This is just a heads up for anyone in Australia with a 78 or later Moke (or 77 on Mini !) who's replacing the Master Cylinder.
Many (all ?) of our local suppliers seem to only stock the GMC227 Master Cylinder, sometimes referred to as a Yellow Tag type. The originals were equivalent to a GMC167 or a Green Tag type. These two Cylinders while externally, having a similar appearance are quite different.
The way the original Cylinder was plumbed up, the lower port was for the front wheels and the upper for the rears.
These Tandem Master Cylinders while having a single Reservoir, they do have an internal partition, so that should a Hydraulic Failure occur on one circuit, the fluid doesn't drain from the healthy one out through the faulted one. Here's a GMC167 Type Reservoir cut away;-
and you can see here on this GMC227 that the portion of the Reservoir closest to the Cylinder body is full and that further away is lower;-
The GMC227 has a stepped bore inside, the lower part having a bigger diameter than the upper. This is to give a slightly lower pedal pressure for the same braking. It also means that the upper port must be plumbed to the front brakes and that's where these Cylinders come unstuck. In Australia, the Brake System for these model cars had to comply with ADR35 or later, ADR35A. In that ADR it does state;-
The Reservoir capacity for the upper port is approximately 20 ml from the full mark to where the upper connecting port between the Reservoir and the Cylinder.
I've only done here some back of the envelope numbers working from stock 8.4" Discs as these are what was factory fitted to the late 1275 Californians models and is also a very popular conversion for those that are fitted with Drum Brakes.
The Pistons in these are 2" (52 mm) in diameter and new pads have a friction material thickness of 9.8 mm. If we subtract 3 mm from the pad thickness (in line with ADR35), we have a total wear of 6.8 mm. The volume displacement for these pistons is 13.7 ml each for that wear in the Disc Pads, over 4 pistons is 54.8 ml.
While I haven't done the numbers for Drum Brakes here, they too will take more fluid as per ADR35 than the Reservoir will hold.
You can easily see here, even allowing for some errors in my numbers that the 20 ml the Reservoir holds for this circuit is a long way short of the 54 ml required.
While this may appear an obscure rule, it is stamped on to the compliance plate and I am aware first hand of an Insurance claim (not mine !) being knocked back because one of these Master Cylinders was fitted.
Retro fitting a Tandem Cylinder to a car that was originally Single Circuit, ADR35 or 35A will likely still apply in most states, even though that ADR will not have been in effect when the car was built as usually (depending on the State) this is deemed a modification that needs to comply with these ADRs.
Beware.
