Power assistance

While most cars have a brake servo, some do not, so check your vehicle’s set-up. Some older vehicles (such as the Range Rover P38 and various Jaguars/fords) use an electric pump that pressurises an accumulator (shown at right), with this supply of pressurised fluid providing the braking assistance. The accumulator deteriorates over time and needs periodic replacement. The same issue afflicts the powered braking system fitted to certain pre-2000 Citroëns, which is not covered in this feature.

Some hybrids, or electric vehicles, might use either accumulators, or a traditional brake servo, with the supplying vacuum provided by both the engine and an electric vacuum pump. Other methods – used especially by Nissan – employ an electric motor that acts directly on the master cylinder to provide power assistance. Teslas, BMW’S electric 'i' range and many diesel cars use a traditional servo with a vacuum pump that is either electrical, or driven by the engine. Certain Volkswagens employ an electromechanical brake servo. Thankfully, these systems appear to be fairly reliable, but check for any vehicle-specific fluid bleeding procedures.