Have you ever wondered whether the lift axles on a truck stay lowered or are raised up when the truck is parked? Our tech support team receives this questions quite often. Thankfully there are general guidelines to follow: a non-steerable lift axle will stay lowered, and a steerable lift axle will be raised when parked.
There are other factors that will affect the position of the lift axles. We compiled a handful of common questions and answers that will help clarify any outlying concerns you may have.
Question: Will the presence of spring brakes dictate what position the lift axle will default to when parked?
Answer: Yes, lift axles without spring brakes will default to the raised position when parked. Lift axles with spring brakes (non-steerable) will default to the lowered position when parked.
Question: What happens when a truck is left in reverse? Is it the same as park?
Answer: When in reverse, steerable lift axles will raise. Non-steerable lift axles will remain in whatever state the switch indicates (raised or lowered). Reverse does not affect non-steerable lift axle positions.
Question: Are there any differences between straight trucks and tractors?
Answer: For tractors, steerable lift axles cannot be lowered in the bobtail state. This is to avoid offloading the steer axle.
Question: Are there any differences between 2.1m (W990, T880, T680) and 1.9m (W900, T800, T4s, T3s) in the way the lift axles function when a truck is parked?
Answer: 2.1m has programmed default states. They are solenoid controlled and will not deviate from the behavior identified above. 1.9m has the same behavior for steerable lift axles, but non-steerable lift axles can be either raised or lowered when parked, based on the driver-controlled switch input.
This is not an exhaustive list of Q&A, so if you have additional questions, feel free to reach out to the Sales Engineering team at 425-828-5999 or by email at KW.Tech.Supt@PACCAR.com. Stay safe out there, and keep on trucking!