Solving brake maintenance problems, wishing all truck drivers a safe journey home

Experienced drivers who are on the road all year round know that the maintenance of the brake system is crucial for the safety of driving a car. The car's brake system is generally divided into two types: one is called hydraulic brakes, and the other is called air brakes. Since the braking structures and working principles of the two are different, the methods for brake maintenance are also very different.

▎Hydraulic Brake

The hydraulic brake has a simple structure and small size. It only requires a brake master cylinder, wheel cylinders, a brake fluid reservoir, and connecting pipes, without needing other auxiliary equipment. Hydraulic brakes are characterized by slightly slower response, smooth braking, and lower braking force, so they are generally used in light trucks.

Principle of hydraulic braking: When we press the brake pedal, the force is transmitted to the brake master cylinder. The master cylinder is like a syringe filled with brake fluid. When the force is applied, the piston pushes the brake fluid forward. The brake fluid flows through the brake lines to the wheel cylinders at the four wheels. The wheel cylinders then push the brake pads, clamping the brake discs to achieve braking.

For cars with hydraulic brakes, check the brake fluid level before driving. If the fluid level is found to be low, immediately inspect the brake lines for leaks. Since brake fluid absorbs moisture from the air, it becomes ineffective over time, so it is best to replace it once a year.

▎Air Brakes

Compared with the structure of hydraulic brakes, air brakes are much more complicated. In addition to the master cylinder, wheel cylinders, and brake lines, they also include an air compressor (connected to the engine via a belt), air tanks, a high-pressure controller (to regulate pressure, which can reach 8 atmospheres for vehicles), relay valves, and other components. These require a large installation space and have a complex structure. Furthermore, to ensure safety, the rear wheel brake cylinders are now all equipped with spring brakes (which increases cost and complexity). Additionally, because air brakes respond quickly, act harshly, and have high force (air pressure can reach 8 atmospheres), they are mostly used on large trucks and buses.

Pneumatic Brake Principle: When we press the brake, it is equivalent to opening the master pump valve (both are check valves, allowing air in but not returning). Compressed air passes through the check valve into the rear brake spring cylinder, pushing the brake arm, which rotates the brake cam, expanding the brake shoes (mostly now made of asbestos with copper wire) to press tightly against the brake drum (cast iron), achieving the braking effect. Nowadays, dual-circuit and cross-brake pipeline systems are used to ensure that even if there is a leak in one part of the pipeline, braking can still occur.

● Inspection and Replacement of Brake Pads and Brake Discs

For trucks, especially when loaded, due to their large mass and inertia, the force on the brake pads is greater during braking, generating more heat. Most brake failures are caused by the continuous heating of brake pads during operation; therefore, the maintenance of brake pads and brake discs is crucial.

Brake pads and brake discs are wear parts, and their wear level is related to the driver's braking habits and the driving conditions. You can judge this by observing the wear of the truck's brake pads; if they reach a critical point, they need to be replaced immediately. The main maintenance for brake pads includes high-temperature protection of the pads, lubrication and maintenance of the brake caliper pistons, and cleaning of the brake discs.

Uneven Brake Pad Wear  

Like brake pads, brake discs also need to be replaced only when they have worn to the limit. Generally, when replacing three sets of brake pads, the brake discs should also be replaced. Brake discs, after frequent use, generate high temperatures due to friction. In severe cases, they can even be burned to a brick-red color. At this point, some drivers might consider cooling them with water, but in fact, this greatly damages the brake discs.  

● Inferior Drying Tanks Pose Serious Risks, Must Avoid!  

Everyone is familiar with drying tanks, which are used to filter water vapor from compressed air in the air system, preventing corrosion of air reservoirs and various pumps and valves. Therefore, whether the drying tank functions properly directly affects braking performance. Although drying tanks are not expensive, many truck drivers still try to save money and don't care much about the quality of the tank, as long as one works. Some don’t even replace it for several years.

安装在气路上的干燥罐

冒牌“亲人”干燥罐

In addition, when selecting a drying tank, we should try to choose drying tanks that have many small air vents and a stronger structure. Many drying tanks on the market use relatively large-diameter holes for their air vents. At first glance, this design seems fine, but if thinner filter paper and smaller-diameter desiccants are used, the larger pressure in the vehicle's air circuit can easily push the internal desiccant out directly into the air circuit, causing blockages and creating safety hazards.

The lifespan of a drying tank is highly related to its usage environment. Generally speaking, when the farthest air reservoir from the air compressor can release water, it indicates that the drying tank is nearing failure and should be replaced immediately with a new one.

● How to avoid water in the air circuit during winter?

In winter, various braking issues frequently arise, and problems with the air circuit are often overlooked by many drivers. When normal-temperature air passes through the air pump, it is heated, but as it travels through the pipes to the back, it gradually cools. During this cooling process, water vapor in the air condenses into liquid due to condensation. Therefore, the presence of water in the pipes in winter can cause many problems. In this situation, the drying tank becomes even more important. If the drying tank fails, excessive moisture in the air circuit can freeze and block the lines, causing brakes to become unresponsive or even fail, leading to accidents.

From another perspective, in winter, the dry and cold conditions cause many air pipelines to become very brittle, making them prone to cracks or even breakage. Once there is an air leak, the air pressure in the system cannot reach the set value, leading to brake failure and also preventing the air dryer from regenerating.

Therefore, before driving, carefully check whether the air line connectors are aged or cracked. If any issues are found, they should be replaced in time. Additionally, it is important to keep air hoses and quick couplings on hand while driving, so that they can be replaced or repaired immediately if the air line breaks. Since air lines cover a wide range, contact with the vehicle frame or other parts is inevitable. Frequent friction at contact points can accelerate the damage to the hoses, so these areas should be checked regularly and the hoses in more scattered areas should be wrapped to prevent accelerated wear.

● The air pump, often overlooked, contains valuable knowledge

The air pump is the source of air pressure for the entire vehicle, with braking being the most important application. In routine maintenance, the air pump is also one of the areas easily neglected. If proper maintenance is not performed, the air pump can suffer abnormal wear, oil leakage, and oil consumption, which in severe cases can introduce moisture or oil into the air lines, affecting the vehicle's braking performance.

Nowadays, air compressors basically take air from the intake duct, then compress it into the air storage tank. When using low-quality air filters or allowing the compressor's intake duct to operate alone, debris can easily enter the compressor, causing abnormal wear. Abnormal wear on the compressor mainly occurs on the cylinder, piston rings, and the bearings of the compressor's rotating shaft.

Long-term intake of unclean air can lead to severe cylinder wear, increased diameter, thinning of the piston rings, and inadequate lubrication by engine oil, among other issues. More severe cases can cause oil passing through the compressor, where engine oil enters the air storage tank through compression, thereby affecting braking performance and also consuming engine oil.

Scale build-up inside the air pump

Some air pumps use engine circulating water for cooling, similar to the engine block. Some truck drivers use water instead of antifreeze in daily use, which causes scale inside the air pump, blocks the water passages, and affects the pump's heat dissipation. Therefore, in maintaining the air pump, it is recommended that drivers use high-quality air filters and antifreeze, and not let the air pump intake work independently.

During a trip, the normal operation of the braking system is extremely important. Once it fails, the driver's life is at risk. Therefore, when it comes to brake maintenance, drivers must pay close attention! With the New Year approaching, we hope every driver on the road can return home safely and reunite with their spouse and children.