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2025
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If these situations occur when braking in winter, it's probably time for maintenance.
As winter approaches, truck drivers must take proper precautions to waterproof and prevent freezing in the brake system. Excess moisture in the brake system can pose serious risks: at a minimum, it can cause the brakes to lock, preventing the vehicle from moving or causing the wheels with engaged brakes to catch fire and damage the vehicle; at worst, freezing in the brake lines can lead to brake failure and increased safety hazards. Here are some tips to raise awareness and help prevent such situations.
▎How to Prevent Brake Line Freezing from Causing Brake Failure and Increasing Safety Risks
First, let's talk about the problems that can arise when there is too much moisture in the brake lines. The four-circuit system, brake master cylinder, trailer throttle valve, relay valve, and trailer three-axle valve, or the ABS control valve – everyone knows that the entire brake system relies on these components to function. Each of them is indispensable in their interconnected roles, and if any one of them malfunctions, it can lead to failure.
For example, if the brake valve does not return smoothly after releasing the brakes, it can cause a situation called 'dragging brakes.' This can range from mild to severe, and it may cause the wheels to lock or not, especially in cases where the brakes drag without locking the wheels.
Due to the large inertia from carrying loads, truck drivers often don’t feel it. This is the time when brake drum temperatures can spike, easily causing tire fires and property damage. The reason is that there is water inside the brake valve or antifreeze has been added to the air line, which can be very hazardous.
Here are a few key points: accumulated water can destroy the lubricant inside the brake valve, causing the control piston seals to dry out. During braking, dry friction occurs between the piston and the valve body inner wall, preventing normal sliding movement. After releasing the brakes, this affects the piston's return. In an emergency braking situation, the piston could get stuck, and if the piston doesn’t come down, the valve won’t open, leading to brake failure with potentially disastrous consequences.
If excessive water accumulates above the piston, the piston may be unable to return to its original position due to water pressure from above, preventing complete separation from the valve below. A small amount of air may continue to enter the brake chamber, causing braking. See Figure 1.
Figure 1
The reason for the brake issue is as described above. Some vehicles suffer damage due to the caused brake problems mentioned earlier. Some truck drivers might blame the repair personnel or a certain pump valve, but in reality, the culprit is the moisture in the braking system and the driver's failure to properly inspect and maintain the braking system. The picture below shows what caused the brake valve to end up in this condition.
▎ What causes damage to the brake valve?
图2
Figure 3
As truck drivers probably know, moisture in the brake lines or antifreeze in the air circuits not only damages the brake valve piston chamber, but can also damage the return spring inside the brake valve air source chamber, causing it to rust and seize or break, which will lead to air leakage in the brake valve. At the same time, it can also damage the brake slave cylinders (brake chambers). Let's first look at the main vehicle's slave cylinder, Figure 4.
Figure 4
If the O-ring in the intermediate partition is damaged, the decayed push rod can cause air leakage. After releasing the handbrake, air pressure will pass from the break chamber to the foot brake chamber. Rust on the break piston and the inner wall of the break cylinder can cause dry friction, resulting in sticking, which reduces or even eliminates the breaking function. The same situation occurs in the trailer air chamber, as shown in Figure 5.
Figure 5
The push rod between the corroded service brake chamber and the parking brake chamber can wear out the O-ring, which also leads to air leakage. Truck drivers can summarize that when there are such issues, not only does the cost of repairing the brake system increase significantly, but more importantly, safety is compromised. The hazards caused by moisture in the brake system are countless.
Imagine what would happen if there is water in the brake line that freezes in winter. Some truck drivers might initially think that the handbrake won't release and the vehicle cannot move.
Congratulations, you've got half of it right—the handbrake won't release and the vehicle can't move. But that's not the worst part. Even if the vehicle can't move, it still can't stop. The most dangerous scenario is when the air supply or control lines of the service brake valve freeze; in that case, you can’t stop even if you want to. In other words, while driving, if no air passes through the brake lines, truck drivers already understand the consequences without me having to explain.
I’ve worked on brake systems for over 20 years and have seen too many similar situations. Truck drivers must take preventive measures and control moisture at the source. Many drivers think that just changing the dryer will fix the problem, but they don’t realize that not all dryers are effective. The quality of the internal molecular sieve granules varies.
Many low-quality ones don’t actually have any drying capability—they’re just decorative. Some drivers find that their original dryers had no water in the cylinder, but after replacing it with a new dryer, there’s a lot of water released. The reason is very clear.
At this point, it’s important to note that the quality of the dryer alone doesn’t determine moisture control. The air pump, condenser control methods, pipeline setup, temperature, and back-flushing cylinder all affect the result. Upgrading through technical installation can effectively control moisture. If drivers have any of the above issues or brake problems, I’m happy to provide advice for free.
▎Editor's Note
Let's leave it at that for now. I hope this article helps truck drivers become more aware, improve their safety consciousness, and take proper precautions. Remember, safety cannot be compromised. In the next article, we will talk about measures and steps to prevent vehicle brake systems from freezing in winter. Finally, Wang from Anshun Brake wishes all truck drivers: may your journeys be safe and smooth, with Anshun always by your side.
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