Semi-trailer leaf springs: Structure, function and maintenance

The semi-trailer spring suspension is part of the vehicle’s suspension system, serving as a shock absorber to help maintain balance and ensure stable movement on all terrains. Understanding the structure, functions, and maintenance of the spring suspension helps optimize transport efficiency, extend vehicle durability, and support customers in choosing suitable replacement parts in case of damage.

What is a semi-trailer spring suspension?

The semi-trailer spring suspension is a vital component of the suspension system, made from multiple spring leaves or high-elasticity air bags. Its function is to absorb shocks and balance loads, ensuring smooth, stable operation and enhancing load-bearing capacity.

Functions of the semi-trailer spring suspension

The semi-trailer spring suspension enhances vehicle performance and durability during cargo transport with the following advantages:

• Shock absorption: When traveling on rough roads, the spring suspension absorbs and reduces road impacts on the chassis, ensuring smooth and safe operation.
• Load balancing: It evenly distributes loads across the chassis, enabling the semi-trailer to carry heavy loads without compromising stability.
• Stability improvement: Thanks to its flexibility, the suspension enhances stability, reducing risks of rollover or loss of control, especially on challenging terrains.

Common types of semi-trailer suspensions

Leaf spring

The most common type, designed with stacked steel leaves. Simple in design, highly durable, affordable, and easy to maintain or replace. However, it offers lower shock absorption compared to other suspension types.

Parabolic spring

Made from parabolically shaped steel leaves – thin in the center and thicker at the ends – allowing better load distribution and higher load capacity. The drawback is its higher production cost, and when damaged, full replacement is usually required.

Air suspension

This type uses inflatable airbags instead of steel leaves, providing elasticity, smoother rides, and improved stability. Its drawbacks are higher installation and maintenance costs, and the airbags are prone to leakage and damage.

Coil spring

Constructed as helical steel coils, offering durability, shock absorption, and flexibility, providing smoother rides. However, coil springs are expensive, require complex maintenance, and are unsuitable for heavy loads.

Structure of semi-trailer leaf springs

A semi-trailer leaf spring suspension typically consists of the following parts:

• Spring leaves: Flat, curved, high-elastic steel strips stacked from shortest to longest. The number of leaves varies depending on load requirements.
• Spring clamps: Secure the spring leaves at fixed points (usually ends or center) to prevent shifting during operation.
• U-bolts: U-shaped bolts that fix spring leaves to the axle or other suspension parts.
• Spring pads: Placed between leaves or between leaves and axle to reduce friction and improve ride comfort.
• Bushings: Small bearings or sleeves that reduce friction at joints between spring leaves and chassis.
• Spring pins: Connect spring leaves to the chassis or suspension components, securing the leaves while allowing flexibility on rough roads.

Signs your semi-trailer spring suspension needs inspection and maintenance

Suspensions are critical in heavy trucks and semi-trailers. Regular inspection and maintenance are essential for safety and performance. Signs include:

• Unstable movement: Excessive swaying or imbalance on uneven roads may indicate worn or weakened springs.
• Unusual noises: Noises under the chassis may suggest bent, cracked leaves or loose bolts/nuts.
• Bent, cracked, or broken leaves: Deformed leaves must be replaced immediately to avoid load failure.
• Uneven tire wear: May indicate suspension issues, including faulty springs reducing vehicle balance.

• Leaning under heavy loads: Vehicle tilting to one side may indicate damaged springs or suspension parts.
• Reduced elasticity: Loss of smoothness or increased vibrations under normal loads suggests worn-out springs.
• Dirt and rust: Heavy rust at spring joints requires cleaning or replacement to avoid breakage.
• Loose bolts/nuts: Fasteners must be checked regularly; tighten or replace if loose to avoid damage and ensure safety.

Maintenance and servicing of semi-trailer spring suspension

Inspection intervals

Maintenance depends on usage frequency, terrain, and weather. General schedule:

• Monthly: Surface inspection, welds, and spring tension.
• Every 10,000 km: Check spring deflection, joints, and lubricate connections.
• Every 6 months: Full disassembly, cleaning, detailed inspection, and replacement of faulty parts.

Essential maintenance steps

• Cleaning: Remove dirt, oil, and debris regularly to improve efficiency and extend lifespan.
• Visual inspection: Check for cracks, wear, or deformation. Ensure joints and bolts remain secure.
• Lubrication: Apply specialized lubricants to reduce friction at joints for smoother operation.
• Replacement: Replace broken or deformed springs immediately to ensure safety.
• Maintenance tracking: Record all servicing and part replacements for easier monitoring and early fault detection.

View more: Differences between Semi-trailers vs. Trailers

Thaco Spring – Vietnam’s leading spring suspension brand

As a strategic partner of major domestic and international companies, Thaco Parts (a member of THACO INDUSTRIES) proudly leads Vietnam in spring suspension manufacturing under the Thaco Spring brand. Produced on advanced automated lines and strictly quality-controlled under JIS B 2710 standards, Thaco Spring products deliver superior elasticity, load capacity, smooth performance, and stability on all terrains.

The above article provides detailed information on “Structure, functions, and maintenance of semi-trailer spring suspensions.” If you are looking for a high-quality spring suspension manufacturer, Thaco Parts is a reliable and professional choice in Vietnam. Contact us today at 0235 356 7161 for consultation and support!