It may happen that sometimes while driving normally on the road, suddenly, the brake pedal becomes stiff, although most of the time it returns to its previous state. This can be one of the most common brake system problems. What has happened?
The brake servo, which is located between the brake pedal and the master cylinder, is a very important component of the hydraulic braking system of many vehicles. The purpose of the brake servo is to increase the force applied to the master cylinder when the driver presses down on the brake pedal. If the pedal stiffness we mentioned above is due to a failure, it may be due to the brake servo or also to one of its associated components.
How the brake servo works and how to check and repair it
Brake servo operation
A properly functioning vehicle engine sucks in air on a regular basis. A vacuum is created on one side of the brake servo diaphragm by a vacuum tube connected to the air-sucking part of the engine, while the other side remains at normal (air) pressure. The difference in pressure increases the force exerted on the master cylinder by the brake pedal. This gives you the feeling that you can stop the car with just a light touch of the brake pedal.
Solutions to brake servo problems
A vehicle’s brake servo only operates when the engine is running. When the engine is switched off, the vacuum created in the brake servo gradually disappears, so although it will be easy to press the pedal as soon as the engine is switched off, the pedal will stiffen as you press it more often because the vacuum has disappeared. Therefore, in this case you cannot assume that the hydraulic braking system is not working properly even if the lack of vacuum in the brake servo does not allow you to stop the car by simply pressing the brake pedal.
A: If the brake pedal has stiffened after repeated depressions with the engine off, but returns to normal when the engine is started, then the brake servo is working properly. If the pedal remains stiff, the driver should check that there are no leaks in the vacuum hose that could cause insufficient engine vacuum. These leaks would affect the engine at idle, which could cause the engine to stall if the idle is unstable.
B: If the vacuum hose and the one-way valve connected to the brake servo are not causing problems and the failure is occasional, then the vacuum chamber may be defective and should be replaced.
C: If we find carbon deposits clogging the tube or blocking part of the nozzle, then the brake servo may not be getting the vacuum it needs. As a result, the pedal will become stiffer and stiffer the more you use it, but it will return to normal if you wait a long time.
D: In high altitude areas, if the brake pedal is constantly depressed, the brake servo will not be able to generate sufficient vacuum, causing the brake pedal to stiffen.
The best way to reduce the likelihood of brake system failure and ensure safe and risk-free driving is to carry out frequent technical maintenance checks as we have advised in this blog.
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