I believe the reason for the dual master cylinder in the so-equipped
MGB is that the car has disc brakes in front and drum brakes in the
rear. This necessitates a different size piston in the master for each
type braking circuit.
That being said, I agree that each circuit should have a firm pedal.
My take on the OP's problem is that the rear circuit was clogged up
and the front circuit wasn't fully bled.
CR
Paul Hunt wrote:
> My subsequent thoughts also. As I say I have no experience of dual
> circuit brakes with one circuit failed, but logic dictates that surely
> the whole point of the system is that if one circuit is leaking and not
> developing any pressure, or is full of air, the other circuit *must*
> give a firm pedal albeit it with increased stopping distances
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