Box, flatbed, lowboy, tanker. No matter how your Mack® truck moves a trailer load, every haul has something in common. It relies on a rugged, durable fifth wheel assembly.

The fifth wheel is the only component that connects the tractor to the trailer. If it breaks or doesn’t couple correctly, you could be facing a dangerous tractor-trailer separation.

To make sure that the locking mechanism can stand up to the rigors of the road, regular preventive maintenance (PM) is key. Fortunately, cleaning and re-lubing a fifth wheel assembly takes just one hour and doesn’t require any special tools – just a little elbow grease.

Here’s a quick step-by-step checklist to get you started:

  • Use a degreasing compound or steam cleaner to remove the dirt, debris and grease from the fifth wheel and mounting bracket.
  • Inspect the assembly for cracks, wear and damaged parts, and replace as needed.
  • Check the bracket liners. Replace any liners that are broken, show excessive wear or measure less than 0.125 inches at the top of the liner. Replace all liners every 300,000 miles (for standard duty; moderate- to severe-duty, replace every 180,000 miles).
  • Apply an even film of water-resistant lithium grease to all fifth wheel-to-trailer contact surfaces, including the yoke tips, cam profile, yoke shaft, secondary lock, release handle and kingpin. Be sure to also grease the jaws to reduce wear on both the jaws and trailer pinion.

Once the assembly is cleaned and re-lubed, it’s time to test it and perform one final inspection.

Start by making sure the fifth wheel is opening and closing properly. Then, attach a trailer and measure the slack. Anything more than 0.5 inches of fore / aft movement between the top plate and trailer will result in a truck-down situation during a roadside inspection. Be sure to also check the fasteners. If 20 percent or more are missing or non-operative, the truck will also be placed out of service.

Fifth wheel PMs can be performed at any time, but manufacturers generally recommend every three months or 30,000 miles.

Before your next fifth wheel PM check, stop by your local Mack Trucks dealership to pick up all the cleaning tools you need to get started, including multi-purpose degreaser, and fifth wheel grease and slider lube. You can also order these Mack Maintenance and Repair Chemicals – and all your fifth wheel assembly replacement parts – direct from the SELECT Part Store™ anytime. Log on today to get exclusive discounts on high-demand parts and shop supplies.


Mack Trucks

Mack Blog

Service Tips

Fill out the form below to download the whitepaper on maintaining your truck.