What Are Truck Leaf Springs? Construction & Maintenance

Leaf springs are among the most critical components in a truck’s operating system. They carry load directly from the frame, absorb shocks, and help the vehicle stay smooth and stable while moving. Understanding the characteristics, construction, and maintenance procedures of truck leaf springs helps you select the right replacement parts whenever faults or failures occur.

What is a truck leaf spring?

Truck leaf springs are part of the suspension system. Their primary function is to absorb road shocks on rough surfaces so the vehicle runs smoother and safer. A leaf spring assembly is built from stacked spring-steel plates (leaves), arranged from shortest to longest to form a unified pack. The more leaves in the pack, the stiffer the spring and the greater its load capacity. When this component fails, symptoms can include rear- or front-end instability and uneven tire wear.

Construction of a truck leaf spring

A truck leaf spring includes the following main parts:

– Spring leaves (leaf pack): The core of the assembly, made from high-elasticity spring steel. Leaves come in different sizes and are stacked from short to long to create a defined camber.

– Spring eye bushings: Polymer or metal bushings that reduce friction and isolate vibration where the spring pivots.

– Leaf spring bolts / center bolt: Fasteners that clamp and align the leaves and secure the assembly to the frame.

– Shackles and hangers: Connect the leaf spring to the frame and axle, allowing length change during deflection.

– Shock absorbers: Dampen oscillations transmitted from the spring to the chassis.

Types of truck springs

Multi-leaf springs

The most common type, made from multiple stacked spring-steel plates. Advantages include affordability and ease of service and maintenance. The trade-off is that ride comfort is not as high as with other spring types.

Coil springs (helical)

Formed from a cylindrical spring-steel bar. They are compact, provide good ride quality, and are less prone to permanent set. However, they can be costlier and more complex to service in heavy-duty applications.

Air springs (air bellows)

Constructed as flexible bellows using compressed air. They offer the best ride comfort and can level ride height under varying loads. The trade-off is bulkier packaging and more complex service requirements.

Parabolic leaf springs

Built from leaves with a parabolic thickness profile, reducing interleaf friction for a smoother ride while maintaining load capacity. They provide high durability but are typically more expensive and require more specialized service.

How truck leaf springs work

Truck leaf springs operate based on the elastic deformation of spring steel. When a truck travels over uneven roads, impacts from the surface act on the wheels and transfer into the spring. The leaves bend, the spring compresses, stores energy, and then returns to its original shape. In doing so, the spring absorbs impact and reduces vibration transmitted to the frame and cab, helping the truck ride smoothly.

Signs your leaf springs need maintenance

Excessive vibration on rough roads

The most common sign of a spring problem. Because the spring’s job is to absorb shocks, weakened or damaged springs lose effectiveness, causing the vehicle to shake noticeably over rough roads, potholes, or under heavy loads.

Unusual noises from the spring area

Noise can occur when dry interfaces rub due to insufficient lubrication, or if leaves are cracked or broken. Investigate immediately when you hear unfamiliar sounds around the spring.

Leaves bent, cracked, or broken

A severe failure mode. If you find bent, cracked, or broken leaves, replace the spring promptly to protect occupants and cargo.

Vehicle pulls or wanders while driving

Leaf springs play a key role in vehicle stability. When they are damaged, the truck may drift off-line, especially when cornering or at higher speeds.

Uneven tire wear

If tires are wearing unevenly, the spring system may be at fault. Weak or damaged springs can distribute weight unevenly across the wheels, accelerating irregular wear.

Ride height is lower than normal

A fatigued or damaged spring can lose camber, causing the vehicle to sit lower than usual – an easy sign to spot.

Leaf spring maintenance procedure

Tools & materials

– Vehicle lift or rated jack stands

– Pliers, wrenches, and a socket set

– Hammer

– Stiff brush

– Suitable lubricant

– Clean rags

– Rubber pads or bushings (if needed)

Inspect the leaf springs

Check the following leaf spiring’s components:

– Inspect leaves for bending, cracks, or breaks.

– Ensure leaf spring bolts and center bolt are not loose or corroded.

– Check the center bolt and clips/clamps for wear or damage.

– Inspect spring eye bushings for cracking, tearing, or aging.

– Examine related suspension parts such as the stabilizer bar and shock absorbers for damage.

Clean the assembly

Use a brush to remove dirt and mud from the springs, then wipe all components clean with rags.

Lubricate

Apply the appropriate lubricant to moving interfaces and fasteners per OEM guidance. Lubricate evenly and adequately to ensure smooth operation.

Reassemble

Reinstall all components in their original positions and torque fasteners to specified values.

Thaco Parts — Vietnam’s leading, trusted OEM parts manufacturer

As a strategic partner to many global automakers, Thaco Parts (a division of THACO INDUSTRIES) manufactures and supplies OEM components (glass, leaf springs, HVAC units, wiring harnesses, condensers, interior and exterior parts) to automakers such as Kia, Mazda, Peugeot, Toyota, Hyundai, and Isuzu, and exports to markets including the United States, Australia, Russia, Canada, South Korea, Japan, and more.

THACO Parts’ products comply with IATF 16949:2016, ISO 9001:2015, and ISO 14001:2015. With a deep understanding of global OEM requirements and production processes, THACO Parts develops localization roadmaps aligned with automakers’ standards.