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MG MGB Technical - Dual circuit brake master cylinder

I have an early chrome bumper GT, and while rebuilding the car I've decided to fit the later dual circuit braking system with a servo. I have rebuilt the cylinder but the brake failure switch broke off when I tried to remove it.

I got the remainder of the switch out, and as I'm not too bothered about having the switch, I have replaced it with a short bolt to act as a blanking plug, and have used a copper sealing washer. I take it this will not cause any problems?

I will be fitting new brakes pipes shortly and need to check where they go, as I have only dealt with single circuit brakes. As I see it, the union as the very end of the cylnder goes to the rear, and the other two in-line unions are for the front - does it matter which goes to the left and which to the right?

Many thanks

Paul Grundy


As you probably know the switch is activated by a presure difference between the 2 circuits. Such a difference being normally due to leak. Replacing the switch with a bolt means you only get half the advantage of dual circuit. Having said that it is what I did on my dual but no servo system when I had a fluid leak through the switch.

You are correct about the pipe unions.

When rebuilding your master cylinder did you change the seals on the wasted shutle that operates the warning switch. If so how did you get it out to do so.

I have had a half rebuilt servo master cylinder on the bench for a year or more because I can't get the shutle out.

David Witham

This thread was discussed between 15/10/2004 and 18/10/2004

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