How To Adjust Semi Trailer Brakes?

How To Adjust Semi Trailer Brakes?

With the rapid development of road transportation in various places, the characteristics of semi-trailer, such as high load capacity, economy and efficiency, have attracted the attention of the industry. Gradually semi-trailer has become the main model during long-distance logistics. Many drivers who first time come into contact with semi-trailers lack deeper understanding of the structure, design, and maintenance of semi-trailers. When driving, they often feel helpless due to the failure of the braking system, sometimes it may even cause serious accidents.

As an old saying in China, “To do a good job, an artisan needs the best tools”. If you want to make the best use of your semi-trailer, you must first adjust the semi-trailer to the best condition.


There is one of the most important systems on a semi-trailer: the braking system, or what we call the brakes. Regularly checking the status of the braking system, finding problems and adjusting them in time not only can reduce the probability of accidents, but also keep the semi-trailer in the best driving state at all times.
Timely and correct adjustment of semi trailer brakes is very important for safe driving. This article will explain in detail how to adjust semi trailer brakes.

Reminder: It is recommended to check and adjust the semi trailer brakes every 3 months or every 5000 kilometers.

How to Adjust Trailer Brakes on a Semi?

Before we start explaining How To Adjust Brakes On Semi Trailer, let’s first understand how do semi trailer brakes work. If you already have a certain understanding of semi-trailer brakes, you can click to read “How To Adjust Semi Trailer Brakes“.

How Do Semi Trailer Brakes Work?

At present, most of the semi trailers produced in China adopt a dual-pipe design, that is, the control line and the air supply line, which are connected to the tractor through the control air joint.

How to Adjust Semi Trailer Brakes?

Working Principle: When the trailer brakes working, the fresh air filtered by the air filter is first compressed and pressurized by the air compressor (air pump). The gas output by the air compressor is high-pressure gas with a certain temperature and humidity. If output directly without cooling, it would cause damage or get injured. Therefore, it is necessary to cool down and filter the water through condenser pipes and dryers. After that, the drying gas is distributed to each air storage cylinder by the four-circuit protection valve.

When the vehicle is braking, the driver depresses the brake pedal to directly operate the brake valve (brake master cylinder). Brake cylinder can supply air, the brake cylinder moves after ventilation, and rotates the shoe friction brake drum through the adjusting arm, camshaft and other mechanical structures to achieve vehicle deceleration and braking.

After understanding the working principle of the semi trailer brake, let’s take a look at how to adjust the semi trailer brakes.

How to Adjust Semi Trailer Brakes?

Braking with the air brake is the most common method on large vehicles. The air brake of the semi trailer should be maintained and adjusted regularly to keep it in the best condition at all times.

How to Adjust Semi Trailer Brakes?

Semi Trailer Brake Adjustment

If the brakes of the semi trailer are found to be abnormal during inspection, such as abnormal noise, it may be caused by the loose or worn brakes. Some adjustments can be made under the premise of ensuring safety.

  1. First, release the semi trailer brake with the semi trailer connected to the tractor. Find something suitable to plug the wheels of the semi trailer to prevent the rolling while making adjustments under the semi-trailer.
  2. After ensuring absolute safety, you can lie down on your back under the trailer. This keeps each brake in view, it is easier to make adjustment. But if you plan to adjust a semi-trailer with a lower chassis such as a low flatbed semi-trailer, a removable gooseneck trailer, etc., you can adjust it on the trailer, that is, lying prone and looking down.
  3. Locate the slack adjuster at the bottom and use a 9/16 wrench to tighten the adjustment mechanism.
  4. When tightening, you will find that the S-Cam moves, and the brake shoes will approach the brake drum.
  5. After tightening, loose it to the proper position. Usually 1/2 turn loose is proper, if you want the brakes to be tighter, you can only loose 1/4 turn. But our pros don’t recommend it, because too tight brakes can lead to some accidents.
  6. After completed adjustment , you can check whether the brake is adjusted properly. With 1/2 turn loose, the lever travels about 1 inch, which is within a 2 inch tolerance.

How to Adjust Semi Trailer Brakes?

The above is all about How To Adjust Semi Trailer Brakes. During the long-term operation of trucks and semi-trailers, regular inspections and adjustments are important. Properly adjusting the semi trailer brakes to keep the semi-trailer in the best condition at all times can not only to reduce maintenance costs, but also to reduce accidents and protect life safety. If you want to learn more about semi-trailers, please continue to pay attention to our website.