Knowledge!Most Comprehensive Maintenance Manual for Semi Trailers

During transportation, safety is always the top priority for truck drivers! If renting a trailer is to save worry, then the maintenance of the trailer is to maintain life. Check that there are no problems before driving, and then you can go on the road.

Based on the rich practical experience of market service professionals, we are here to summarize the use of semi trailer, semi trailer maintenance, and maintenance knowledge guides for the reference of the majority of drivers.


Special Reminder

Welding Prohibition: Under no circumstances should any part of the main beam be welded without the guidance of a professional technician.

Thorough Instruction Manual Review: Carefully read the instruction manual and perform regular maintenance as instructed.

Maintenance Checklist:

Trailer Tire Bolts: Frequently check for loose bolts on the trailer tires.

Suspension Inspection: Inspect the suspension every two days. Adjust tie rods and verify the tightness of bolts.

Tire Pressure: Maintain specified tire pressure while driving.

Air Pipe Examination: Regularly check for air leakage in the air pipe.

Traction Pin and Semi Trailer Axle Alignment: Periodically inspect the distance between the traction pin and the center of the semi-trailer axle at both ends, ensuring an error not exceeding 1.5mm.

U-Bolt Inspection: Check for any loosening of the steel U-bolt every 5000 kilometers.

Load Distribution: Ensure the trailer is not overloaded, unbalanced, or has concentrated weight in the middle of the frame.

Spare Tire Safety: Securely fix the spare tire and lock the safety bolts in place.

Special reminder 

After driving for one month or 5000 kilometers for the first time, the wheelbase should be tested and adjusted according to the picture on the right.

|A-B|≤3mm |C-D|≤2mm |E-F|≤2mm

1. Introduction To The Main Assembly Of Semi Trailer

Suspension system (rigidity): Transfer load and absorb vibration.

Axle and wheel hub system: A single, two and three axle assemblies with the same structure are installed under the suspension system. The tire and rim assembly are fastened to the wheel hub with tire bolts to support the weight of the entire vehicle.

Lag ndinLeg Lifting Mechanism: To ensure secure parking of the semi-trailer after detachment from the tractor, the front end of the frame is equipped with two outriggers, either linked or single-acting. This mechanism consists of a screw drive, bevel gear drive, two-speed reduction box, transmission rod, and an operating handle.

The handle functions in two modes: when pushed in, it facilitates a rapid lifting and lowering by turning, while pulling it out allows for slower lifting and lowering by turning. When the landing legs make contact with the ground, they can only be raised or lowered in the low gear mode for enhanced stability and safety.

Kingpin and guide plate/frame: The lower part of the front end of the frame has a kingpin and a kingpin connecting plate connected to the saddle of the tractor. The kingpin is mainly used to transmit the traction force of the tractor and the braking force during braking.

2. Semi Trailer Circuit

The semi trailer transmits the light signal of the main vehicle to the trailer by connecting the spiral cable plug of the tractor to the circuit socket at the front end of the trailer. Therefore, the vehicle is equipped with an international general electrical system that matches the tractor. The electrical system is generally composed of seven-core sockets, multi-core cables, junction boxes, waterproof connectors, and various lamps and other components.

Seven-core circuit connection diagram:

3. Semi Trailer Gas Circuit

There are three major parts: emergency relay valve, ABS valve, and brake chamber. Most of the faults come from these three parts.

Emergency Relay Valve: Within the vehicle braking system, the pneumatic components serve a crucial role in enabling emergency braking in scenarios such as damage to the semi-trailer’s inflation pipeline or the interruption of air intake. This system efficiently reduces braking lag time and promptly releases the brakes. It replaces multiple components in the original semi-trailer system, including the brake valve, distribution valve, acceleration valve, and quick-release valve in the dynamic system.

ABS (Anti-lock Brake System): This electronic control system actively monitors and manages the vehicle’s speed while braking. Comprised of ABS solenoid valves, ABS wiring harnesses, ABS probes, gear rings, and other integral components, it collaborates with the relay valve to execute the service brake function effectively.

Its primary function is to prevent brake lock-ups by detecting wheel-end speeds through probes. When the speed diminishes to zero, the signal is relayed back to the solenoid valve. In response, the solenoid valve adjusts air pressure, mitigating braking force to prevent lock-ups, thereby significantly enhancing driving safety.

Semi trailer brake chamber

4. Semi Trailer Brake System

The system comprises the air pipe joint, inflation pipe, operating pipe, air reservoir, brake chamber, relay valve, ABS valve, ABS sensor, and wheel brake. The inflation pipeline connects to the tractor’s air cylinder via a quick pipe joint, while the control pipeline links to the tractor’s brake valve through a quick joint. During braking, all brake chambers on the semi-trailer act simultaneously, ensuring synchronous and coordinated brake operation.

