Shocks, Struts, and Sleeves: Suspension Parts Every Truck Driver Should Know

Your suspension system plays a crucial role in ensuring both performance and safety. Whether you’re hauling freight across the Colorado Rockies or making local deliveries in Denver’s urban sprawl, your truck’s suspension components work continuously to absorb shock, stabilize the vehicle, and protect vital systems.

Yet many drivers and fleet operators don’t fully understand the individual components within these systems or how they function. This guide aims to clarify the most essential suspension parts in diesel and commercial trucks: shocks, struts, sleeves, and more. When these components operate as intended, you can expect improved ride quality, extended tire life, enhanced braking, and safer handling.

Let’s examine what these components are, how they work, and what signs indicate they may be wearing down.

The Importance of Heavy-Duty Suspension Systems

Suspension systems in heavy-duty trucks are built to endure massive loads, rough terrain, and prolonged periods of operation on the road. They not only cushion the truck against road impacts but also ensure even weight distribution, which is essential for vehicle stability.

An improperly functioning suspension doesn't just make for an uncomfortable ride—it puts your cargo, driveline, braking system, and even the integrity of your frame at risk. Neglecting the condition of your shocks or air suspension components can lead to premature tire wear, increased stopping distance, and even mechanical failure on the road.

Shock Absorbers – Controlling the Rebound

Shock absorbers are hydraulic devices that dampen the movement of your vehicle’s suspension. When your truck encounters a bump or dip in the road, the springs compress and release energy. Shock absorbers manage this rebound, preventing your wheels from bouncing excessively.

In heavy-duty trucks, these components are crucial for maintaining traction, particularly when travelling at highway speeds or on uneven surfaces. They ensure that your tires remain in contact with the road, enhancing braking and steering response.

Common Symptoms of Shock Failure

• Visible fluid leaks around the shock body.
• Excessive bounce or nose-diving while braking.
• Uneven tire wear caused by poor damping control.
• Increased vibration and road feedback in the cab.

Shocks typically need inspection every 50,000 to 100,000 miles, though this interval may vary based on driving conditions and load weights.

Struts – Supporting and Stabilizing the Suspension

Although less common in heavy-duty vehicles than in passenger cars, struts are occasionally found in medium-duty trucks or specialty fleet vehicles. Struts combine a shock absorber and a spring into a single unit, also functioning as a structural component of the suspension system.

Worn struts can significantly affect the rest of the vehicle because they support part of its weight and help maintain alignment.

Signs of Worn Struts

• Knocking or clunking noises when driving over bumps.
• Steering drift or poor directional stability.
• Sagging suspension or visibly uneven stance.
• Longer stopping distances and sluggish handling.

Replacing a strut is more complex than just swapping out a shock absorber, so early detection is crucial to prevent collateral damage to suspension mounts and steering components.

Air Suspension Sleeves and Bags – The Adjustable Solution

If your truck features air ride suspension, it likely utilizes airbags, which are also referred to as air sleeves or bellows, instead of metal springs. These flexible, rubberized components are inflated with compressed air to support the vehicle’s load.

Air ride systems provide a smoother, more adaptable ride—ideal for freight that is sensitive to vibrations or shifting. They can also be inflated or deflated based on the load, enhancing comfort and fuel efficiency when operating empty or under lighter weights.

Key Components of Air Suspension

• Airbags – The primary load-bearing element.
• Height control valves – Adjust air pressure to maintain proper ride height.
• Air compressor and air dryer – Supply and condition the compressed air system.
• Air tanks and valves – Store and distribute air as needed.

Watch For These Red Flags

• Hissing sounds or air leaks near the bags.
• Uneven ride height, especially when parked.
• The air compressor is running constantly, indicating a pressure loss.
• Vehicle sagging or bottoming out under load.

Neglecting air suspension maintenance can lead to costly breakdowns, including compressor failure or complete suspension collapse. Moisture contamination in the air system, caused by a failing air dryer, is another common issue that results in component corrosion.

Leaf Springs – The Workhorse of Traditional Suspension

Despite advancements in air suspension technology, many fleets continue to depend on leaf spring systems for their reliability, cost-effectiveness, and ease of repair. Leaf springs consist of several curved metal strips (or "leaves") stacked atop one another. These absorb shock through flexion and evenly distribute weight across the axle.

They are often found on rear axles, particularly in Class 7 and 8 trucks, where load capacity is prioritized over ride comfort.

Common Points of Failure

• Cracked or broken leaves due to overloading or metal fatigue.
• Worn bushings or shackles, causing clunking noises or rear sway.
• Corrosion, especially in harsh weather conditions or salt-prone regions.
• Loose U-bolts, leading to axle shifting or misalignment.

Regular inspection of leaf springs is a vital component of preventive maintenance schedules, especially in regions with extreme temperature fluctuations, such as Denver.

Supporting Hardware – Small Parts, Big Consequences

Your suspension system is only as strong as its weakest link. That’s why it’s essential not to overlook the supporting components that keep everything aligned and functioning smoothly:

Shock Mounts and Bushings

These rubber or polyurethane fittings isolate vibrations and prevent metal-on-metal contact. When they wear out, the result is often noisy, jarring impacts that can loosen other components.

Leaf Spring Hangers and Shackles

These brackets connect the springs to the truck frame. If they rust or become loose, it can cause misalignment or lead to structural damage.

Height Control Valves

These valves control the amount of air supplied to the air suspension bags. If they are faulty, your truck may sag on one side or fail to maintain a level ride height, resulting in premature tire and drivetrain wear.

Preventive Maintenance Tips for Long-Term Suspension Health

Identifying suspension issues early can save thousands in repairs and help prevent catastrophic failures. Here’s what every operator and fleet manager should focus on:

• Inspect suspension components every oil change or at least every 10,000 miles.
• Check for uneven tire wear, which can indicate misaligned or worn suspension.
• Test ride height in air systems with the vehicle fully loaded and unloaded.
• Listen for unusual noises, especially when driving on rough roads or braking.
• Lubricate bushings and joints, especially in high-mileage trucks operating in cold climates.

Additionally, ensure that your loads are balanced properly. Uneven distribution can place stress on one side of the suspension more than the other, leading to accelerated component failure.

Conclusion

Understanding your truck’s suspension system isn’t just a matter of technical curiosity—it’s a business decision that impacts uptime, safety, fuel efficiency, and cargo protection. By recognising the role of each component—from shocks and struts to sleeves and leaf springs—you’re better positioned to detect issues early and make informed maintenance choices.

At Krieger’s Commercial Fleet and Automotive in Denver, CO, we specialize in suspension diagnostics, inspections, and repairs for commercial fleets of all sizes. Whether you operate traditional leaf spring systems or advanced air ride configurations, our skilled technicians can ensure your trucks remain safe, efficient, and road-ready.

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