When it comes to fifth wheels, it is essential that all of the maintenance guidelines and procedures are in place and being followed properly. In addition, it is a good practice to conduct annual audits on proper fifth wheel maintenance and ensure that the most current training available is being conducted.
SAF-Holland recommends that every three months or every 30,000 miles, whichever comes first, routine fifth wheel maintenance and lubrication be performed.
Especially during the winter months, when vehicles are exposed to sand, road salts and other debris, it is important to conduct an inspection to be sure that these materials are not prohibiting proper operation of the fifth wheel locking mechanism. At that time, rather than just the typical lubricating of the locking mechanism, have technicians thoroughly clean it as well – something that is typically required every six months or 60,000 miles when a general fifth wheel inspection is performed.
The Right One
Proper fifth wheel choice is critical to a fleet’s uptime. It is common for operations within the fleet to change from time to time due to business requirements, and this may impact the choice of a fifth wheel to meet the application needs.
When specifying a fifth wheel, take into consideration the type of vehicle the fifth wheel will be mounted on and the type of trailer the tractor will be pulling. Also, it’s important that the fifth wheel properly match the vehicle’s duty type: standard, moderate or heavy/severe.
These same considerations, along with capacity and weight requirements, come into play when selecting a top plate for a fifth wheel. Various operating conditions, applications and loads may require a fifth wheel with greater capacities than standard fifth wheels.
Research the available top plate options to find benefits specific to applications. Those options include: right-hand release, air release, oscillating, compensating, no-tilt, manual secondary lock, low lube, no lube and more.
Capacity and Weight
Capacity also is the most critical step in selecting a fifth wheel to avert maintenance problems and, more importantly, prevent unsafe operating conditions. Specify a higher capacity rating than your normal needs require, taking into consideration the towed vehicle weight, maximum drawbar load expected, vertical load to be carried, and again, type of operation.
Be aware that top plate considerations may add weight to the fifth wheel. Standard and moderate applications may be ideal applications for lighter weight top plate options, while more demanding, heavy and severe duty applications often require a more durable top plate, typically adding weight.
Fifth wheel choice also should be a balance between operational cost, strength and durability. Extra weight may result in additional expenses, such as initial cost, reduced cargo carrying capacity and added fuel cost. But in other instances, such as with a lightweight aluminum top plate, the higher initial costs may be offset by increased payload capability.
Mounting Systems
Once you’ve selected the top plate, you can move on to the mounting system. Is a standard mounting system sufficient, or does your application require a specialized mounting system such as a no-tilt or compensator? Once determined, decide whether the application requires a stationary or sliding mount system.
Stationary mounts are best suited for applications where the axle loading, kingpin setting and vehicle combination length all remain constant throughout the fleet. These mounts are generally lighter, but do not offer the application flexibility of sliding fifth wheels.
Based on the suspension and tractor frame, one of three tractor frame attachment methods may be specified: angle-on-frame bracket mount (low cost and less torsional rigidity); foot mount (higher cost and high torsional rigidity); or outboard angle integrated plate mount (universal-hole pattern for medium torsional rigidity and bolt-on mounting).
Sliding mounts are best suited for applications where the axle loading, kingpin setting and vehicle combination length do not remain constant throughout the fleet. They are capable of transferring weight between tractor axles, accommodating trailers with different kingpin settings and varying vehicle combination lengths.
Sliding mounts, which may provide better resale, improve maneuverability in tight locations. By locating the fifth wheel closer to the centerline of the bogie or rear axle, ride comfort is increased.
Based on the suspension and tractor frame, one of two tractor frame attachment methods may be specified: over-the-frame inboard angle mount or outboard angle mount.
Height
The final step in specifying a stationary mount is to determine the height required, whereas the final step in specifying a sliding mount is to determine not only the height but the travel length required as well.
Correct fifth wheel height specification is critical because the overall tractor trailer combination height cannot exceed 13’ 6”. Fifth wheels are designed to operate with the top plate level, so every attempt should be made to match the fifth wheel height with the trailer upper coupler (bolster plate) height.
The maximum allowable fifth wheel height is determined by subtracting the trailer height and tractor frame height from the maximum height of 13’ 6”.
A standard fleet specification where all tractors have the same mounted fifth wheel height – from the ground to the top of the fifth wheel – aids in proper coupling by reducing the need to adjust trailer landing gear before coupling. Proper slide length specification is very important for the slide mount fifth wheel.
Finally, always balance the initial cost of the fifth wheel against the application required, maintenance costs, wear life and availability of parts and service.
Rob Nissen is director field service for SAF-Holland (www.safholland.us). The company specializes in trailer axle and suspension systems, fifth wheels, coupling devices, kingpins, landing gear and suspension systems for trucks, buses and tractors. Its products are sold and serviced under the SAF, Holland, Neway and SAF-Holland Original Parts brand names.
