Not a common item on Mokes, but many have been fitted by individuals to help with brake pedal feel and to give more confidence in the braking capabilities of their Moke. This article provide a simple couple of test yu can do to check if the diaphram is still in good working order.

Disclaimer

This is not intended to tell you who to fix a problem with your brake Booster unit and unless you are suficiently capable of working on your vrakes, all work should be done by a brake or Moke Specialist. 

 Introduction

A Vacum Brake Booster is a unit that appeared on some Minis, but never Mokes, from the factory and is norammly a rather large unit seein in your brake lines between the Master Cylinder and the rest of the brake system. The intent of the Brake booster is to use the Vacum created by the engine as it retards to magnify the pressure being applied at the brake pedal through to the calipers. Although they may not leak fluid, sometimes, normally due to age, the booster function can stop working and give a much less responsive pedal. 

Inside the large round section of the unit is a large rubber diaphram that is sealed on one side with the manifold intake. This diaphram can split or puncture alloing air to pass through cause the boost function to fail and put more air than intended into your manifold causing issues with the fuel mixture of your Moke.

How test.

What you are planning to test is whether there is air passing through a failed diaphram into the carby causing a change in the fuel mixture. If a fault is found it is assumed that the same fault, punctured diaphram, is preventing the booster from working effectively. 

 Start the Moke up and listen to the noise of the engine. Unplug the black hose from the white plug in the body of the booster. Your engine should change dramatically and possibly even stop. Put you thumb over the over the black hose and it should go back to what is was originally.

With your thumb over the hose end should be the same as plugged into the Booster, neither effect air to carby. A hole in the diaphram will let air in through the booster and your Carby would have been tuned to compensate so you will get a different engine note between the booster connected and with the thumb over the hose end.

Also you might pick the engine revs speeds up when the hose is disconnected, this is a sign the carby is running rich to compensate for the hole in the booster. If the engine almost dies then hose is disconnected then it is a sign the carby is tuned right and the new source of air is starving it of fuel and there probably isn't a hole in the booster.

If in doubt, or a fault is found, get it checked professionally. 

 The most common unit found on Mokes/Mini is a the VH44 unit and can be replaced by way of change over or new unti via a Brake dealership or brake reconditioning business.