Stay Hitched

| February 03, 2005

A well-maintained fifth wheel is a driver’s link to safety.

If your fifth wheel is not working the way it is supposed to, you’ve got trouble. Proper coupling, as well as regular maintenance of the fifth wheel, can save you time, money and hassle.

Perhaps the most critical aspect of the fifth wheel begins when the driver approaches the trailer to hook up. Greg Laarman, vice president of engineering for Jost International, says this is an important operation because many drivers may not realize that it’s possible for a fifth wheel to couple in a non-positive manner (known as a “high hitch”), which is a very dangerous situation.

Coupling right
The first step in coupling to a trailer is to get the trailer at the right height. The fifth wheel’s top plate and pivot are designed to guarantee proper coupling, but they can only do their job if the trailer is at the right height. This is why trailer landing gear has the low range for raising and lowering the trailer nose even when loaded.

  1. Back the tractor up to the trailer so the fifth wheel just touches the nose of the trailer. Make sure the tractor is properly lined up – the tractor and trailer are centered with one another.

  2. Get out of the cab and observe the position of the nose of the trailer upper coupler where it contacts the top plate of the fifth wheel. The trailer must touch the top plate 4-6 inches behind the pivot point of the top plate. The top plate must remain angled down at the rear, too. And the trailer must be positioned so it will have to lift up to hitch. If the trailer is too high, pull the tractor forward and use the landing gear to lower the trailer, then back the tractor back underneath. The nose of the upper coupler needs to be high enough to ride on the ramps on the top plate. If too low, raise the trailer with the landing gear, back the tractor under the trailer and recheck the height. Be sure also that the kingpin is lined up with the gap between the two top plate ramps.
  3. Once the height is correct, back the tractor under the trailer. You must be able to feel the resistance as the trailer lifts. You’ll also hear the top plate flatten out and come to rest flat against the upper coupler. Stop the tractor at this point. Then gently feather the clutch and back just until the kingpin seats and comes to rest against the forward end of the gap between the top plate ramps.
  4. While raising the landing gear, crouch down and observe the top plate where the upper coupler rests on it. There must be no visible gap between the top plate and upper coupler.
  5. After raising the landing gear and stowing the crank, get under the trailer and look at the position of the kingpin. It must be securely trapped in the locks in the fifth wheel. Also, on a Jost fifth wheel, check the release handle to make sure it is fully retracted and in the lower notch. On Holland fifth wheels, check that the nut and washer on the front of the fifth wheel rest tightly against the top plate. Other fifth wheels have a similar procedure for checking that the mechanism is properly locked. Check your owner’s manual for details.
  6. Most drivers know the importance of leaving trailer brakes on and pulling forward with the tractor to test the fifth wheel and make sure it’s properly hitched. Make sure to do this to double check that you have coupled correctly.

Cleaning and lubrication
As with almost every working part of the rig, proper lube of the fifth wheel will help keep it operating as it was designed and help prevent premature parts failure. It will even help the handling of the rig.

Rob Nissin of Holland recommends an annual steam cleaning of the fifth wheel. It’s best to remove the top plate and turn it upside down to do this. You can get this done at a truck wash if you don’t have a steam-cleaning device, and you can often hire someone to come and do it where you work on your vehicle.

To remove the top plate, on a Jost fifth wheel, remove two hex bolts and their two tab washers; then pull the bracket pin on either side. On a Holland fifth wheel, remove the nut from the vertical retaining bolt and the bolt on either side, and then remove the pin on either side. Once steam cleaning is completed – or periodically, as needed – lube the fifth wheel. This should be done thoroughly at least every six months or 60,000 miles.

On a Jost fifth wheel:

  1. Lubricate the kingpin lock through the zerk fitting on the side of the top plate.

  2. Use a light oil to lubricate all the moving parts underneath.
  3. If the fifth wheel has a slider, spray diesel fuel on the slide path of the base plate with an oil-can.
  4. Remove old grease with a safe solvent and rags. Then lube the top of the fifth wheel with a lithium-based, EP (extreme pressure) additive. See below for some suggestions on a good way to apply.

On a Holland fifth wheel:

  1. Clean old grease from all moving parts with a spray lubricant like WD40 or CRC.

  2. Grease the bracket support fittings underneath the top plate. Also grease the release handle and springs, the jaws of the locks, the yoke tips and the pocket fittings on the right and left sides. Use low-temperature grease intended for temperatures as low as
    -30 degrees F.

  3. Use a light oil (10W or 20W) or spray silicone lubricant to lubricate the cam plate profile, washers and pivot, located underneath the top plate.
  4. Use diesel fuel to lube the slide path of the base plate.

Here as well you need to lube the top plate surface where it supports the upper coupler of the trailer. Nissin recommends NGLI No. 2 grease. He suggests you apply the grease just from the top of the throat to the top of the ramps. Then back under a trailer. This will spread the grease across the trailer contact surface on top of the plate.

Inspection and adjustment
Basic fifth wheel inspection is part of a daily walk-around. What follows here is the more thorough look-see that you should do quarterly or bi-annually.

  1. Thoroughly inspect all the mounting bolts. Use a wrench to check torque. Replace any that are missing, and torque properly.

Comments are closed. strives to maintain an open forum for reader opinions. Click here to read our comment policy.