How to Break in a New Trailer

To ensure proper operation and a long life, new trailers should get particularly close attention during the first 30 days of their service life. While operations maintenance records will reflect all areas that should be closely checked, the following checklist recommends chassis areas to which you should pay close attention.

Tires

Preventive maintenance mechanics should be alert for under inflated tires and threaded fasteners that may have loosened from factory-torque settings. While a new trailer's tires were correctly when they were mounted at the factory, tire pressure is related to ambient temperature at inflation time. If a new trailer had tires mounted in a 70° ambient environment, but was put into service in 20° weather; the tires may have lost as much as 10 psi for every drop of 20° in ambient temperatures below 50°. Therefore, all tire pressures should be verified with a tire gauge, and rechecked each time the tractor fuels.

Wheels

Smaller fleets commonly over-look the need to retighten new trailer wheel lug nuts after the first 50-100 miles of service on the initial "in-service." Retightening compensates for "normal" clamp force lost due to "seating in" of new materials. Tests have shown new trailer wheel lug nuts lose 250 lb.ft. or about half of their original torque value, during a short period of initial service. Unless these nuts are retighten to spec, additional clamping force will be lost, and disc wheels will eventually wobble to the point where their ball seats become elongated. Retightening during the initial in-service prevents wheel and stud damage. Then, lug nuts should be tightened every 25,000 miles.

Leaf-spring Suspensions

Tandem suspensions are 100% aligned when new trailers leave the factory. However, suspension fasteners can loosen, causing alignment settings to change, and that can translate into possible erratic ride or accelerated tire wear. Therefore, at the first trailer preventive maintenance interval, all suspension-system fasteners should be rechecked for correct torque value. When tightening suspension-system fasteners, mechanics must tighten the "nut side" of torque-arm bolts. Tightening bolt heads does not produce the correct clamping force on bushings. It is also important to keep U-bolts as well as torque-arm bolt tight. Loose U-Bolts allow a trailer axle to shift, and even minor shifting during braking can cause control problems, excessive tire wear and even broken spring leaves. When U-Bolts are torqued to proper spec's, leaf spring main leaves remain in proper contact with wear pads with no "twists". Spring wear-pad contact will then be even, too.

Also, at the first TPM, a trailer mechanic should take the time to verify that there are no obstructions to movement of the suspension equalizer. When the mechanic has made sure all fasteners are tight, he or she should use the 50" tape method, with axle extenders, to verify that the trailer is indeed properly aligned. Remember that the longer the trailer, the more critical tandem alignment is to long tire life.

Air Suspensions

Loose U-bolts in an air suspension can cause a new trailer to roll and sway. Usually a driver is quick to report this condition. The mechanic should make doubly sure that trailer-suspension fasteners, including U-bolts, are properly tensioned. Excessive play in an air suspension's front-pivot connection is another cause of premature tire wear and erratic handling. Again, connection bolts, which may have loosened during the first weeks of service, may such handling problems. If not retightened, these loose bolts cause rubber-bushing wear.

Sliding-tandem Operation

A driver learning to handle a new trailer equipped with a sliding tandem should be sure he knows exactly how to use the stop-selector bar. He should also make sure that all four slider lock pins are set in place before operating the trailer, otherwise the tandem may not be "locked", and a sudden brake application could force the slide rearward, causing damage to the tandem and buck plate.

Air System and Brake Operation

During the first month's operation, a certain amount of "burnishing in" of brake lining occurs. This is normal and may result in some adjustment loss. Because out-of-adjustment trailer brakes means increased stopping distance, plus an increased potential for jackknifing under certain conditions, trailer brakes should be manually readjusted at the first TPM inspection. Note that at the point of sale and during routine maintenance, the dust cover cap on air chambers must be inspected to assure that it is in place and sealing properly.

Doors

Almost invariably, a new trailer's hinged-type doors are difficult to latch. You may want to advise drivers or owners that they should expect to use extra muscle to secure doors until seals seat, but they should not use bars or some other device to force doors shut. It is equally important not to make adjustments to a new trailer's door latches or hinges to "correct" door closing, as this will result in a poor sealing later on.

Washing and Chemicals

Improper use of chemicals cleaners has caused many newly delivered trailers finishes to streak and fade- particularly yellow, red and black models. Ironically, fade is often caused by a desire to keep the units' clean- and using too strong a chemical solution. Sometimes fading is caused by an overly concentrated caustic agent.