What? Running-in a new trailer? You gotta be joking! Man, that's for grandpa's garage. In fact, truckers will tell you that providing you are using the correctly specified lubricant, you should work a new truck engine hard for the bedding-in process to take place properly. So what's this about running in a new trailer? FleetWatch technical correspondent Dave Scott, says it's the right thing to do.

Nobody nowadays even talks of taking it easy with a new car let alone a truck but it is a real fact that a trailer needs a thorough going-over after the first mission as everything beds down under load. Who is to say that the new trailer manufacturer ensured accurate and correct torque setting during the trailer's construction?

Missing a trailer run-in service impacts on the rest of a trailer's life and that includes a roll-on effect on the prime-mover's performance.The key aspect for trailers is the great variety of torque settings.Insufficient torque leads to loosening parts that finally reflect in accelerated costly tyre wear, seal failure and misaligned trailer suspensions.

Over-torque trailer fittings and stress manifests early in a trailer's life with component failures where excessive torque is applied. Apart from safety compromises, this all works its way into higher fuel consumption.

Trailer durability depends on maintaining the torque settings for fastening suspensions and other components during manufacture. There are as many as 21 torque-settings for a semi-trailer requiring checking after 5 000km under full load when a trailer starts to bed down. The torque required ranges from 1 200Nm for a kingpin nut to 1 000Nm for an axle bolt and down to 10Nm for a hub cap.

Trailer wheel fastening systems need checking much earlier than 5 000km. There's a massive difference between the standard SA trailer stud-mounted rim and the modern hub-mounted rims found on new trucks from Europe and Japan. Stud-mounts require 540Nm and hub-mounts 650Nm. Has anyone out there got a calibrated torque wrench?

Trailer expert Wolfgang Lehmann comments: "Trailer maintenance requires a torque wrench that can handle 1 000Nm - preferably a 400Nm torque wrench with a multiplier that is not as unwieldy as a straight 1 000Nm wrench."

He adds a vital tip: "Rim-mating surfaces must be free of excessive paint that can act as a barrier to correct torque application. Enthusiastically-applied paint on rim-mating surfaces lets wheel lugs come loose under pressure and heat on the road."

And he concludes: "After 5 000kms, trailer suspension clamping bolts and the axle/suspension centre bolt must be checked to 800Nm. Failure to maintain this torque can lead to spring-pack failure.

And don't overlook spring-brake boosters. The quote from the FleetWatch May 2009 article 'Released for mission - accidently or on purpose' is worth repeating:

Without correct mounting bolt torques, any spring-brake non-pressure housing is prone to cracking due to vibration. WABCO Automotive SA specifies that mounting bolts be tightened to 210 Nm torque per mounting bolt and failure to observe this is where the whole booster unit is seen to rip out and fall off. Why? It's simply because most workshops are not equipped with a maximum-rated 350Nm torque wrench and extension piece and the task cannot be carried out without the extension fitting as there's just not enough space in there to tighten down the mounting bolts with the torque wrench alone. So spring-brake actuators are mostly fastened by feel and that's just not enough apart from being too variable.

Finally, a brand new truck can experience extreme driveline wear during its run-in period if trailer couplings are worn beyond acceptable tolerance limits. Excessive play in a trailer coupling causes transmission backlash that leads to early failure.

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