The positions of the axles are important for a professional truck driver to understand if he or she wants to safely and legally haul a load. Many semi trucks have sliding tandem axles that are mounted directly on the frame rails under the trailer. When the weight of the load being carried is unbalanced, some of it can be transferred to the truck by sliding the axles of the trailer. This important function can adjust the off-tracking of the trailer, effect the turning radius of the rig, and shift the balance of the weight between truck and trailer axles.
Make sure the semi truck is properly coupled to the trailer. Keeping the engine running and in neutral, set the brakes for the truck only and exit the cab.
Locate the locking lever which is usually on the driver’s side of the trailer and in front of the trailer’s wheels. Lift and pull the lever’s handle until it slips into the sideways slot on the lever guide. This will disengage the locking pins. Check to make sure all four pins are retracted properly.
Return to the cab of the truck and set the trailer brakes by either pulling out the red trailer air supply valve or pulling down the trailer brake hand valve. Release the truck’s brakes by pushing in the yellow parking brake valve. With the trailer brakes holding their wheels in place, the truck can now pull or push the trailer back and forth on the slide to make the needed adjustments.
To move the tandems back, ease the truck forward in the lowest gear until the desired position is reached. To move the tandems forward, ease the truck into reverse gear until the desired position is reached.
Reset the truck’s brakes and go back to the trailer. Release the locking lever and place it into the locked position. Return to the cab of the truck.
Release the brakes on the truck only. With the trailer brakes still set, gently tug or push against the trailer to seat the locking pins. If you listen carefully, you should hear the pins when they lock into place. Set the brakes on the truck and exit the cab.
Return to inspect all four pins to be sure they are firmly seated through the holes of the tandem axles slides. Make sure the locking lever has remained locked and is secured.