Tractor-trailer connections have a lot of variables, but one constant is the need for a sturdy and safe connection. No one wants a trailer to disconnect from a tractor going down the road or making a turn.
In addition to the physical connection, there must also be electrical connection between the tractor and trailer for lights, along with air connections for brakes and in many cases suspension. These connections must be able to be disconnected without much hassle, yet maintain a reliable connection when the vehicle is in operation.
This is where fifth wheels and connections like gladhands come into play. A fifth wheel is the system that mechanically attaches the trailer to the tractor. In broad terms, it functions by having a king pin on the trailer sliding in a channel on a plate that is mounted on the trailer and being locked in place. The king pin rotates in the plate, which is stationary.
Fifth wheels typically consist of a slide plate, base plate, mounting components, a stop, the throat, coupling/locking components, a handle for operation, and the king pin on the trailer. Many modern fifth wheels can be disengaged by the truck’s brake system’s air supply and in-cab air releases.
To ensure they are functioning properly, fifth wheels require regular inspection and maintenance/lubrication. Technicians can save time and be sure they are covering all the necessary steps by using a resource like Mitchell 1’s TruckSeries truck repair information software which provides the maintenance, inspection and repair procedures techs need to keep fifth wheels in good operating condition. (See Figure 1 for a sample of fifth wheel service information in TruckSeries – click to expand image to full size).
Figure 1
It’s also important to consider the connections for electrical and air for towing a trailer. The air hose connections between a truck and a trailer are commonly called gladhands. These got their name because they resemble two hands clasping. The gladhands are specific in color for their function, with red supplying air to emergency brakes and blue for service lines — standards that are specified in SAE J318. These have differences so they cannot be connected to each other. See Figure 2 below, showing two different types of gladhands.
Figure 2
One major benefit from gladhands is the ability to disconnect without using tools. The electrical connection used between tractors and trailers is a 7-way round pin connector. The pins are number and color coded. These connector standards are specified in SAE J560 and were implemented in 1951. Both of these types of connectors should be inspected for defects on a regular basis. (Figure 3 shows SAE J560 7-way trailer connector pin identification in Mitchell 1’s TruckSeries – click to expand image to full size.)
Figure 3
Fifth wheels have been an integral part of the trucking industry since the patent was submitted for automotive applications way back in 1915. As trucking and automotive technology evolved, air hose and electrical connections were needed. Gladhands and 7-way connectors eventually filled these needs. Today’s tractor-trailers have reliable and safe connections for all these, and with proper maintenance will function safely throughout the life of the vehicle.
Additional tips for repair and maintenance of Class 4-8 trucks may be found in the Mitchell 1 ShopConnection Truck blog: https://mitchell1.com/shopconnection/category/truck