Service brake: Generally, service brake (foot brake) is used during driving, which is convenient for decelerating and stopping when moving forward.

Parking brake: The parking brake is the brake used when the car is at a standstill. It is called the parking brake, also known as the “hand brake”. Its main function is to prevent the car from sliding forward and backward.

Air-cut Brake (Emergency Brake): This safety feature is activated when the air-filled pipe experiences a severe leak or is cut off, prompting the automatic execution of emergency braking within the trailer brake system. While the control pipe remains intact, the “foot brake” function becomes non-operational.

Significance: In cases of damage to the front air pump, disconnection of the inflation tube, or significant air storage cylinder leakage, the vehicle’s “foot brake” can become ineffective or fail entirely. The air brake system serves as a crucial assurance for vehicle and personnel safety.

Normal Braking Operational State:

In the normal braking state, the air brake system operates efficiently to ensure safe and controlled braking maneuvers.

When the brake pedal is stepped on, the control pipeline ① delivers air to the emergency relay valve ⑤, and the emergency relay valve ⑤ controls the ⑥ air reservoir to supply air to the brake cylinder to generate braking force; when the brake pedal is released, the emergency relay is activated, the valve quickly releases the compressed air of each sub-cylinder and quickly releases the brake state.

Feedback braking state during inflation

The trailer parks for a long time. When the brake system has no air pressure, the parking brake system (air brake) works at this time. When the tractor is inflated into the air reservoir of the trailer ⑥ through the gas supply pipeline ②, the emergency relay valve is now in a safe braking state. In the safe state, the emergency relay valve sends the compressed air to each brake cylinder. When the air pressure of the trailer ⑥ air cylinder rises to 4.5 bar, the safe state is released. This function is referred to as feedback braking function. The brake cylinder generates braking force in the inflated state, which is a safety protection function.

Automatic braking state in case of emergency air failure

When ②the air supply pipeline is accidentally damaged during driving, the compressed air in the trailer ⑥the air tank will enter the ④brake cylinder through the ⑤emergency relay valve, and automatically perform braking measures to ensure the safety of the vehicle in emergency situations, which can be used in a short time Drove to the maintenance station, but it won’t last long. When the tractor is stopped and the trailer ② gas supply pipeline needs to be disconnected, the trailer brake cylinder can also be seen to work, which is the same principle.

5. Semi Trailer Inspection And Maintenance

Vehicles need to do basic inspection and maintenance. Doing a good job in inspection and maintenance that can avoid unnecessary safety hazards and reduce the cost of use.

Tire Inspection:

Check for cuts, scratches, bulges, and abnormal tire wear; ensure proper tire pattern and normal tire pressure.

Axle Suspension:

(1) Inspect suspension support welding seams for cracks. (2) Ensure no looseness in suspension support and tire bolts. (3) Verify absence of U-shaped axle looseness.

Rim Examination:

Check for cracks and deformations in the rims.

Brake System Evaluation:

(1) Assess brake piping system and brake drum for damage, wear, or cracks. (2) Verify normal and immediate braking function. (3) Before winter driving in northern areas, check brake air circuit and emergency relay valve. (4) Ensure proper function of the main vehicle’s drying tank desiccant.

Supporting Device:

Inspect all supporting device parts for intactness and ability to function for lifting and retracting.

Wire Harness and Piping:

Ensure no cracks, abrasions, or air leakage in the wiring harness and air pipe; ensure good condition of wiring harness connectors.

Lamps and Labels:

(1) Check lamps for integrity and clear visibility during operation. (2) Ensure clear and intact labels without covering or detachment.

Kingpin Examination:

Check for excessive wear beyond normal values in the kingpin.

Box Body and Door Inspection:

(1) Ensure secure connection between the box body and semi-trailer locking device. (2) Verify normal functionality of door lock device; check for undamaged sealing rubber strip.

Other Checks:

Ensure no fastener loosening, cracks in welds, or significant wear and aging of rubber components.

Hub Maintenance Operations:

Disassemble and inspect the hub system, clean shaft head and internal/external bearing failure grease. Replace with qualified new grease if needed. Assess bearing wear and condition of brake pads, drums, and other components. Perform maintenance and replacement based on inspection results.

Maintenance Cycles:

① BPW Axle: Maintenance frequency at 120,000-150,000 kilometers. ② VALX Axis: Maintenance frequency every 2 years or 400,000 kilometers (1 year or 200,000 kilometers after maintenance-free period). ③ BPW 400K/600K: Maintenance frequency every 2 years or 400,000 kilometers / 3 years or 600,000 kilometers. ④ Fuwa Axle: Maintenance frequency at 50,000-70,000 kilometers.

