To spec the proper fifth wheel, it is essential to match the needs of your tractor, your trailers and your route. This sounds more complicated than it is. This article will provide:
- A general overview of the spec’ing process and the fifth wheel options available today.
- Recommended preventive maintenance to maximize fifth wheel service operation and life.
- The do’s and don’ts associated with using your fifth wheel – specifically coupling and uncoupling the trailer and fifth wheel.
Fifth wheel manufacturers categorize their products differently, so it is highly recommended that you work with a manufacturer’s representative to make sure your fifth wheel choice is the best one for you.
STEP ONE
Spec’ing a fifth wheel begins with categorizing your hauling type. In other words, what are you going to do with this truck and trailer? As a general rule, fifth wheels can be put into three workload classifications:
- Standard duty.
- Moderate duty.
- Severe duty.
There are three primary considerations that govern which of these workload classifications would be the best fit:
- Gross combination weight.
- Road type – operating environment and type of equipment used in an application.
- Axle limitation – maximum number of towed axles.
It’s important to note that the choice of a fifth wheel shouldn’t be based on weight alone. Service conditions are important because, for example, a heavy load pulled on a paved road places less stress on a fifth wheel than a lighter load pulled in severe off-highway conditions.
The types of trailers that make up your fleet are also important. A good way to look at this consideration is to know the maximum number of towed axles.
Armed with the workload classification information, you’ll want to have a discussion with the fifth wheel manufacturer. Each manufacturer has different specifications for each duty or workload class, as well as a variety of fifth wheel models for each class.
Please note that when selecting a fifth wheel, if the application or vehicle usage places the maximum capacity on a certain fifth wheel, the selection of a fifth wheel with a higher capacity is advised. The additional capacity is recommended in order to provide better service life over a longer period of time.
STEP TWO
Once you have determined if your workload classification is standard, moderate or severe, the next step is to choose the kind of fifth wheel that matches your fleet operation. Most manufacturers offer multiple fifth wheel models for each workload classification.
Each fifth wheel is comprised of a top plate and a mount.
Top Plate Options
- Greasable – The most common fifth wheel, these typically will require grease in the top plate grease channels and locking mechanism, and a thin layer over the rest of the top plate. Check with the manufacturer for the specific greasing methods and quantities they recommend.
- Low-lube – This option makes the fifth wheel easier and less time consuming to maintain because it requires no grease on the top surface. The lock mechanism does still need to be greased and maintained.
- Electronic lock sensing – Electronic sensors built into the top plate communicate with an in-cab indicator to let the driver know when the kingpin is positioned in the lock. This provides an additional check to supplement the required driver visual inspection and tug test.
- Blocked fifth wheel – This is a non-rocking fifth wheel assembly mainly for frameless dump applications.
Mount Options
There are basically two kinds of fifth wheel mounts: stationary and air sliding. Fifth wheel mounts are available in different heights so they can be ordered based on the fleet’s particular needs.
Consider tire size, fenders, trailer type and overall trailer height when choosing a mount so that the tractor and trailer can work optimally together without exceeding the legal height.
- Stationary mount – Stationary fifth wheel mounts are ideal for applications where an entire fleet is comprised of vehicles of the same length and the same trailer kingpin setting and axle loading. They are typically lighter than sliding mount fifth wheels.
- Air slide mount - Air activated or air release is a popular option for applications that require frequent adjustment. The sliding operation is controlled by an air cylinder and is controlled by a switch in the cab.
Sliding mounts are available in a variety of slide lengths to handle trailers with different lengths and kingpin settings, and even transfer weight more evenly between tractor axles.
Extra maneuverability is another benefit of a sliding fifth wheel mount. It will accommodate trailers with short landing gear clearance and allows the driver to extend the unit for maximum comfort when weight allows.
Sliding mounts also give the driver different ride-height options, allow for decreasing the gap between tractor and trailer to improve fuel economy and even permit the favorable positioning of a load, such as allowing a slight angle to a tanker.
Be advised: A visual inspection is required by law to make sure the fifth wheel is engaged, so it is always necessary to get out of the tractor and look.
Other Options
Some manufacturers offer additional options, including some that can be used on any fifth wheel system. For example, Fontaine Fifth Wheel offers a camera assist system that allows the driver to watch a trailer couple and lock or uncouple from cab.
Always ask your fifth wheel manufacturer if there are any new options available for you to consider.
TOP OPERATING CONDITION
Fifth wheel manufacturers’ PM schedules vary and severe duty fifth wheels may require more frequent PM intervals to ensure peak performance. Always consult the manufacturer’s specific recommendations to get the most service life out of your fifth wheels.
Generally speaking, fifth wheel preventative maintenance is a five-step process.
1. Clean and degrease the fifth wheel. Starting with the fifth wheel in the closed position, use a suitable solvent to clean and degrease the fifth wheel – especially the top plate, locking mechanism and throat area.
2. Visual inspection. After cleaning, inspect for damaged or missing parts.
- Make sure the fifth wheel is securely attached to the tractor.
- Pay close attention to welds and areas around bolt holes.
- Make sure there are no cracks or missing bolts.
- Make sure nothing is hanging loose under the fifth wheel.
- Make sure the bracket pins on both sides are in place and secured.
3. Function inspection. Use the pull handle to open the lock. Insert a kingpin tool to make sure the locking mechanism is functioning properly. Make sure the locking mechanism is engaged behind the kingpin. Then, retract the pull handle.
Open and close the wheel, looking for a quick, crisp closing action. If the action is sluggish, it may be due to a buildup of old grease or a bent part causing some binding. If the wheel is hard to open, it may be due to a tight or unlubricated locking mechanism.
4. Locking mechanism adjustment. Check the adjustment procedure. Because this is different for each fifth wheel manufacturer, consult the manufacturer’s manual for specific instructions.
5. Lubrication. Begin by closing the locking mechanism. Use care when the lock closes because the handle can move in quickly. Here again, each manufacturer’s locking mechanism is different, so check your fifth wheel manufacturer’s lubrication recommendations. After greasing the locking mechanism, work it back and forth several times to distribute the grease.
Spread grease all over the surface of the top plate (not necessary for low-lube fifth wheels). If there are pockets built into the top plates, be sure they are full of grease. Leave the top plate area around the locking mechanism free of grease.
For sliding fifth wheels, lightly lubricate the pivot joints of the mechanism. Then operate the mechanism to ensure that it is working properly.
Lightly oil the other moving parts in the fifth wheel. Check the manufacturer’s recommendations for regions that experience extreme and/or prolonged freezing temperatures.
Caution: Over-lubrication is costly and causes excessive build-up on fifth wheel components. Under-lubrication could lead to steering problems.
Charles Rosato is a field service manager for Fontaine Fifth Wheel (www.fifthwheel.com), a world-wide manufacturer of fifth wheels.
