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.
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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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:
- Lubricate the kingpin lock through the zerk fitting on the side of the top plate.
- Use a light oil to lubricate all the moving parts underneath.
- If the fifth wheel has a slider, spray diesel fuel on the slide path of the base plate with an oil-can.
- 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:
- Clean old grease from all moving parts with a spray lubricant like WD40 or CRC.
- 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.
- 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.
- 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.
- Thoroughly inspect all the mounting bolts. Use a wrench to check torque. Replace any that are missing, and torque properly.
- Inspect the bracket pin retaining bolts and nuts on a Holland wheel and the hex bolts on a Jost. Check the tension of all the retaining bolts and nuts for the pins on other brands.
- Check the operation of the unit using a lock tester with the tractor in a bobtail condition. A lock tester is a tool that provides an exact substitute for a standard SAE trailer kingpin. It enables you to subject the fifth wheel to the conditions of operation while observing what is happening. It can be purchased for $100-120 at a truck parts store or distributor. The fifth wheel jaws will be open from dropping the trailer. Force the tool into the fifth wheel so the mock kingpin part slides between the ramps and into the throat. The jaws should then snap around the locking tool. Make sure the jaws close tight around the kingpin part of the tool. Pull the handle and make sure the jaws will open and stay open so you can slide the tool out.
- Check the adjustment. On a Jost, the tool should fit tightly enough that there is no fore and aft play, but loosely enough that it can be rotated. On a Holland, there should be just a limited amount of fore and aft play – just 1/16 of an inch, like a bearing clearance. Also, on the Holland, the adjustment nut and washer located on the front of the top plate slides in and out as the mechanism operates. With the fifth wheel locked, the rubber bushing should just fit snugly against the front of the plate, so you can rotate it, but with some effort. If the locks are worn loose, the bushing will be too tight.
- The Jost fifth wheel has an adjusting bolt and locknut on the right side of the top plate, slightly to the rear of the centerline. If necessary, adjust the locks by first loosening the jam nut with a standard wrench. Then, if the mechanism is too tight, turn the adjustment screw clockwise one full turn. If too loose, turn the adjustment screw counterclockwise one full turn. Then retighten the jam nut. Lock and unlock the unit several times, and then recheck the adjustment. Repeat the procedure until it’s correct.
- The Holland unit is adjusted by turning the same adjusting nut where you checked the stroke of the mechanism. You turn the nut left or counterclockwise to tighten the adjustment of the locks to compensate for wear. The nut is self-locking, so you don’t need to loosen and tighten a jam nut or locknut. Turn the locknut until you can feel the fore and after clearance. After adjusting, lock and unlock the unit and recheck the adjustment. Make sure you can still rotate the bushing. If still too tight, you can turn the nut a little bit farther so the bushing turns. If you go too far and it gets too lose, rotate it back until you can feel resistance when turning it.
Checking the kingpin
The trailer kingpin is the other half of the system that holds the tractor and trailer together while allowing them to articulate. While kingpins are only replaced, never repaired, you can use the correct gauge to ensure that the device is well within wear limits and will keep you and your trailer safe.
- First check the diameter of the neck, which is the smaller diameter near the middle of the height of the kingpin. This is nominally 2 inches. Use a factory kingpin gauge. The Jost gauge allows you to slide the gauge over the head of the kingpin through a round opening, and then move the gauge so the kingpin moves progressively into the tapered, narrower section. Because the gauge is tapered, it will stop when it reaches the measurement. You can read it on the gauge’s scale. If the pin slides all the way to the end of the slot, it must be replaced. The Holland gauge is of the go-no-go type. Slide the gauge’s larger opening over the kingpin and line it up vertically with the smaller diameter portion of the kingpin. If the gauge can be slid so that the kingpin passes through the smallest section of the gauge and into the slot, this portion is worn past the 1/8-inch tolerance. Repeat the check at four different angles, and make sure the dimension passes the test at every orientation. Replace if the kingpin is worn at any angle.
- Check the larger diameter, nominally 27/8-inch, with the wider slot in the Jost gauge, just as was done with the smaller diameter. Repeat at four different angles. Replace the kingpin if worn at any angle.
