Dual Brake Plumbing

1977 and later RHD dual system with combined master cylinder, servo and balance switch. The primary circuit is closest to the driver and individual ports are plumbed to the calipers. The secondary circuit is furthest from the driver and goes to the rear brakes: (Haynes 1989 edition)

Incidentally there does not appear to be a joint in the rear pipe, as shown by Haynes.

Port arrangement on the above master cylinder of an RHD car: (John Maguire in Australia)

Early LHD dual system with separate master cylinder and balance switch. The primary circuit is towards the front of the master cylinder i.e. furthest from the driver, is plumbed to the front of the balance switch, and individual ports go to the calipers. The secondary circuit is closer to the driver, is plumbed to the rear of the balance switch, and goes to the rear brakes.

Later LHD dual system with combined master cylinder, servo and balance switch. The primary circuit is closest to the driver and individual ports are plumbed to the calipers. The secondary circuit is furthest from the driver and goes to the rear brakes. Used on both right- and left-hand drive cars: (Haynes)

Justalad posted this on the MGOC forum from the 1978 Repair Operation Manual AKM4070 which clearly shows and describes how the pipes connect to the ports ... or is it? Step 3 says 'Disconnect the secondary feed pipe', but shows it positioned and angled for the lower rear (primary) port. Step 4 says 'Disconnect the primary feed pipes ... a Left-hand brake b Right-hand brake' showing 4a positioned for the upper rear (primary) port but shows 4b going to the front (secondary) port. So the drawing has the labelling for pipes 3 and 4b reversed:

The September 76 Parts Catalogue is even worse as it shows the right front Teed with the rear (red arrow) with some other component piped (2) to the 3rd port on the master: (Leyland Parts Catalogue)

I subsequently obtained copies of both the 1978 Repair Operation Manual AKM4070 and the 1977 LHD Workshop Manual AKD3524 section on master cylinder removal which has the same drawing and description. These drawings indicate two of the pipes going up and one down. Indications such as this can't be taken as gospel, although one should be able to believe the words and the labelling are correct. Clausager shows an RHD with this braking system with one pipe going up and two down, which would be logical, with the one going across to the left-hand caliper and the other two going down to the right-hand caliper and the rear, without being able to tell which is which. Clausager doesn't show how the left-hand caliper pipe goes across but this picture does - over the heater (which is how rubber bumper remote servo pipes were routed):

For LHD cars to avoid the pipes crossing over it would be logical if the left-hand caliper pipe went down, and the right-hand caliper and the rear pipe go up and across the heater in the other direction, then down to the caliper and under the floor. This would make the pipe orientation on the drawings correct for an LHD car, and 4b correctly in the upper port, but the labelling of 3 and 4a is still reversed. Kelvin Dodd of Moss Motors in the US has access to a 1979 LHD LE with only 40 miles on the clock and unmolested, and he confirms that both calipers go to the primary ports and the rear circuit to the secondary port.

And both the Leyland AKM manuals have the full plumbing layout on an earlier page which do show that the calipers are connected to the primary circuit and the rears to the secondary. From the LHD perspective though as the right-hand is shown connected above the left-hand, on an RHD they would be reversed: