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MG MGB Technical - Dual Line Brakes

Does anybody have any experience or know anybody who has experience of fitting some kind of double circuit brakes to an early-ish MGB?

I've got a 1970 GT and would like dual circuit brakes. I know that single line brakes work okay, but dual circuit gives an extra margin of safety.

I cannot fit a later dual line with servo because I think it will foul the wiring on the inner wing.

I have seen US-spec dual line systems but I cannot find any for sale. And anyway, I've seen just the pressure switch assembly for sale on LBC for $375 and that doesn't even include the switch! So goodness only knows how much a master cylinder would cost!

I'm sure that there are some racers running two master cylinders in a modified pedal box.

Any ideas anyone please?



Neil. The 68-74 1/2 North American specification master cylinder is available from Moss US at $209.95. The four way union is expensive, but available, used, from several sources. My only question would be whether you could use the pedal box from your car or would need a NA spec pedal box. I do not think they were "handed", but they might be.

I have picked up two new later model master cylinders for less than Moss is selling them for. Do not know if the people I dealt with can ship internationally, but can check if you are interested. They can supply a used "Switch and Body Assembly" and, if you need it, a pedal box.

Les Bengtson

It is up to personal preference but you can run without the pressure switch assy. All it does is turn on a light on the dash if there is a loss of pressure in one half of the brake system. When this happens your pedal height will drop when applying the brakes. You will know by the feel of the pedal that you lost one circut.
John H

It's a lot of trouble to go to. Whilst it does isolate the rear section if that should fail, if the problem is with the fronts then you still have virtually no brakes.
Paul Hunt 2

Neil, I have a '74 US spec CB mgb roadster. It had the system Les describes.

The US master will fit a UK pedal box. However it uses the cover which has the mechanical brake light switch.

Given your interest is based on safety I should tell you that:-
a) the related junction block and balance switch is prone to leaking around the switch.
b) the US spec master is an real pain to rebuild with new seals etc.
These factors may offset the advantage of dual circuit.

In addition when you place the US master on the RH side of the car the pipe unions on the master are very difficult to get at. In my RHD conversion I have used a normal single circuit master.

You may get much of the additional safety you want by fitting one of the fuid level warning systems that are now available.
David Witham

This thread was discussed between 08/10/2007 and 09/10/2007

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