- Check the larger diameter with the larger go-no-go slot on the Holland gauge. If this section passes into the slot, the wear is excessive. Repeat at four different angles, and replace the kingpin if it’s worn at any angle.
- Now use the separate Jost kingpin height gauge, or the end of the Holland gauge, to check kingpin height. The wider portion of the gauge for maximum height should pass into the smaller diameter section of the kingpin when the gauge is slid along the lower surface of the upper coupler, indicating that the kingpin isn’t too high. The similar tab on the minimum end of the gauge should not pass into the smaller section. That would indicate too short a kingpin. A kingpin of incorrect length should be replaced because it will damage the fifth wheel and may even prevent secure coupling of tractor and trailer.
- Take a 48-inch straight edge and run it across the upper coupler plate – the flat portion surrounding the kingpin. The upper coupler plate should be totally flat in every direction. If bowed out or in so the straight edge does not touch all along its length, the plate must be replaced.
- Wiggle the kingpin as hard as you can in every direction. If it is not secure, have the fasteners torqued or repaired (with a replaceable kingpin), or upper coupler assembly replaced.
Kingpins are never repaired through welding. They must be replaced, and the work should only be done by an experienced technician in a reputable shop.
Performing these procedures will keep you safe by guaranteeing that your fifth hitches properly, is securely mounted and is securely linked to the trailer kingpin. The proper lube not only helps guarantee safety, but long life of the components and infrequent rebuilding.
Greg Laarman, vice president of engineering at Jost International; Mike Ginocchio, fifth wheel product manager; and Rob Nissen, director of field service at Holland International, provided detailed instructions and graphics on inspection and repair of their units for this article.
We asked some grease experts for their opinions on how to keep this important part of your tractor properly lubed.
What kind of grease should you use on the fifth wheel? First of all, you want a grease made for fifth wheels, says Dan Arcy, technical marketing manager for Shell Rotella T heavy-duty motor oil.
“It’s important to make sure you’re using the proper grease for fifth wheels,” Arcy says. “There are greases specifically for fifth wheels, and these products can help extend your maintenance intervals.”
Tom Boersig, research engineer, grease technology at ChevronTexaco, and Warren Eckert, commercial vehicle lubricants engineer, ExxonMobil Lubricants and Specialties, agree that the greases best for fifth wheel top plate lubrication are those with good tackiness, water and corrosion-resistance and load-carrying (also known as extreme pressure or EP) properties. Boersig recommends a grease with ISO 200 or better.
“Also, grease with up to 3 percent of a solid lubricant like molybdenum disulfide will provide a benefit of residual lubrication protection to the top plate,” Eckert says.
All three experts took a dim view of applying grease carelessly and having much of it end up on the ground. “At Shell, we recommend applying grease only to the lower half of the fifth wheel,” Arcy says. “Then, when you hook up the trailer, the grease will be forced along the entire fifth wheel.”
Standard NLGI No. 2 grease (with the additional specifications above) works in all but the coldest conditions. Eckert suggests NLGI No. 1 in extreme cold. Synthetics aren’t normally necessary, though Boersig observed that in extreme climates (-40 degrees F) you’d need synthetic grease just to get flow out of the grease gun.
Are there any classic errors truckers make in lubing the fifth wheel? Boersig mentioned “driving around bobtail and letting dirt, grit, road salt and water accumulate on the top plate,” and then hooking up prior to cleaning and regreasing. And make sure you use grease only from a clean container, even on the surface of the top plate.
Eckert mentioned overgreasing, and not only of the top plate, but on the locking mechanism. This, he reports, can cause sticking of the locking components and, during cold weather, can prevent the lock from engaging or releasing.
Arcy mentioned “greasing king pins, u-joints and other grease points on the vehicle and then taking the same grease and using it on the fifth wheel.” While there are greases available that will do all this, standard chassis grease generally used at the other locations is not good enough for the fifth wheel, especially the top plate.
For further information, please contact the following:
Exxon: (800) 443-9966
Mobil: (800) 662-4525
Shell Oil Co. U.S.