It is sometimes assumed that the fifth wheel is a ‘set and forget’ component, but in actual fact it should be inspected, lubricated and, if necessary, adjusted at least every three months or 40,000km, whichever comes first, you really need to keep your fifth wheel in peak condition.
It stands to reason that the fifth wheel, the device that connects a semi-trailer or trailer combination to the prime mover, should be front-of-mind for truck operators in the interests of safety for themselves and other road users.
As such, a regular service and inspection regime is critical to ensure smooth and safe operation. Possessing a robust and durable design, with a small amount of care and attention the average fifth wheel will last for many years. Of course, units operating in harsh outback conditions on dusty roads will require considerably more attention than those working under ideal conditions, such as interstate highway running.
Unlike earlier ‘greasy plate’ units, modern fifth wheels are available with replaceable non-metallic inserts on the plate which negates the need for lubrication. However, lubrication between the king pin and jaw is still vital and is done either manually via the grease nipple on the side of the plate or by an automatic greasing system.
Since the kingpin and jaw bear the articulation and acceleration forces between the prime mover and trailer, over time wear will occur in these components, necessitating adjustment to take up the slack.
As National Training Manager for JOST Australia and having started his career as a truck mechanic, Bob Martin knows a thing or two about keeping fifth wheels in tip-top shape.
Bob explains that the checking and adjustment procedures for JOST’s most popular fifth wheel ranges, the JSK36 and JSK37, are relatively simple, and best accomplished using two JOST service tools.
The first tool incorporates a pseudo kingpin which the jaw locks onto, simulating a coupled status.
“It’s important to ensure the tool is sitting squarely on the plate, which means on top of the greaseless inserts at three points, if these are fitted,” says Bob.
With the tool installed, two 24mm spanners are used to loosen the locknut and adjusting bolt located on the side of the plate, with the bolt then unscrewed several turns until it’s loose.
“This allows the locking bar to come all the way in against the lock jaw,” says Bob.
The next step involves turning the adjusting bolt clockwise by hand until resistance is felt, which means the bolt has come into contact with the end of the lock bar.
“From that position we wind the adjusting bolt in a further one-and-a-half turns, then hold the bolt with one spanner and tighten the locknut with the other,” says Bob, adding that this is the end of the jaw adjustment procedure.
The other fifth wheel maintenance tool that JOST has developed is the jaw checking tool which allows the technician to determine if the jaw has worn to the point where it needs to be replaced. It is a double ended tool with one end suitable for the JSK36 and the other for the JSK37.
“The idea is that if the gauge slips over the jaw then the jaw is worn out and must be replaced,” says Bob. “With the fifth wheel in the locked position, we push the jaw forward and try to fit the tool onto the jaw in the rear most position which is where the wear occurs. If the tool doesn’t slide onto the jaw then it is still in a serviceable condition.”
