How to slide the tandem axles on a semi truck

JamieTurner Feb 23, 2008 Cars
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.

Procedure Steps

  1. 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.
  2. 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.
  3. 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.
  4. 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. 
  5. 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.
  6. 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.
  7. 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.

 Tips

  • There are evenly placed holes along the length of the tandem slide. These holes are designed to seat four locking pins that are attached to a handle called the locking lever. The lever is engaged or disengaged manually by pulling it into or out of a slot that holds it in place.
  • Off-tracking is a term describing how the rear of a trailer swings off the path of a truck’s steering wheels when making a turn. The sharper the turn, the more the rear wheels will off-track.
  • When the tandem axles are all the way back, the weight on the truck’s drive and steering axles is higher. Also, trailer off-tracking will be greater and the amount of space needed to turn increases.
  • When the tandem axles are all the way forward, the weight on the trailer’s axles is higher. This will make trailer off-tracking decrease and the amount of space needed to turn will be less.
  • The benefits of sliding the tandem axles forward when you drive in heavy downtown traffic can be offset by the possible dangers of trailer overhang.
  • Having an assistant or second driver help you slide the tandems makes the process easier. He or she can stand back at the trailer to see exactly when the correct position is reached. Without help, you’ll have to get out and check by yourself to see if you’ve moved the tandems enough.
  • A good way to keep track of important information about how to balance loads is to keep a notebook on each customer describing how you set up your load, along with other important details like the customer’s directions, phone numbers, hours of operation, and who to talk to at the shipping office.

WARNINGS!

  • Be careful when the tandem axles are all the way forward because there will be a trailer overhang.
  • The lever of the sliding tandem assembly controls four locking pins, two on each side of the trailer. Once the assembly is unlocked, be sure that all four of the pins are out completely of the holes, or you will have to repeat the entire process over.
  • The driver is responsible for the legal gross vehicle weight, the overall length of the vehicle, amount of weight per axle, and knowing all federal, state and local laws.

 

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Dave S on Oct 11, 2013
 
There is no such thing as a "semi truck". There are semi-trailers. Trailers that have no wheels in front is considered "semi" trailer.
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