Freightliner Airliner Suspension Issues Explained(+5 Tips)

In this brief article we are going to discuss the different Freightliner Airliner Suspension problems, what the causes are, and Troubleshooting Tips.

What are the most common Freightliner Airliner suspension issues? 

The most common Freightliner Airliner suspension issues are:

  • Air Bag Leakage
  • Rough Ride Issue
  • Lateral Torque Rod bush failure
  • “Freightshaker” Wheel hop issue

Airliner Suspension

The Freightliner Airliner is a combination of Parabolic leaf spring and Air bag suspension that works in combination to provide a soft ride. The leaf spring acts as a control arm and load bearing member for Low Frequency Vibrations.

Freightliner Airbag Lean Problem

  • A common problem with Airliners is the rear airbag misalignment
  • There is a TSB 32-040 that covers the troubleshooting for the issue. You could choose to follow this detailed procedure as well.
  • For a used truck that has done close to 100K miles, there are some typical ‘wear points’ that have been reported from experience
  • The Axle-to-spring seat is a wear item which must be removed and inspected, most preferably replaced
  • The packing Shim plates between the axle seat and Leaf Spring must also be replaced.
  • While correcting the Lean problem, Shim plates are to be either added or reduced to compensate the level measurement difference between the left and right side.

Air Bag Leakage

  • Air bag leakage, in more cases, is a sudden Blow-out event because of the very nature of the duty cycle that the trucks are put through
  • The Truck Suspension Air bags are wear items, because of the constant stress on the walls of the air bag. They have a finite life depending on the amount of rough patches that the particular truck goes through

Rough Ride Issue

  • Several of the Freightliner Airliner vehicle owners have reported a rough ride issue especially coming from the front suspension
  • The issue seems to be related to the factory leaf spring setup. The Top leaf is a Leaf-and-a-half, meaning, the top leaf only extends from the rear hanger to the axle, and the second leaf or main leaf is of full length
  • The issue is best sorted out by retrofitting a Two full length leaf spring setup in the front

Lateral Torque Rod Bush Failure

  • In the Airliner rear suspension, there are a total of 2 Lateral Torque Rods (1 for each rear axle) that locate the chassis laterally to each of the 2 drive axles via rubber bushings
  • The torque rod bushes wear out and tear over time.
  • The Lateral torque rod resists the axle’s tendency to laterally drift while tight cornering
  • Torque Rod Bush wear out, therefore leads to problems in Handling behavior of the truck  and Excessive Tire wear
  • Torque Rod wear out also contributes to the rear Air bag lean, that is typically seen on Freightliner Airliners
  • The bushes, which are typically of rubber, are of a serviceable design and can be replaced with aftermarket poly bushings which offer orders of magnitude improvement in service life.

“FreightShaker” Rear axle Wheel Hop problem while Bobtailing

  • Between 45-75 mph speeds, there is a resonance in the suspension that causes the rear axle to vibrate
  • This vibration causes cupping uneven wear of the rear Tires
  • The root cause of this is due to a Driveline ‘Torque’ vibration and is rooted in a Design Flaw in the Freightliner Driveshaft support bearing position length
  • The forward Driveshaft support bearing is located too far from the Differential. This length becomes “critical” at certain cruising speeds and resonates with engine rotation, causing the driveshaft to bend during rotation (similar to a skipping rope)
  • The solution is to modify the angle of the driveshaft during cruising in the Unladen condition (without the trailer hitched)
  • The solution to do this is to extend the length of the load sensing Lever by ⅜ inch, which causes the ride height to increase by ¾ inch. This can be done by either 
    • Cutting and the extending the lever at the middle using an adjustable threading (similar to a Tie-rod), Or,
    • Replacing with a new longer Load Sensing Lever
  • With the increase in ride height, the driveshaft angle is modified

Conclusion

In this brief article we have discussed the different  Freightliner Airliner Suspension problems, what the causes are, and Troubleshooting Tips.

References

NHTSA Technical Service Bulletin titled “AirLiner Suspension Air-Spring Bag Misalignment 32-040 Troubleshooting”  https://static.nhtsa.gov/odi/tsbs/2019/MC-10168039-0001.pdf

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