Brake Servo

The brake servo, or vacuum booster, is a small canister used to increase braking pressure to take the strain off the driver's foot. If a brake servo becomes damaged or worn it should be replaced. Using the vacuum produced by your car's engine, or special vacuum pumps, the brake servo boosts the natural force sent to the master cylinder when you apply pressure to the brake pedal. This action is commonly known as power braking. A black metal canister, the brake servo is located at the back of the engine compartment on the driver's side. It sits between the master cylinder and the pedal linkage, connecting the two by means of a rod that is attached to the master cylinder's piston. A valve and diaphragm system operate the brake servo, with the vacuum on either side of the diaphragm acting as the driving force that provides the extra braking assistance. Brake servos have become commonplace with the move from the drum brake to the disc brake system (at least for the front-axle wheels), while drum brakes produce extra power by design, disc brakes require assistance with this and so use brake servos to increase braking pressure.

If a master cylinder is leaking replace it. The cylinder is usually mounted on the bulkhead separating the engine and car interior. It may be fitted with a vacuum servo unit. The master cylinder is normally connected to the brake pedal by a pushrod. On some cars, particularly those originally designed for left-hand drive, it may be positioned on the nearside of the engine compartment and linked to the pedal by a cross rod. A leaking or faulty servo unit should also be replaced. It may be faulty if the brake pedal is hard to push down, and all other brake faults have been eliminated (See Bleeding the brakes). One-circuit cylinder. A master cylinder serving a single circuit braking system, and with no servo unit. Before replacing it, check the condition of the air filter, which may be causing sluggish operation. It should be changed every three years, 36,000 miles or 60,000 km. Before you disconnect brake lines or electrical leads, such as those to the stop-lamp switch or fluid-level warning light, make a sketch of where each fit. If the car has twin brake lines, this is vital. Tag them and mark the cylinder body accordingly.Be careful to note the positions of washers, bushes and pedal return springs. Check how the pushrod is fitted to the brake pedal - there may be more than one hole in the pedal arm.

The brake booster is usually part of the same 'unit' as the brake master cylinder in the engine bay, together they transfer the pressure you put on the brake pedal to the brake units at each of the wheels. The vacuum system in the Brake Servo boosts the pressure you put on the brake pedal to enable lighter and better controlled braking motion. With good reason; brakes that do not have a Brake Servo would require rather well-developed leg muscles.

Turn the engine on while pushing down lightly on the brake pedal. If your Brake Servo is not working correctly, then nothing will happen, or the brake pedal will push back against your foot, once the engine starts. This could be a sign of a Brake Servo problem or an issue with the vacuum hose.

A vacuum servo also known as a brake servo or power brake unit uses a vacuum to multiply the drivers pedal effort and apply that effort to the master cylinder. The vacuum brake servo is attached between the master cylinder and the brake pedal and assists the braking force applied by the driver.

How do you know there is something wrong with the Brake Servo?
Car doesn't stop/brake as would usually be the case.
Braking requires significantly more force to push the brake pedal than usual.
If there is a whizzing noise coming from the engine compartment.

The brake Brake Servo is prone to deterioration, especially if there are leaks in the adjoining master cylinder. If you experience any problems with the brakes in a way noted under the last question it is advisable to have the system inspected and, if necessary, have the brake booster replaced. Servicing the brakes regularly is key to ensure a prolonged working life. Always service the brakes as and when stipulated in the guidelines set out by your car's manufacturer.

The vacuum booster is a metal canister that contains a clever valve and a diaphragm. A rod going through the centre of the canister connects to the master cylinder's piston on one side and to the pedal linkage on the other. Another key part of the power brakes is the check valve.

Vacuum or really lack of vacuum pressure is the most common cause of a hard brake pedal, and therefore the first thing to look at when a hard pedal is present. Your brake system's booster works by a series of diaphragms inside the booster and air on both sides of the diaphragm.

A soft brake pedal that goes all the way to the floor can be caused by several reasons. Low brake fluid check for leaks underneath the car. If the booster is bad, then it will require more force on the pedal to stop the car. Failing master cylinder this is usually the culprit if you're not losing brake fluid.

Some manufacturers include it in their maintenance schedules and others don't. Mercedes-Benz, for example, says brake fluid should be flushed and replaced with new fluid every two years or 20,000 miles. Volkswagen says that a brake fluid flush should be done on most of its models every two years regardless of mileage.

Sometimes, the worst part of getting your car fixed is having to bring it to the garage. We are therefore happy to offer our customers a free collection and delivery service If you prearrange a collection, we will pick your car up from your home or place of work and drive it to our premises, carry out all the necessary work (having consulted you) and deliver it back to you at the end of the day.

We are able to tow, jump start or repair your vehicle if you are experiencing problems or broken down for a small fee. If we can't sadly start your vehicle, we can contact a local recovery firm to collect your vehicle for a very competitive price.

Don't want to waste your day off?
You don't have the time to take your car in for a service or repairs?
Have you got problems with getting to and from the garage?

Here at Car Services in Reading, we believe that we offer a valuable product with our Free Collection and Delivery Service, we can collect either from your place of work or from your home address. If you are unsure about whether the address you are considering having your vehicle collected from is not within our range, then please do contact us.

Car Services in Reading operate a fleet of pool cars with a dedicated driver, so wherever we are collecting from, we need to be able to leave one of our pool vehicles either in your work car park / parking space, or if in a residential area, we would need to be able to leave our car either at your house or on the road with a permit if required. We would be grateful if you could bear this in mind when booking to use our free Collection and delivery service