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MG MGB Technical - Later tandem type master cylinders

hi,

Does anyone know the diameter of the later tandem brake master cylinder pistons? Also, did the pedal ratio change between this and the single circuit system?

many thanks
ian
Ian Harris

I'm almost certain the pedal ratio did change, as I know the single-circuit without servo needs very little extra pressure compared to when there is a servo (which was only optional), but others have said that when the integral servo fails there is a big difference in pedal effort required.

I don't have the size, but regardless of whether they are the same or different you also need to look at the two pedals, and this is where things get odd. The single-circuit master has its push-rod pushed towards the driver to operate the brakes, whereas the later integral servo seems to have it pushed away. This means the pedal pivot and clevis-pin have to be the other way round, but the Parts Catalogue quotes the same part number.
Paul Hunt 2010

I've just been doing a bit of digging looking at pictures on the b&g website. Maybe I'm going mad but I could have sworn there was a model which had a tandem cylinder and remote servo? ie the cylinder was still the same orientation as the single circuit one.

cheers
ian
Ian Harris

You are quite right Paul - the single circuit master cylinder sits between the pedal and the driver, so the push rod is mounted above the pivot as in this diagram.
http://www.moss-europe.co.uk/Shop/ViewProducts.aspx?PlateIndexID=27
The brake pedal is AHH6153.

On the later dual circuit, the master cylinder is in front of the pedal and so the pedal is quite different as shown here.
http://www.moss-europe.co.uk/Shop/ViewProducts.aspx?PlateIndexID=26
The brake pedal is BHH1890.

I have fitted this set up to my 1969 car and it wasn't straightforward. I had to open up the hole for the pedals to get it to fit. The in-line servo definitely makes quite a difference. If I am pushing the car around without the engine, the pedal effort to stop it rolling down my drive into the street is a fair bit higher than when the servo is operating.



Mike Howlett

Thanks Mike - shows it nicely.

Ian - There was a remote manifold with shuttle-valve for the early North American twin-circuit master, are you thinking of that? Clausager sez no servo for the split system until the integral/direct-acting for NA in 75. The UK continued with the single circuit with optional (standard on V8 and from 73 for 4-cylinder cars) remote master until 77.
Paul Hunt 2010

This thread was discussed between 19/04/2010 and 21/04/2010

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