Peterbilt AirTrac Suspension Issues Explained

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

What are the most common Peterbilt AirTrac Suspension issues? 

The most common  Peterbilt AirTrac Suspension issues are:

  • Equalizer Breakage in QuadraFlex
  • Rough at the rear in Flex Air
  • Control Arm Bushing wear in Air Trac
  • Tyre Scrubbing
  • Air Bags Jacked too high or sitting too Low

Different Types of Peterbilt Truck Air Suspensions 

  • Air Trac

The Air Trac is a Leaf Spring + Air Spring combination that features a Lower Radius Rod in parallel to the spring. The radius rod provision strengthens and stabilizes the suspension vertical alignment. The Lateral Torque Rod stabilizes lateral axle movement

  • Air Leaf with Tracking Rods
  • Low and Low-Low Air Leaf Tandem (built April 2004 or later) and Flex Air
  • Low and Low-Low Air Leaf Tandem (built prior to April 2004)
  • Low Air Leaf Single

Older Model Peterbilt Suspensions:

QuadraFlex 4 Spring Tandem Axle Suspension in the 90’s Model years.

Wear Plate worn out

  • The Spring Slider Wear plate, as the name suggests, wears out after a certain length of suspension life. 
  • On wear out, the Wear plate is unable to guide the Spring laterally due to excessive clearance
  • Premature failures would be due to lack of Lubrication at the leaf spring hinges and the Equalizer Hinges
  • Older truck Equalizer brackets fail mostly due to extreme wear out, and the part reaching its end of life

Rough Ride at the rear

  • Rear suspension ride feels rough
  • Rear gets unsettled going over bumps
  • The rear instability could be due to either
    • Air Suspension Pressure loss or leakage
    • Shock Absorber issues
    • Suspension Joints
    • Axle U-Bolt Tightening
  • Check if the rear suspension ride height is satisfactory. Verify if the rear air bags can be raised or lowered. This is to see if the compressor has issues with generating pressure.
  • If the Ride Height is lower than normal, the  Air Bag internal Bump stop contacts more often, resulting in a Harsh Ride Quality
  • Check, with a pressure gauge whether the air compressor produces the required pressure
  • Also see if the load sensing valve is functioning properly
  • Inspect the shock absorbers for any oil stains near the Rod seal
  • The axle U-Bolts tend to loosen if not checked regularly. Use a digital Torque wrench to verify the residual torques.

Torque Rod Bushing Wear out in Air Trac

  • The Air Trac has three Torque Rods. Two Longitudinal, parallel to the leaf spring and One Lateral Torque Rod
  • The Control Arm/Torque Rod Bushings tend to wear out quickly as they are made of Rubber
  • Aftermarket Polyurethane material Bushings tend to give better performance in terms of durability and long-term elasticity retention.

Tyre Scrubbing

  • Uneven Tyre wear on the wheels
  • The reason this happens is due to the tires missing their alignment 
  • The best way to deal with  it is to get the alignment done at a place that does alignment for Trucks. Car and Van alignment shops might not be able to do a good job.
  • If an alignment did not solve the issue, then it might be the case that the axles are bent. 
  • In order to check axle bened, you can use a straight edge plank or a sheet-metal channel of roughly 1-2 mtr and place it over the edges of both the tyres on the sidewall.
  • Ideally, there must be no gap between the tires and the plank. If there is a gap, then it means that there is an issue with either of the axles
  • Also check the center distance between the axles on both sides. Use the in-built adjustment to align the axles back to the manufacturer recommendations.

Air Bags Jacked too High or sitting too low

  • The Air Bags of the rearmost axle are jacked too high
  • Ride height adjustment not happening properly
  • The Load Levelling Valve is mostly to blame for this occurrence
  • Either the calibration would have been disturbed on the Levelling valve might be faulty
  • The Leveling Valve Rod is attached with Rubber Donut-shaped bushings. These do wear out and result in levelling problems like suspension sitting too low or too high
  • As the Leveling rod attached to the axle moves upwards and downwards, the Leveling valve opens or closes letting air in or out of the air bags until the set ride height is achieved.

Conclusion

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

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