Purpose of brake servo

Answer 1

The purpose of the brake servo is to provide power assistance to the braking system when then brake pedal is pushed. The brake servo is usually a flat drum-shaped unit to the rear of the brake master cylinder. Typically, on a petrol car, a hard plastic pipe connects the servo to the inlet manifold of the engine. When the engine is running, air is sucked in through the inlet manifold; this partial vacuum is stored in the servo drum, and is used to amplify the pressure exerted by the driver on the brake pedal. A one-way valve is fitted in the system, usually in the plastic pipe, to avoid the vacuum in the servo being lost when the throttle is opened or the engine switched off. With a diesel engine, insufficient vacuum is generated in the inlet manifold to work the servo, so on diesel cars the hard plastic pipe from the servo is connected to a vacuum pump, which is typically mounted on the end of the camshaft, or sometimes on the back of the alternator. The symptoms of brake servo malfunction are usually a brake pedal that feels very stiff and has to be pushed very hard to operate the brakes. One common cause is the plastic pipe split or leaking where it joins the servo or the inlet manifold. The one-way valve can also fail, as can (less commonly I would say) the servo unit itself. On diesel cars, the vacuum pump can fail or can be tired, causing the pedal to stiffen with repeated use of the brakes. Good luck from Norn Irn!