Dual Brake Plumbing

Unboosted   Boosted

Unboosted:

Early (unboosted) LHD dual system with separate master cylinder and balance switch. The primary circuit is nearest the pushrod and feeds the front brakes via the balance switch assembly with individual ports for the two calipers. The secondary circuit is furthest from the push-rod and goes via the balance switch assembly and a single port to the rear brakes. I have adapted the drawing from the one at Moss.com by adding the pedal for clarity:

The WSM is of no help as it doesn't even indicate which is the primary circuit and which is the secondary, but going by the item labelling it could be construed that the lower numbers as represent the primary circuit whereas in fact they are the secondary:

Haynes is slightly better in that although it uses the same numbering it does indicate which is 'primary' and which 'secondary':

The remote pressure failure switch assembly 13H5905: (Somerford Mini)

Internals from Moss Motors:

Boosted:

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. The lower primary port goes to the caliper on the same side of the car as the master cylinder. The upper port goes to the caliper on the other side of the car, over the heater: (Haynes 1989 edition)

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

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. As with RHD the lower primary port goes to the caliper on the same side of the car as the master cylinder. The upper port goes to the caliper on the other side of the car, over the heater: (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 does it? Step 3 says 'Disconnect the secondary feed pipe', but pipe 3 is shown positioned and angled for the lower primary port for a caliper. Step 4 says 'Disconnect the primary feed pipes ... a Left-hand brake b Right-hand brake' but shows 4a positioned by the secondary circuit port which is for the rear brakes. So the drawing has the labelling for pipes 3 and 4a reversed. Also it is for an LHD car with one primary and the secondary going up to cross the engine bay over the heater for the right-hand caliper and the rears, the other primary going down to the left-hand caliper. An RHD car would only have one primary pipe going over the heater to the left-hand caliper, the other primary and the secondary would go down to the right-hand caliper and the rears:

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. This is quite possibly harks back to the remote plastic reservoir that France and the Benelux countries had from car number 119500 in April 67. How long for isn't known, but it would definitely have gone by the time either of the dual masters were provided as they were both translucent anyway: (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: