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What Is Peterbilt Flex Air Suspension? (9 Facts Explained)

The presence of air suspension in a semi truck makes driving the vehicle comfortable and easy.

After all, the purpose of air suspension is to provide a consistent ride quality, especially on off-road and other poor road conditions.

Unfortunately, not all semi trucks have air suspension as there are many types of suspension a vehicle can use. Still, there will be a difference in your driving performance once you have this feature.

However, brands like Peterbilt are equipped with Flex air suspension.

If you want to know everything about Pete’s flex air suspension, read on to learn more.

Here’s a quick answer to what is a Peterbilt Flex Air Suspension:

The Peterbilt flex air suspension is another type of air suspension that Peterbilt introduced in the early 2000s. The primary responsibility of this feature is to provide ride quality and ease of handling to the vehicle. It is available to Peterbilt models such as 379, 387, 385, and 378.

What is the Peterbilt Flex Air Suspension?

Peterbilt flex air suspension was introduced in the early 2000s. 

The flex air suspension is a tandem suspension composed of air and leaf springs.

It features a high-quality trailing arm design, with durable aluminum beam attached to the semi-elliptic leaf spring.

The component weighs 38,000 lbs. and is known to be one of the lightweight suspensions installed in a semi truck. 

The suspension offers low chassis height and improved tank applications.

What are the Peterbilt Flex Air Suspension Parts?

Air suspension has 13 suspension parts.

Whether you’re a truck driver or operator, it’s crucial to know these parts to identify which part is having troubles, leading to a failing air suspension.

As soon as you familiarize yourself with these parts, you can easily find a remedy in case of failure or identify which component needs replacement.

Here are the complete parts of the Peterbilt Flex air suspension:

1. Drive Bracket

2. Link Spring Spacer

3. Link Spring Assembly

4. Drive Beam Assembly

5. Alignment Shim

6. Radius Road Assembly

7. Radius Road Bracket

8. U-Bolt

9. Transition Shim

10. Air Spring Assembly

11. Air Spring Support Beam

12. Shock Absorber Bracket

13. Shock Absorber

The significant features of the Flex air suspension system are link springs, drive bracket, radius road, air springs. 

Other components may not have a huge function in the air suspension, but they are vital for the entire suspension to work.

How does the Peterbilt Flex Air Suspension Work?

Peterbilt flex air suspension directly works with coil and leaf springs. These springs swap with one another for the pressurized and flexible air springs.

The air spring installed is monitored by the truck for ride height and internal air pressure. 

With the help of ride height, compressors, air pressure, air reservoir, and air dryer, a smooth and quality ride is easily achieved.

In addition, the flex air suspension is the reason behind a quiet performance of a vehicle. With this feature, you will no longer hear a clunky and loud sound usually present in heavy-duty vehicles.

Peterbilt Flex Air Suspension Ride Height

The efficiency of a vehicle can be determined by its ride height. 

As you might have known, ride height is the gap between the ground and the lowest component of a vehicle, typically the axle. It is also known as ground clearance,

The Peterbilt Flex air suspension has a ride height of 8.50 inches. It is just enough to allow the wheels to absorb road shocks. 

The highest air suspension a Peterbilt has is the Air leaf with 11.70 inches. 

However, Flex air will still work better because higher ride height is difficult to maneuver and can be dangerous to handle at times. 

With Flex air suspension, you are assured of better handling and ride quality.

How do I change the Height on my Peterbilt Flex Air?

For better vehicle performance, you can adjust the height of the Peterbilt Flex air suspension. To do this easily, make sure that the truck is parked on a flat surface. 

When you have already parked the vehicle, loosen the hose clamp and find the rod down where you can increase and decrease the height of the air suspension.

Once you have attained the proper height, tighten the clamp to lock the rod and prevent it from moving.

Height adjustment is crucial to prevent damage to the Flex air suspension.

When the truck is not loaded, the ride height is 8.50 inches. However, this height may change when you start packing the vehicle with heavy cargo.

Hence, the need to adjust the ride height. When driving a loaded truck, make sure that the ride height is at least 2.50 inches.

Does the Peterbilt Flex Air Suspension need Maintenance?

Like any other component of a semi truck, Flex air suspension likewise need maintenance. However, frequent maintenance is not required to maintain its optimal condition.

Peterbilt has recommended a particular schedule for inspection and maintenance. 

