Sliding Tandems on a Semi-Trailer

Sliding Tandems on a Semi-Trailer

Learn how to slide tandems on a semi-trailer safely and efficiently with our comprehensive guide. Master 16 simple steps to ensure proper weight distribution and legal compliance.

Introduction

Knowing how to slide tandems on a semi-trailer safely is an essential skill for truck drivers. Understanding the axle positions on a tractor-trailer is crucial for safe and legal hauling. Follow this detailed guide to learn how to slide tandems correctly.

What Are Sliding Tandems?

Most tandem axles can be moved forward and backward along the length of a trailer to ensure proper weight distribution on the tractor and trailer axles. Many semi-trailers have sliding tandem axles mounted directly on the frame rails under the trailer. Properly adjusting these axles can affect the off-tracking of the trailer, the turning radius of the rig, and the overall balance of the load between the truck and trailer axles.

Basic Steps to Safely Slide Tandems Forward

1. Ensure Alignment and Clear Area: Make sure the tractor and trailer are straight and that the area in front of and behind the unit is clear for sliding the tandems. The trailer should be on a solid, level surface, as it can be difficult to slide tandems on gravel or snow-/ice-covered ground.
2. Set the Parking Brakes: Engage the parking brakes of both the tractor and trailer.
3. Check Air Pressure: Make sure the air pressure is at maximum to facilitate the process.
4. Lock the Power Divider: Lock the power divider for maximum traction.
5. Activate the Trailer Hold Switch: This is also known as the Trailer Spring Brake Override Switch. If your tractor does not have this, use the trailer brake valve instead.
6. Pull the Slider Handle: Pull the slider handle out (or up, depending on the trailer) and lock it in the retainer. If you face difficulty while pulling this handle, consider using a tool for assistance or calling for help.
7. Mark the Desired Hole: Mark the hole where you want the front locking pin to land.
8. Shift the Transmission into Reverse: When operating a manual transmission truck, ensure the range selector is down or in Low-Side.
9. Release the Tractor Parking Brake: Push the yellow button to release just the tractor parking brake.
10. Back the Trailer Up: The tandems will remain stationary while the trailer moves.
11. Set the Tractor Parking Brakes: Engage the tractor parking brakes and exit the tractor safely.
12. Check the Locking Pin Position: Verify the position of the front locking pin.
13. Lock the Slider Handle: If the pin is in the desired position, remove the slider-locking handle from its retainer and let it lock into place.
14. Rock the Trailer: Shift into drive or reverse and rock the trailer gently to ensure the locking pins are firmly seated and completely through the holes.
15. Inspect the Locking Pins: Visually inspect to confirm the pins are through the holes and the locking handle is fully in.
16. Deactivate the Locks: Unlock the power divider and deactivate the Trailer Hold Switch.

How to Distribute Weight on a Tractor-Trailer

When the weight of a load being hauled is unbalanced, a driver can transfer weight by sliding the tandems either backward or forward. Remember to always slide toward the problem:

• Too Much Weight on Drive Axles: Slide the tandems forward to place more weight on the trailer axles. This is done by reversing while the tandems are unlocked.
• Too Much Weight on Trailer Axles: Slide the tandems backward to place more weight on the drive axles. This is done by driving forward while the tandems are unlocked.

Weight Transfer Calculation

The amount of weight moved when sliding tandems depends on several factors, such as how the trailer is loaded and the distance between each hole. Generally, each tandem hole accounts for approximately 250 pounds of weight transfer:

• Move Tandems Back by One Hole: Transfers 250 pounds to the tractor axles.
• Move Tandems Forward by One Hole: Adds 250 pounds to the trailer axles.

Importance of Sliding Tandems

Truck drivers should know how to properly slide the tandems on a semi-trailer for several reasons:

• Optimal Weight Distribution: Ensures the overall weight of the tractor-trailer is distributed in the best way possible.
• Legal Compliance: Helps meet the legal requirements of the states in which they drive.
• Regulatory Adherence: Follows regulations governing the distance between the kingpin on the trailer and the trailer’s tandem axle group.

Additional Tips for Sliding Tandems

• Flat Surface: Always find a flat, level surface to adjust the tandems.
• Proper Coupling: Ensure the semi-truck is properly coupled to the trailer.
• Tool Assistance: Use tools if necessary to pull the slider handle.
• Safety First: Always set brakes and ensure the area is clear before making adjustments.

Understanding Weight Limits

It’s essential to know the legal weight limits for each axle:

• Steer Axle: Maximum 12,000 lbs.
• Drive Axle: Maximum 34,000 lbs (17,000 lbs per axle).
• Trailer Axle: Maximum 34,000 lbs (17,000 lbs per axle).
• Gross Weight: Maximum 80,000 lbs.

If the truck and trailer exceed the 80,000 lb gross limit, sliding tandems will not solve the problem. In such cases, you may need to return to the shipper to adjust the load or apply for an overweight permit for the states you plan to cross.

Using On-Board Scales and Pressure Gauges

Many trucks and trailers are equipped with pressure gauges on their air suspension. Knowing how to read these gauges can help determine if an axle is overloaded. For example, if 61 psi equals 34,000 pounds for a trailer axle, a pressure reading above this indicates an overload.

Conclusion

Sliding tandems correctly is vital for safe and legal trucking operations. It ensures optimal weight distribution, compliance with regulations, and efficient use of fuel. Always consult your company guidelines and seek assistance if needed. Proper weight distribution not only enhances safety but also helps in maintaining equipment and reducing operational costs.

FAQs

How do I know if my tandems are in the correct position?

Check the load distribution and ensure it meets legal weight limits for each axle. Use onboard scales and pressure gauges for accurate measurements.

What should I do if I can’t move the tandems?

Ensure the slider handle is fully pulled out and locked. Use tools for assistance or seek help if necessary.

Why is it important to slide tandems on a level surface?

A level surface ensures accurate adjustment and prevents the trailer from moving unpredictably.

Can sliding tandems affect my fuel efficiency?

Yes, proper weight distribution can optimize fuel usage by reducing drag and improving balance.

How often should I check the position of my tandems?

Check the tandem position every time you load a new haul or whenever you notice uneven weight distribution.

What are the consequences of not sliding tandems properly?

Improper tandem positioning can lead to unsafe driving conditions, legal penalties, and increased wear on the truck and trailer.