Hi guys and girls welcome back to TruckinNutz! I’ve missed being here more than you can imagine. First my band had our first practice in 2 years, then I got sick and lost my voice for over two weeks. Then I ended up spending a weekend in Dallas and couldnt record. But alas I am back!
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I changed the order of the series. Today we are going to talk about the fifth wheel. Because it makes sense to talk about it before we hook up to the trailer.
This may turn into a longer than usual episode but its an important part of your truck and trailer and is overlooked by nearly every driver out there. So its a very important episode.
The Fifth Wheel
The term fifth wheel comes from a similar coupling used on four-wheel horse-drawn carriages and wagons. The device allowed the front axle assembly to pivot in the horizontal plane, to facilitate turning. Basically a wheel was placed on the rear frame section of the truck, which back then only had four wheels; this wheel that was placed on the frame was the “fifth wheel”, hence the name.
Today’s fifth wheels allow the trailers to slide into the fifth wheel and lock into it, and are a very reliable unit when maintained and serviced properly. The engagement of the king pin into the fifth-wheel locking mechanism is the only means of connection between tractor and trailer; no other device or safety mechanism is used. Couplers and pintle hooks use safety chains in the event of a trailer separation while going down the road. Trailer-to-trailer connection can also be made by using fifth wheels.
Inspection and Maintence
“Like any safety-related component, the fifth wheel needs to be in good operating condition to do its job properly. “It’s important to maintain the fifth wheel because it is the sole component that connects the tractor to the trailer,” says Rob Nissen, director of field sales for SAF-Holland.
Fifth wheel manufacturers recommend performing fifth wheel maintenance every three months or 30,000 miles.
“You need to lubricate it through all four seasons,” says Charles Rosato, field service manager for Fontaine Fifth Wheel. “That also gives you four chances to inspect it each year.” If you choose not to do that, you should at least clean the locking mechanism every six months or 60,000 miles.”
“A maintenance manual from SAF-Holland sums up the importance of fifth wheel maintenance. “Failure to properly maintain your fifth wheel could result in tractor-trailer separation which, if not avoided, could result in death or serious injury.”
Nissen says, “To me it is worth an hour of your time to clean the fifth wheel, look at it, check the adjustment, and relubricate it before putting it back on the street, because one failure can be catastrophic.”
After cleaning it off. Check it out for any cracks, broken welds, damaged or missing components.
On this link from Overdrive they also cover the proper cleaning and lubrication of Jost and Holland Fifth wheels. They are very different.
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.
Coupling the right way
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.
As I said before the fifth wheel is probably the most important and overlooked thing during a pretrip. But it is needed to be done for the safe operation of your truck. Whether you stay hooked to the same trailer all the time or do daily drop and hooks. It needs to be included in a daily pretrip. Keep it greased but not too much. Clean it off every 3 months and inspect it. You cant see things wrong if its covered by grease. In the winter reduce the amount of grease but keep it greased. Remember that even a small amount of water can get in between the plates and the trailer will actually hydroplane on the fifth wheel. Clean the snow off of the fifth wheel before you hook up.