Once the semi truck reaches 5000 miles or 8000 km, inspect the runner bushings and shock absorber. If there are particular cracks or minimal damage, replace such components.

For every 10,000 miles or 16,000 km. reached, inspect all the torques in the drive beam, drive bracket, shock bracket, and air spring. 

Lastly, check the height valve operation for every 50,000 miles or 80,000 km. It’s also important to measure the pinion angle or ride height at this time. If necessary, adjust the size to maintain good function.

Meanwhile, to keep the Flex air suspension running for an extended period, always check the airline, airbag, and air springs for any leaks. 

Besides routine inspections, it’s also best to keep the service schedule to a professional mechanic. They can help you identify air suspension damage or potential problems that may arise later on.

Typical Peterbilt Flex Air Suspension Problems

Most Flex air suspension problems seem small or not a big deal; hence, they are mostly taken for granted.

However, these problems, when not resolved, may cause severe damage to the entire suspension. 

Fortunately, you can prevent these problems from happening through early detection. Some common air suspension problems include:

Air Spring Leak

A leak is common to air springs because this is the effect of the usual wear and tear. 

Fortunately, some signs will help you identify whether the air suspension is leaking. It could be a bumpy ride, the air compressor keeps running, or the ride height will drop.

These instances are indications of air spring leaks brought by deterioration. 

The air spring may also be damaged since it’s old and maybe rusty. If this is the case, it’s time to replace the air spring.

Damage from frequent moisture

The Flex air suspension has compressed air that contains moisture. With constant humidity, the components may become rusty, or it may cause air suspension failure.

Moisture is inevitable. Thus, the suspension has an air dryer to remove the moist. So when this problem occurs, the issue is the air dryer and not the compressed air.

Air Compressor burnout

Due to air leaks and overwork, the compressor may fail. The compressor is crucial to the suspension because it maintains the air springs to be inflated. 

One way to identify if the air compressor is faulty is the sudden change of the ride height. You may also hear clunking, whining, grinding sounds from the component. 

Besides the Flex air suspension, Peterbilt vehicles are also equipped with other suspension systems: Air Leaf, Air Trac, Low Air leaf, and Low Low Air leaf.

Here’s how they differ from one another:

Peterbilt Flex Air Suspension vs. Other Peterbilt Suspensions

Besides the Flex air suspension, Peterbilt vehicles are also equipped with other suspension systems: Air Leaf, Air Trac, Low Air leaf, and Low Low Air leaf.

Height Weight Commodity Hauled Intended Service
Flex Air 8.50 inches 38,000 lbs All except hay and asphalt General Freight, Car carrier, tanker, lumber, auto hauler 
Air Trac 11.70 inches 20,000 lbs to 46,000 lbs All Heavy equipment, asphalt, logger, agricultural products
Air Leaf 11 inches38,000 lbs All except hay and asphalt General Freight, heavy equipment, snow plow
Low Air Leaf (Built prior April 2004) 8.50 inches 40,000 lbs All except hay and asphalt Dump, wrecker, lube, block
Low Air Leaf (Built after April 2004) 6.50 inches (Single Drive) and 8.50 inches (Tandem Drive) 38,000 lbs All except hay and asphalt Car carrier, general freight, dump, refrigerated products
Low Low Air Leaf 8.50 inches 20, 000 lbs All except hay and asphalt General freight, city delivery, lumber, auto vehicle, emergency vehicle

As you may have observed, Peterbilt Flex air suspension is not the most powerful air suspension of the brand.

But it’s noteworthy to consider that this suspension system is one of the earliest suspensions of Peterbilt and many technology and features came later in the trucking industry.

Its biggest advantage, however, is that it’s the most lightweight. It is a good thing for truck operators who wish to gain more profit from a payload.

Which Peterbilt Models has the Flex Air System?

Peterbilt Flex Air system is an older air suspension system of the brand. Hence, they are only available on older models manufactured in the early 2000s. 

The Peterbilt trucks with Flex air suspension are 379, 387, 385, and 378. Unfortunately, these trucks have been phased out, or the brand is no longer manufacturing them nowadays. 

As such, these models with flex air suspension cannot be sourced directly from Peterbilt anymore.

You can purchase at Peterbilt trucks with Air Trac, Air Leaf, and Low Air Leaf as these are suspension systems used by newer Peterbilt models. 

However, should you want to buy a truck with Flex air suspension, you can purchase the models mentioned above from authorized sellers of used or second-hand vehicles.