They are vital in active safety: if they fail, serious accidents can occur. Although this seems obvious, international surveys affirm that a large percentage of vehicles have at least one defect in the system.
Many would argue that if there is any major brake fluid leakage or the level in the pump reservoir drops too low, the warning lamp on the dashboard comes on immediately. This is only half true. In most cases, the lamp lights up, but not when there are any loose wires, poor ground contact or the lamp has simply burned out and the driver has not noticed; the warning light system has failed as well.
Of course, there are certain models (from Maserati, Aston Martin, Jaguar and other manufacturers) that, when their computerized brake management system detects a rapid drop in pressure in the hydraulic system, it immediately and automatically applies the parking brakes, to slow down or prevent the car from starting with a serious fault in a safety system. But these are isolated solutions applied in very expensive models, which can afford to incorporate brakes derived directly from aeronautics.
Brake fluid replacement
The fluid reservoir is common to the brakes and clutch, when the latter is also hydraulically controlled. The brake fluid level must be kept between the MIN and MAX marks, engraved on the wall of the plastic reservoir. If the level is below the MIN mark, the warning light on the dashboard will come on. The master cylinder must not be allowed to empty. This will cause the brakes to fail.
It is important to maintain absolute cleanliness when replenishing the brake fluid reservoir. Any dirt that gets into the system can cause a loss of braking efficiency. The symbol on the brake fluid cap in some brands, such as Ford, indicates that it may not contain kerosene. Only the fluid recommended in the vehicle manual should be used. In case of doubt, and in the case of a used vehicle for which we do not have the manual, it is best to add top brand brake fluid, which complies with the international standard DOT4. Advice on this aspect can also be obtained at a service station or at a proven lubrication center.
You can buy a small bottle of first brand and quality brake fluid. It is necessary to spend a little more, if we ask for a special small bottle of heavy-duty fluid for competition, which should also be used by vehicles traveling through mountain areas, where the brakes are very demanding. If you are offered silicone fluid, consult your trusted mechanic, because there are brake systems that are not suitable for operating with this very special and very expensive fluid. And if you happen to be a happy owner of a Rolls-Royce, keep in mind that your brake system uses a fluid that is unique in the world and is only sold by the brand’s dealers.
In ordinary cars, the brake fluid should be changed in a specialized workshop once a year, because it tends to absorb water (it is hygroscopic) and thus greatly alters its properties. This fluid is toxic and should be kept away from children. Its ingestion could lead to a fatal outcome. When changing the fluid in workshops, the system is usually purged of air so that no bubble remains in the pipes, which could cause serious braking failures. Changing the brake fluid and bleeding the system can be done by any hobbyist with sufficient experience. Otherwise, it is necessary to go to the workshop. In cars with anti-lock braking systems, things get very complicated: the best thing to do is to go to a dealer or a workshop specializing in brakes. A detail: when there is air in the system, the driver will notice that the pedal gets spongy when pressing it and increases the braking distance.
Change of tablets and ribbons
All modern cars have disc brakes on the front wheels and even discs on both axles, although most, that is, the lower-priced models, still have discs in the front and drums in the back. There are also models with solid discs, the most common, and ventilated, which are more expensive, but have greater resistance to fatigue due to the effects of heat. The high temperatures are generated by the friction material of the pads against the disc, mainly in repeated and strong braking. Drum brakes contain pads inside with tapes riveted or glued with special adhesives and, nowadays, these brakes are self-adjusting.
However, there are still tens of thousands of cars on the road that require the regulation of drum brakes (disc brakes are always self-adjusting). This regulation can also be done by the motorist who is a mechanic, without major setbacks and without spending a single weight. You can even adjust the handbrake in the traditional arrangements, just by tightening the steel cables or the system’s linkage using simple tools.
Changing the brake belts of the drums is not an easy task, and this work is done very well by workshops, which often have to have the internal surface of the drums or bells rectified, and even change the small hydraulic wheel cylinders. This is also a task for specialists: changing the pads is also a relatively simple task, but in many cases they have electrical wear sensors and you have to be careful with the connections. The pads should be checked once a month and replaced if the friction surface is worn down to almost the steel support.
If they are not replaced, they can produce irregular braking, even scratching the disc, which would be an expensive and unnecessary repair. It is often the case that the disc is so scratched that it has to be replaced. You should make sure that the new pads are the right size and material, and of first quality. Hard, “competition” type brake pads can provide better braking at high speeds, but require more pressure on the pedal and cause more abrupt braking. Although they are advisable and useful in racing cars (for example, all-metal or ceramic), should not be mounted on streetcars.
Black color and squeaks
Brake bands and pads no longer contain the highly polluting substance asbestos. It has been replaced by other friction materials, with metal content and elements such as graphite. The latter is responsible for the blackening of discs and rims in many models. Motorists also complain that their disc brakes emit annoying squeaks. Although in many cases this is due to excessive or irregular wear on the brake disc assembly, in others, this noise is natural and comes from the design of the pad itself. Sometimes it is solved by changing it for another brand, but in many cases the squeaking persists, even though the pad incorporates elements that absorb vibrations. These are the costs that have to be paid for a better protection of the environment and our health.
Asbestos is an extraordinary friction material, which provides optimal results in all aspects, but it has a dark side: medical research has shown that its micro-particles can cause malignant processes in humans and animals, so its use is prohibited in many countries, including ours. According to specialists in brakes, asbestos is allowed for the brakes of cars in a number of nations in Central America and other latitudes. These are the contradictions of the globalized world.
The brake servo
A servo mechanism can be attached to the system to reduce the effort the driver has to apply to the brake pedal. It consists of a servo cylinder, which contains a piston or diaphragm. When air is drawn from one end of the cylinder and atmospheric pressure is admitted at the other end, the pressure difference between the two sides of the piston (or diaphragm) can be used to supplement the force applied to the brake. All the assistance elements work with energy supplied by the engine. The most common brake servo takes advantage of the partial vacuum in the intake manifold; other types (for diesel) have an independent vacuum pump. If the servo stops working for any reason, the driver does not lose the braking action, although he will have to apply more pressure on the pedal and not panic. You can drive safely to the workshop.
Checking the brake lines
Rigid and flexible brake system lines are of fundamental importance for the proper functioning of the system. The rigid pipes that lead the fluid to the wheel cylinders or to the electro-hydraulic assembly of the ABS systems, are made of stainless steel or copper coated steel, with maximum resistance to the corrosive effects. They are also protected by special coatings. The flexible tubes, which connect the wheel cylinders to the main installation, are made of special elastomers (synthetic rubber). It should always be checked that there are no leaks or signs of cracks in these elements, because they could burst.
Original parts should always be installed when the replacement of hoses is necessary. A complete brake repair, which includes changing the pads and tapes, a possible rectification or replacement of the discs and drums, reconditioning of the brake pump and wheel cylinders, and perhaps a check of the brake servo, can amount to several hundredweights.
Hi, I’m Liam. I’m the initiator and writer of this blog. Cars were and will be my first love, and my favorite hobby, that’s why I decided to start this blog and write about my discoveries and techniques to improve my cars or repair them.