Brake drum

Function

Brake drums are an essential component of drum brakes. Together with the brake shoe, a brake drum forms a friction pair, which decelerates the rotation of the wheel. The brake drum also has the job of absorbing and discharging the heat generated during braking. This is particularly important because the friction effect between brake drum and brake shoe lining lessens as temperatures rise.This can lead to what is known as fading, i.e. the waning of the braking effect at high temperatures.

Aufbau der Bremstrommel

Die Bremstrommel muss ausreichend stabil dimensioniert sein. Nur so kann sie unter allen Belastungen eine ausreichende Bremswirkung erzielen. Ihr Durchmesser darf sich unter Last und bei höheren Temperaturen nicht über ein zulässiges Maß erweitern. Außerdem gewährleisten folgende Bedingungen stabile Reibwerte und einen sicheren und zuverlässigen Bremsvorgang:

• Optimale Oberflächenrauigkeit der Reibfläche
• Gute Wärmeleitfähigkeit
• Enge Form- und Lagetoleranzen

Die Bremstrommeln sind ständig Spritzwasser, Straßenschmutz und im Winter aggressiven Substanzen wie zum Beispiel Streusalz ausgesetzt. Damit sie nicht so schnell rosten, haben mittlerweile viele namhafte Anbieter Bremstrommeln im Produktprogramm, die mit einem Korrosionsschutzlack beschichtet sind. Diese Maßnahme sichert nach dem Erneuern der Bremstrommel eine langanhaltend attraktive Optik.

Bei vielen Fahrzeugen sind die Radlager in die Bremstrommeln integriert. Werden die Bremstrommeln gewechselt, sollte aus Sicherheitsgründen auch das Radlager erneuert werden. Namhafte Ersatzteillieferanten bieten Bremstrommeln mit bereits integrierten Radlagern an. Diese Komplettsätze lassen sich in der Werkstatt schneller einsetzen, wodurch Reparaturkosten gespart werden können.

Structure of the brake drum

In order to ensure sufficient braking effect regardless of load, the brake drum must be dimensioned with adequate stability. Its diameter must not expand beyond a permissible limit under load and at high temperatures. Optimum surface roughness of the friction surface, good thermal conductivity and narrow form and positional tolerances are further guarantees of stable friction values and thus reliable and safe braking.

Brake drums are constantly exposed to spray water and road grime and, in the winter, to aggressive substances such as road salt. To stop them rusting too quickly, many well-known suppliers now feature brake drums with anti-corrosion coatings in their product portfolios. Anti-corrosion coatings ensure that brake drums will continue to look good following replacement.

Many vehicle models feature wheel bearings which are integrated into the brake drums. For safety reasons, the wheel bearing must always be replaced at the same time as the brake drum. It is for this reason that well-known manufacturers offer brake drums with ready-integrated wheel bearings. These complete kits speed up garage repair work and thus cut repair costs.

Safety

The brake drum is one of the most important safety-relevant vehicle parts. It is relatively low-wear and has a long service life. However, if the wear limit is exceeded (if the inner diameter has become larger than the permissible limit) or other damage occurs (e.g. to the wheel bearing), reliable braking is no longer assured.

In such cases, the brake drum must be replaced. Brake drums should always be replaced by axle in order to avoid high differences in braking force within one axle of the vehicle.

Should a driver notice a drop in the braking effect of the drum brake, the vehicle should be taken to a specialist garage immediately. Only trained specialists are permitted to install brake drums. The manufacturer's installation instructions must be followed.

Depreciation

Like the entire drum brake system, the brake drum does not require any maintenance at all on the part of the driver. As part of regular service and maintenance, the garage will check the drum brake for wear and effectiveness. If the brake drums or other parts of the drum brake have to be replaced, only high-quality production components should be used. They must also be installed correctly. These two considerations are vital for optimum brake performance and also also help the vehicle retain its value.