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MG MGB Technical - Clutch Master Cylinder problems

Really need some help on this one. I rebuilt the clutch master cylinder. (67 GT with the line on the master cylinder). According to moss and a paper that came with the rebuild kit, I have the correct kit for this unit.

Bore is perfecty smooth, No pitting or andy corrosion.

When I try the unit. The piston sticks to the rear. This only happens with fluid in the unit.

Couple of questions. What way should the dished washer face? I put the back (by the pushrod) rubber piston on with the double lip going in towards the resevior. Spring is good.

Any help is appreciated. I am getting tired of taking the unit out.
Bruce Cunha

Did you use the special grease provided? Maybe you can stuff some (or some more) in behind the boot.


If I understand you correctly, the piston is positioning towards the rubber boot when you try the unit with fluid in it. If this is without the pushrod connected to the fork I would expect that based on the piston being driven by the cup spring.

Your dished washer I take to be the piston cup. This should have its back to the piston and the lip side facing the spring.

The double lip of the boot should face into the body, as you say yours does, ie towards the piston. The inner clip holds this in tension against the push rod.

From the rear moving foreward there should be, in order:

1 pushrod extending through the

2 boot, held by internal and external clips

3 piston

4 piston cup (your dished washer

5 pistin cup filler, though I don't recall this specific part in my slave. Guess it must have been there - I'm doing this from the manual diagram

6 spring, mounted broader diam against the rear of the body of the unit.

Hope this helps
Regards Roger
Roger T

Thanks Roger.

Looks like I have everything as it should be. I do note wear on one side of the piston (black normal color is worn to shiny) so this could be that it is enough slact to bind the piston back in the housing.

After playing with this for too many times, i decided I would just buy a new one. Not something that should wear out in my lifetime and probably a safer approach.
Bruce Cunha

Apologies. Revisiting, I realise I confused your two Clutch system problems and have managed a response based on the slave cylinder here where your problem was with the master.

Late night posts - need to note for future!

Roger T

This thread was discussed between 29/08/2005 and 31/08/2005

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