Is upgrading the brakes reliable?

Brake King, this is a well-known product in the heavy truck circle, and many truck drivers who drive modified vehicles are not unfamiliar with it. Simply put, it is a relay valve that increases the air volume, which ultimately transmits force to the brake drum through the sub-pump air chamber. Many users who have tried it have reported good results, with very powerful brakes, making it a great enhancement for trucks that frequently drive on mountain roads or long downhill slopes while heavily loaded. However, some truck drivers believe that installing Brake King may cause damage to other components of the braking system, or even lead to accidents. So, is it really reliable to modify with Brake King?

The quality of braking performance is absolutely not to be overlooked. I once heard an experienced driver say, 'If you want to learn how to drive, you must first learn how to brake.' This is especially true for heavy-duty trucks, as the braking system is directly related to the driver's life safety. Whether it's modifying brakes for better performance or adding an ABS braking system, the intention is always to reduce the occurrence of accidents.

Forum friend 'Yonghong', whom we usually call Brother Hu, is an experienced veteran with many years of experience in brake system repair. This time, Truck Home made a long trip to Changli to visit the repair station run by Brother Hu and to consult him about his views on brake systems.● Brake Testing Structural PrinciplesIn order to test the braking effect more intuitively and provide quantifiable data, Brother Hu has created two simulation test benches for the tractor and trailer respectively. Both test benches are equipped with ABS devices. In this article, I will focus on the tractor's braking system. This tractor braking system simulation test bench has a total of four axles, which can accommodate the testing of two mainstream tractor braking systems in the market, 6×2 and 6×4. The simulated wheelbase is identical to that of a real vehicle, and it includes all necessary components such as control switches and brake pedals.

The front half of the test bench is for the steering brake of the 6×2 vehicle model. This part of the braking system consists of a main control valve, a steering brake relay valve, and two ABS solenoids. It employs a left-right air circuit control format, meaning that the left and right sides of the first and second steering axles are controlled separately, as the steering wheel of the tractor's braking belongs to lateral control. As for the layout of the ABS sensors for the steering wheels of the 6×2 vehicle models, major manufacturers vary. For example, Foton places the sensors on the first axle, while Sinotruk arranges them on the second axle.

Based on years of maintenance experience, the layout positions of sensors do vary, influenced by factors such as the weight load of the axles. Personally, Hu Ge believes that for 6×2 models, the sensor layout of the steering axle on the second axle is superior to that on the first axle.

In the rear drive axle section, we can see that it consists of the tractor's air reservoir, the trailer valve, the rear axle relay valve, and the parking relay valve. Here, we particularly mention the trailer valve, which controls how the total pump and handbrake signal operate the trailer's braking, all of which must be converted through the trailer valve device. The rear axle relay valve is used to control the braking of the drive wheels.

Through this test bench, it is clear that the principle of the tractor brake system is relatively simple, mainly controlled by a master cylinder and different relay valves. ● Blind modifications affect braking. As the mileage of vehicle transportation accumulates, the original braking system will have varying degrees of issues, primarily manifested in insufficient braking force. In such cases, many drivers choose to replace the original trailer valve with a brake king, as described earlier.

Regarding this practice, Hu believes that many drivers modify their brake systems to increase the air volume, which is due to their subjective driving habits. After increasing the air volume in the brake system, they will feel that the response time of the trailer's brakes is very short, and the braking effect is better.

But in fact, such an approach is misguided. According to his experience, the tractor must coordinate the braking of the primary vehicle and the trailer to ensure effective braking. This is because the brake master cylinder must simultaneously control the front axle relay valve, the rear axle relay valve, and the trailer valve. If the airflow to the trailer valve is increased alone, it undoubtedly disrupts the coordination of the entire system. Many drivers do not understand this, and by choosing to modify their brakes, they often cause a lack of coordination between the primary vehicle and the trailer.

Schematic diagram of the principle of the brake kingIf the brake king is replaced blindly, it will accelerate the response time of the trailer brakes, causing the trailer to brake too early. When braking while driving, lightly pressing the pedal gives a good braking effect. However, if it is pressed hard or quickly, which we commonly refer to as emergency braking, the response time of the main vehicle’s brakes will be slower than that of the trailer, leading to the impression that the tractor has no brakes.

Many drivers who modify their braking systems or add relay valves to the trailer valve are trying to speed up the braking response time of the trailer, but this disrupts the linear braking effect of the entire vehicle. In such cases, Hu Ge will restore the trailer valve to its original state to reduce the risk of wheel lock caused by improper control of the brake pedal force. Just like when riding a motorcycle, if an emergency stop situation arises, one would definitely use both front and rear brakes simultaneously, rather than just relying on the rear brake. Another common issue in braking system failures is the slow return of the handbrake. According to Hu Ge, if the handbrake on the trailer returns slowly but the foot pedal braking is normal, it is definitely related to the air supply for the handbrake of the towing vehicle. National regulations require that the air supply for the handbrake must be equipped with a one-way valve, which ensures that the air pressure for the handbrake and handbrake relay valve can function even if certain air supply lines of the towing vehicle break, preventing loss of control in emergency braking situations.

On the other hand, the slow return of the handbrake is mostly related to the strength of the spring in the one-way valve. If the spring strength is too high, it will affect the flow of air. We also tested the return time of the handbrake on-site, connecting the test bench of the tractor and the trailer, and found that the return time after releasing the handbrake is about 7 seconds, which is mainly related to the one-way valve supplying air to the main vehicle's handbrake.

二控三布置形式

● Postscript: Through this visit to Hu Ge's braking system test bench, I believe everyone has gained a clear understanding of the structure and principles of the tractor part. In order to achieve better braking effects, Hu Ge also explained whether it is necessary to modify the brake king from a theoretical perspective. However, some truck friends indicated that for heavy loads and mountainous terrain, they would rather risk damaging the brake drum than not install the brake king to ensure the vehicle can stop.

Regarding driving safety, Truck Home suggests: First, try not to overload, as the consequences of doing so cannot be predicted.

Second, regular maintenance of other components of the braking system is essential; do not overlook small details that could lead to significant losses.Additionally, current regulations do not require commercial vehicles to be equipped with an ABS system. I hope truck drivers can take responsibility for themselves and opt to install ABS to assist with braking; compared to the importance of safety, the cost of installing ABS is truly insignificant.