Carbon brushes (motor brushes) for your car

Small cause – great effect The charge control light in the dashboard is easily overlooked. This doesn't represent a threat to the car and its safety. Nevertheless, the indicated malfunction should be fixed as soon as possible because otherwise the car can sooner or later come to a complete halt. An active control light, a headlight becoming weaker or dimmed dashboard lighting do not necessarily indicate a fully defective generator. In most cases it is only a minor fault, which can be repaired easily and at the cost of a few euros. The flow of the current The power for the lights comes from the battery which is charged by the generator. A generator consists of two copper coils: a cylindrical coil, the so-called "stator" enclosing with a few millimetres distance another coil of lacquered copper wire: the so-called "rotor". Each coil encloses an iron core. When the car is powered, the coils are electrified, creating a strong magnetic field in their core. The rotor is made to rotate by the drive belt (V-belt, flat belt, timing belt). This generates the necessary electric power. At this stage it has to be transported from the generator to the car wiring. The interface between the rotor and wire harness are the carbon brushes. Generator carbon brushes - inevitable wear parts Carbon brushes are pins made of pressed graphite. The pins are embedded in a guiding sleeve, carrying a compression spring within the sleeve. They are mounted in such a way, for them to brush against two copper rings within the generator. By doing so, the carbon brushes take electricity from the generator rotor. Inevitably, the carbon brushes wear down over time. After several ten thousands of kilometres, the graphite pins are worn down far enough for the compression spring not being able to make the contact with the copper rings anymore. This causes a generator failure. The spare part, however costs between 10 and 30 euro (£8 – 26) depending on car model and can easily be replaced. Replacing generator carbon brushes – perfect DIY job Replacing the carbon brushes in a generator is one of the easiest repairs in a car. The carbon brushes are located in a plastic casing, carrying the connection wire from the wire harness. This casing is mounted with one or two small bolts. These are removed and the complete casing with the remaining graphite pins can be taken off. The old part is simply replaced by the new unit and the generator has been repaired. Before the new part is installed, the generator can be flooded with brake cleaner, washing away the abrasions of the old carbon brushes. Prior to installing the new part it is advised to wait a few minutes until the brake cleaner is fully evaporated. Replacement of the carbon brushes separately from the casing is possible. This is an intricate job and therefore economically not worthwhile. A check-up saves additional costs Upon removal of the carbon brushes it is useful to light the casing aperture with a torch to check the copper rings. Possibly, not only the graphite pins have worn down, but the copper rings as well. This can be seen by the deep burr, left by the permanent contact of the carbon brushes. If this is the case, the new carbon brushes will wear down very quickly. If longer use of the car is to follow, replacement of the copper rings is also recommended. The generator can easily be disassembled. For a small fee, a garage can completely check and repair the generator. This generally includes a replacement of the rotor shaft bearing. Rather spend an extra pound It is recommended to replace the generator governor along with the carbon brushes. This device converts the alternating current of the generator into direct current and has several other tasks. In many models, carbon brushes and governor are already installed as a unit. If not so, the additional costs are small enough to attain a high degree of safety with little effort.