If the automatic adjustment arm isn’t maintained on time, brake failure can be very dangerous

First of all, it should be noted that the automatic adjusting arms used on trucks are technically mature and have been widely used in developed countries in Europe and America for many years without obvious design flaws. In terms of technological content, automatic adjusting arms have many advantages, as they can constantly adjust the optimal gap between brake shoes and the wheel hub during driving, maintaining good braking performance while avoiding the drawbacks and hassle of manual adjustments.

However, recently I discovered a very serious safety issue. There is a 6X4 tractor that's one year and five months old, and the driver reported that the brakes weren't working well. When I asked about it at the time, it seemed a bit suspicious. For a truck that's just over a year old, with the main vehicle having a full WABCO brake pump and valve, Fangsheng rear axle, a certain brand of auto-adjusting arms, and equipped with WABCO four-channel ABS, and the trailer having a 12-ton BPW axle also with WABCO four-channel ABS, how could the brakes be ineffective in such a short time? Reluctantly, I carried out a detailed inspection and found that on the main vehicle, the second and third axles had two wheel hubs with no brakes at all.
 

After further inspection, we found that the gap between the brake shoes and the wheel hub was very large. When the brake is applied, the brake shoes cannot expand properly to create enough friction with the wheel hub. This indicates that the automatic adjuster has failed and completely lost its automatic adjustment function. The more serious problem is that the automatic adjuster is designed with a manual adjustment function. When we manually adjust the brakes, after driving for a bit and using the brakes a few times, the braking effect returns to its original state. Upon rechecking, it was found that the adjuster lock could not secure properly, causing the brakes to revert to a failed state. This issue exists in other vehicles as well, and several truck drivers have even told me that within two years, most vehicles have switched completely to the old manual adjustment version. So the question arises

First, many truck drivers blindly trust automatic adjusting arms, seeing them as miracle tools. After all, the mandatory standard for automatic adjusting arms hasn’t been in place for long, and truck drivers haven’t had much exposure to this new component, lacking deeper understanding. Additionally, manufacturers don’t provide enough product explanations or usage guidance, so once we truck drivers accept them, we rarely check or pay attention to them, not knowing when they might completely fail or even imagining that they could fail entirely in just over a year. When driving on slippery roads, uneven braking can easily cause skidding accidents (even a good ABS won’t help much, as ABS isn’t foolproof in certain conditions). More seriously, in emergencies, due to the loss of braking power, the vehicle might not stop at all, leading to serious accidents.
 

Second, why does a key component with mature technology have such a short service life? Why can foreign products be widely used without issues? This inevitably raises suspicion of a product quality problem. Regarding the technical characteristics of the automatic adjusting arm, it works by setting a predetermined brake clearance value. When the brake pads exceed the limit during use, the automatic adjusting arm drives the internal one-way clutch mechanism to reduce the clearance by one notch when returning after braking, keeping the brake clearance within the normal range. After each automatic adjustment, it needs a latch to lock it in place, just like a manual adjusting arm. However, we have found that the failed adjusting arms cannot lock the adjusted clearance position. Even after manual adjustment, the clearance returns to the pre-adjusted state after just a few brake applications. I am not a professional, so I cannot provide specific technical data, only speculate based on my own experience. My previous 6×4 tractor also had the same issue. Within two years, all automatic adjusting arms were replaced with ordinary manual ones because the automatic arms seemed to have a short lifespan and unpredictable issues, and the purchase cost was several times higher than manual arms—manual ones cost tens of yuan each, whereas automatic arms exceeded 300 yuan. The damaged automatic arms we've found are mostly just over a year old. I think the design and technical features are fine; the key issue is the material used in manufacturing. High-quality components should last longer and not fail within just over a year, yet we found many failures within two years. Of course, products like these undergo extensive testing before release and should meet specific durability requirements. Since the internal mechanisms of the adjusting arm operate almost every time the brake is pressed, it relates to how many uses the component can endure (for example, tens of thousands of brakes), which puts strict demands on the material of all parts of the adjusting arm.

Thirdly, some card owners said that they've been using it for two or three years and it's been fine. That's true, there are still many card owners on the market who haven't noticed any issues with this product, which involves several factors. Firstly, the operating conditions of vehicles vary greatly. Vehicles running on flat highways have low brake frequency, so the wear and tear during use is relatively small, making the lifespan seem longer. Vehicles operating on complex roads or in hilly areas, where brakes are used more frequently, are more likely to encounter problems.

So when manufacturers consider choosing product materials, they can't just base the service life on the frequency of use under the best conditions. Of course, these kinds of products do have a warranty period (the manufacturer provides 18 months). But I think this one-and-a-half-year warranty is not ideal because the usage of vehicles varies greatly. Vehicles frequently used in mountainous or back road areas have higher braking frequency, which means problems may occur within 18 months, while vehicles used on plains or highways have lower braking frequency and may last two or three years without issues.

There are also national quality standards that must be verified through ISO/TS16949:2002. However, our country has vast territories with very different terrains, so some standards differ greatly from reality. Based on the problems found so far, it seems this automatic adjusting arm should be classified as a 'wearable part' for vehicle maintenance. But since it concerns the most critical component for safety, manufacturers must not compromise quality for profit and stay on the edge of regulations!

Sincere Advice

Finally, I suggest to manufacturers that brakes are no small matter. They affect countless lives and families’ happiness, so they must not be handled carelessly! The design life must not be based on the warranty period or standards made without practical basis. It's important to clearly state the product's service life during promotion, provide a reasonable and scientific explanation of product performance, so end users have correct knowledge and can perform scientific maintenance and inspections, ensuring the vehicle's components always function properly.

We also strongly advise truck OEMs to strictly control the quality of parts when purchasing components and not let the quality problem of a single brand ruin your brand reputation.

At the same time, we strongly suggest truck owners frequently monitor and check their brakes, because you never know when your brakes might lose a few hubs of braking power. Serious safety risks exist, and staying safe is the quickest way home.