Because of commercial vehicle gross-weight and axle-weight regulations, drivers will occasionally need to reposition the 5th wheel or the trailer axles for proper weight distribution. This video explains how to slide the 5th wheel and the trailer axles safely and without damaging the equipment.
After taking on a load, especially a heavy load, it’s advisable to axle-weigh the truck if possible before beginning the trip. Overweight fines are expensive and go against the fleet’s safety record.
If, after axle-weighing the truck, you discover the drive axles are 800 pounds overweight, but the steer axle is still below its legal limit, you will need to shift that weight forward to the steer axle by sliding the 5th wheel forward. Generally, weight will transfer at about 100 pounds per inch. In this example, you will have to slide the fifth wheel forward about eight inches.
With a piece of chalk, tape, or in this case, sticky notes, mark the current location of the center of the 5th wheel pivot point. Then, mark the point where the 5th wheel should be.
Where to lower the landing gear
To ease the strain on the driveline, you’ll need to lower the trailer landing gear to support the weight.
Look for solid even ground upon which to lower the landing gear, then place wheel chocks around the trailer wheels. Crank the landing gear down to about two inches from the ground, then climb into the cab and deflate the tractor air suspension.
The landing gear will settle to the ground, taking the weight off the tractor frame. As the suspension deflates, unlock the 5th wheel slider lock, then exit the cab to verify the locks have released, and to ensure the tractor is not dangling from the trailer king pin. With the weight off the 5th wheel, it should slide easily.
It will help if you mark two spots on the ground as a reference for how far the 5th wheel needs to move. In this case, we placed a pair of gloves on the ground beside the tires as guides.
Back in the cab, place the transmission in reverse, as in this case you’ll be sliding the 5th wheel forward. Release the tractor parking brakes and gently apply some throttle.
After sliding the appropriate distance, set the tractor brake and exit the cab to verify the 5th wheel is now in the correct position.
If the move was successful, re-enter the cab and re-engage the 5th wheel slide locking mechanism. Release the parking brakes and place the transmission in drive or reverse. Gently rock the truck back and forth to seat the slider locks.
Verify the slider locks have engaged, then re-inflate the tractor suspension.
As the suspension is inflating, set the tractor parking brakes. Exit the cab and crank up the landing gear and fetch the wheel chocks from the trailer. Before releasing the trailer parking brakes, do one more tug test to ensure the slider locks are fully engaged.
How to slide a trailer bogey
Next, we’ll look at sliding the trailer bogeys.
As with the 5th wheel, repositioning the trailer axles can help with weight distribution. If the trailer axles are overweight, sliding them back can transfer weight to the drive axles. Conversely, if the drive axles are overweight and the weight cannot be transferred to the steer axle, sliding the trailer bogeys forward can take some weight off the drive axles.
Unfortunately, there’s no way to take the weight off the trailer axles before sliding them, as we could with the 5th wheel by lowering the landing gear. It’s advisable to check before loading the trailer that the trailer axles are in the proper position — that is, no more than 41 feet or 12.5 meters behind the trailer king pin — and that the trailer-axle slider locks are working and the axles can slide.
Most trailers have an air-activated release for the locking mechanism, and usually, the trailer parking brake must be set for the locks to disengage. Also, the trailer air suspension may deflate when the parking brakes are set.
When the trailer is loaded, the locking pins usually will not disengage when you flip the switch. To disengage the pins, you may have to rock the tractor back and forth with the trailer brakes set.
As with the 5th wheel slider, make the current position of the locking pins with tape, chalk, or a sticky note. Also mark the position you what to slide the axles to. Release the locking pins, and deflate the trailer air suspension.
In the cab, release the tractor parking brakes, place the transmission in the direction you want to slide the trailer axles, and gently apply throttle. Be aware the slider locks may break free suddenly, so be ready to release the throttle pedal immediately.
Set the tractor parking brakes, exit the cab, and verify the trailer axles are now in the position you want them to be. Since the locking holes are usually spaced four or six inches apart, you will shift about 250 pounds per hole for four-inch spacing, and 400 pounds for six-inch spacing.
With the trailer axles successfully repositioned, re-engage the locking mechanism. The pins may not be perfectly centered on the holes, so you may need to rock the tractor back and forth to get the pins to engage. Do not venture out onto the road until the locks are engaged. If you have difficulty engaging the locks, driving slowly around and applying the trailer brakes can help. So does driving around on uneven ground.
Gather up the wheel chocks, check for lock-pin engagement, and be sure the trailer suspension is re-inflated before driving to the scale to reweigh the truck.