Pressure bleeding is the most efficient and foolproof means of removing air from the braking system. However, it is imperative that proper preparation and precautions are taken to ensure the integrity of the operation. First, make sure that all connections are tight and dry. Follow the routing of the individual brake pipes, paying particular attention to the unions and any place where the brake line is anchored to the frame. If any line is questionable, replace it.
Next, check the master cylinder. If the fluid is anything but clear, or if it has been in the car for a year or more, remove it from the reservoir. On earlier Rover models which are equipped with metal reservoirs, check the interior of the unit since it tends to rust from the inside out. From this point, check the master cylinder, particularly at the bellows, where the pedal actuator rod enters the cylinder. Any moisture observed on the inside of the bellows may indicate leakage of the cylinder bore seal and should be dealt with before proceeding.
On vehicles equipped with a vacuum booster, a quick way to check for fluid leaks is to remove the large vacuum line from the booster and inspect the interior of the hose for moisture accumulation. Moisture found in this line is indicative of a seal failure in the master cylinder. When the cylinder is rebuilt or replaced, the condition of the booster should be ascertained. This can be done in nearly the same fashion as checking the rear portion of the master cylinder. If fluid is present in the actuator rod bellows, the booster is a likely candidate for replacement since the large rubber diaphragm has probably been dissolved. NOTE: Be sure you use a quality brake fluid. Land Rover and Atlantic British call for Castrol LMA. DOTs, silicone or other non-recommended fluids may destroy the rubber components of the cylinders due to the higher natural rubber content of English brake seals.
The pressure bleeder is simplicity itself. A small canister, similar to a garden sprayer, is filled with brake fluid and attached to the master cylinder via a fluid proof hose and adapter cap. After building approx. 5-7 PSI in the tank, a valve is opened and the entire system is pressurized. starting at the left rear wheel, open the bleed screw until all the air has evacuated and the fluid runs clear. Then proceed to the right rear wheel and repeat the process. Next do the left front and finally the right front. At this point, the entire system should be free of air. In the case of a Model 109, it may be necessary to repeat the process a couple of times.
A very basic power bleeder will cost about $70. or less and a more intricate one could be up to $250. The simpler one is more than adequate, since less than 10 PSI is required to perform this operation.