean & paint to protect the exterior, the interior is usually full of fluid so is unlikely to corrode through.
P M Gregory


Thanks for the reply. It is at the base of the cylinder/reservoir. Sorry no camera at the mo.

Unfortunately it is a small puncture about 3mm long by 1mm wide at its widest. Is there any way of repairing this
Iwan Jones

You could solder the hole but would need to ensure that all traces of flux were cleaned out. Quite frankly I would fit a new cylinder
Iain MacKintosh

Are you sure that isn't the bypass passage from the reservoir to the cylinder? On top of the cylinder a little way down (see attached)? That is uncovered and on the high-pressure side of the main seal when the pedal is released, and allows fluid to flow from the reservoir though the system when bleeding other than with the pedal. It also allows fluid expansion when it gets hot to be vented back into the reservoir, if it couldn't do that it would apply pressure to the release bearing and tend to cause slip, or cause the brakes to drag in the case of the brake master. When the pedal is operated it's only when the main seal is past the bypass passage that any pressure is applied to the fluid.

Paul Hunt


Thanks Paul, but it is a hole in the round base of the continuation cylinder - if you know what I mean.
Iwan Jones

Could get a stainless steel sleeve inserted? e.g. at Past Parts Ltd or Contract Auto Engineering Ltd. Find them on Google.
Richard Evans

" if you know what I mean."

Sorry, but no :o)

I'm only aware of the one cylinder in the master, and whilst that has the potential for being sleeved, the sleeve would have to extend the full length of the bore, which would block off the bypass passage unless you drilled a hole in the sleeve in exactly the right place.

It just doesn't seem worth it, unless originality is your aim, the present replacements (that I'm aware of) having the translucent reservoir instead of the metal one.
Paul Hunt

This thread was discussed between 23/10/2014 and 29/10/2014

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