Preparatory work
Disconnect the battery lead. See: Battery, disconnecting .
It is important that no contaminants enter the brake system.
Before starting work, clean around the brake fluid reservoir cap and the pipe couplings.
If necessary, also clean the hose connections and the connections between the reservoir and the master cylinder.
Relieve the check valve in the power brake booster; alternatively pump the brake pedal until it has no travel.
This is so that no vacuum remains when the master cylinder is removed. Otherwise there is a risk that the O-ring will be sucked into the brake booster.
HINT: Position paper under the master cylinder to protect the paintwork.
Never, under any circumstances, open the master cylinder. Reassembling it requires special equipment and facilities.