Calcium-Based Grease:

Apply calcium-based grease to parts like semi-trailer legs, adjusting arms, camshafts, balance beam pins, and leaf springs. Maintenance Cycle: Apply grease regularly every half a month to a month for regularly used vehicles, after heavy rains, and for less frequently used vehicles before use to ensure proper lubrication and reduce mechanical friction-induced component damage.

6. Container And Tire Maintenance

Introduction to the structure of container body:

Container Repair Methods:

  1. Patch Repair: Utilized for addressing holes, cracks, and similar issues.
  2. Replacement and Maintenance: Applied in cases of extensive damage or severe deformation.
  3. Putty Paint Scrape Repair: Employed for minor deformations without structural damage.
  4. Adhesive Repair: Suitable for cracks; commonly used for composite board cabinets.
  5. Liner Welding: Used for repairing cracks and welding.
  6. Sheet Metal Correction: Applied to rectify deformations and bending, such as hinges and locks.
  7. Gluing and Sealing: Addressing issues of rain or water leakage on the top or side panels.
  8. Steel Reinforcement: Targeted approach for overall deformation of composite boards and box expansion.

The influence of tire pressure

Market service experts will share trailer-related knowledge and maintenance precautions for drivers from time to time, hoping to help everyone, safety first.

7. Truck Maintenance Guides in Different Seasons

  1. Truck Interior Cleaning:

After a rainy and hot summer, bacteria tend to thrive in vehicle carpets, floor glues, and hidden corners. As autumn arrives and windows are less frequently opened, the air inside becomes stale, posing health risks due to odors and bacteria. Immediate thorough interior sterilization and cleaning are crucial for vehicle hygiene.

  1. Brake System Inspection:

Check brake fluid levels and quality deterioration. If needed, timely refill or replace. Monitor brake performance—note any weakening, deviation, brake pedal force, and wheel lock point during braking. Consider cleaning the brake system’s pipeline if necessary.

  1. Charging System Maintenance:

Inspect the generator belt post-rainy or high-temperature weather for aging or cracks. Adjust belt tightness to prevent early wear or generator bearing damage.

  1. Antifreeze Replacement:

With cooler autumn weather approaching, ensuring the vehicle’s cooling system operates optimally becomes vital.

  1. Truck Tire Care:

Unlike summer conditions where tires are not overinflated, autumn’s cooler temperatures require adjusting air pressure within specified ranges. Inspect tires for injuries, scratches, as rubber hardens in autumn and winter, decreasing friction and increasing susceptibility to air leaks and punctures.

  1. Heating Pipe and Fan Maintenance:

As temperatures drop in autumn, frost may appear. Check the defrosting vent’s wind flow and heat output under the windshield. Address any issues promptly to prevent safety hazards while driving.

  1. Air Conditioner Maintenance:

Post-summer rains and potential wading roads can lead to sand accumulation on the air conditioner’s condenser lower part. Regular maintenance and cleaning in autumn prevent silt and dust accumulation, extending the air conditioner’s lifespan. Additionally, monitor and clean the vehicle water tank to prevent sedimentation and contamination from sand or debris.

8. Vehicle Maintenance Knowledge In Winter

Handling Snow Buildup:

  1. To prevent windshield frost and icing, place unused newspapers outside the windshield before snowfall. Secure with tape to avoid frost issues the next morning.

Window Cleaning Tips:

  1. Avoid using a wet cloth to wipe windows in low winter temperatures as it can lead to freezing. Use a dry cloth for wiping, or keep one inside the vehicle.

Preventing Keyhole Freezing:

  1. In winter, frequent wiping of the vehicle door keyhole is crucial to prevent freezing due to water. Apply a small amount of lubricating oil to the keyhole. Wipe water around the door to prevent future issues.

Pre-driving Precautions:

  1. Before driving in winter, allow the vehicle to warm up by opening the door for a few minutes. This helps balance the vehicle’s interior temperature with the outdoor conditions, reducing glass frosting while driving or locking the vehicle.

Preventive Winter Vehicle Maintenance:

  1. Early winter waxing protects the vehicle’s paint as it reduces water accumulation on the body, lowering the possibility of freezing.
  2. Regularly clean tires in winter to remove debris and avoid using excessively repaired tires that become hard and brittle, compromising safety.
  3. Use professional glass cleaning fluid to avoid counterproductive effects. Adding alcohol or white wine to water can lower the fluid’s freezing point.
  4. Use winter oil to prevent engine failure due to cold temperatures.
  5. Ensure appropriate antifreeze levels; replace mixed antifreeze used for more than two years or longer than one year. Avoid mixing different types of antifreeze.
  6. Check brake fluid levels and quality, replace or refill if necessary.
  7. Monitor battery electrolyte levels, especially in severe cold, as insufficient charging can lead to battery rupture.

Mastering the above vehicle season maintenance guide, coupled with the usual vehiclee for the details of the vehicle, will surely allow you and your vehicle to have a worry-free ride in any environment.



Share this post