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MG MGA - Master cylinder

I have just refurbished my master cylinder because of problems I was having with poor brake pressure, replacing all the rubber cups, washers and gaskets. The good news is that the brakes are working well again, but sadly the clutch pressure has completely gone. I've definitely got fluid coming through the pipe into the slave cylinder and I'm pretty sure there's no air in the system, but the pedal hits the floor just as the clutch starts to disengage.
I've just taken the front cover plate off the master cylinder and found that the clutch piston is stopping about 1cm short of the plate, whereas the brake piston is flush with the end of the unit. I then pulled the piston out to see if there was any obvious problem with it, or the secondary cup, but both seem fine ... although I was surprised to find that there was a lot of fluid in that part of the cylinder, between the master cup and secondary cup. Is that how it should be or is fluid leaking past the master cup under pressure?
I suspect I'm heading for a new MC, but before getting out my credit card is there anything else anybody can suggest?
Thanks
Robert Sinclair

Robert
I have just replaced my master cylinder.
I don't know too much about the inner workings, but no doubt someone will be along to advise.
But in the meantime, are you certain there is no air in the slave? The only way I could clear the air was by pressing in the slave piston by hand from underneath. It released a lot of air. I then bled in the normal way, using my better half pumping the pedal, but while I continued to hold the piston in.
If you do go for a new one, I would recommend you don't go for the cheaper TRW one. I had one I'd bought a few years back, and it didn't release the pressure on the discs when the pedal returned (assuming you have discs). I then bought the AP Caparo from Bob West and all was good.

Good luck , Graham
Graham V

Robert
Have you read this?
http://mgaguru.com/mgtech/hydraulics/ht118.htm

Regards, Graham
Graham V

Thanks Graham. I thought I had found and read everything there was about master cylinders on Barney's site, but I missed this one. It sounds like my master cup isn't doing its job properly, despite being new, so the problem must be pitting in the clutch bore, which is probably no surprise after 61 years! I think I'll be buying a new one and seeing if anybody wants the old one to sleeve and rebuild properly (which is too much of a challenge for me).
Robert Sinclair

On my recent trip to Croatia I had clutch problems. Taking the MC apart I found that the secondary seal had come out of its groove and was floating free on the waist of the piston. Putting it back where it belonged cured the problem, I didn't even have to bleed anything afterwards. This was a new AP cylinder fitted last year......
Dominic Clancy

This thread was discussed between 14/07/2017 and 16/07/2017

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