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MAINTENANCE TIPS
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REAKING-IN A NEW TRAILER
The most critical time in a new trailer’s life is its initial
i
n-service check and first month’s “shakedown.”
Preventive maintenance mechanics should be alert for
under-inflated tires and threaded fasteners that may
have loosened from factory-torque settings. Fastener
torque should be all-inclusive and include refrigeration
u
nits, tanks, steps, carriers etc.
Following are several areas that deserve particularly
close attention during the first 30 days of a van or
platform trailer’s service life. Of course, your
operation’s maintenance records should reflect all
areas which need to be closely checked.
TIRES
While a new trailer’s tires were correctly inflated 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˚ F. ambient
environment, but was put in service in 20˚ F. weather,
the tires may have lost as much as 10 psi for every
drop of 20˚ F. in ambient temperatures below 50˚ F.
Therefore, all tire pressures should be verified with an
air gauge, and rechecked each time the tractor refuels.
WHEELS
Smaller fleets commonly overlook the need to retighten
new-trailer-wheel lug nuts after the first 50 to 100 mi.
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 those nuts are retightened to
spec, additional clamping force will be lost, and
damage to components will occur. Re-tightening during
the initial in-service prevents wheel and stud damage.
Thereafter, lug nuts should be checked every 25,000 mi.
LEAF-SPRING SUSPENSIONS
All tandem axles are aligned when new trailers leave
the factory. However, suspension fasteners may
sometimes loosen, causing alignment settings to
change, and that can translate into possible erratic
ride, or accelerated tire wear. Therefore, at the first
TPM 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 the fastener.
It is also important to keep U-bolts, as well as torque-arm
bolts, tight. Loose U-bolts allow trailer axles to shift, and
even minor shifting during braking can cause control prob-
lems, excessive tire wear, or even broken spring leaves.
When U-bolts are torqued to proper specs, 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 equalizers.
When the mechanic has made sure all fasteners are
tight, he should use the 50-ft.-tape method, with axle
e
xtenders, to verify that the trailer tandem is, indeed,
properly aligned. Remember: the longer the trailer,
the more critical tandem alignment is to long tire life.
AIR-SPRING SUSPENSIONS
Loose U-bolts in an air-spring 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 tightened.
Excessive play in an air-spring suspension’s front-pivot
connection is another cause of premature tire wear and
erratic handing. Again, connection bolts, which may
have loosened during the first weeks of service, may
produce 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 slider rearward, causing damage to the tandem
and trailer.
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 mean increased stop-
ping distance, plus an increased potential for jackknif-
ing under certain conditions, trailer brake adjustment
should be checked at the first TPM inspection.
During routine maintenance the dust cover cap on air
chambers must be inspected to assure that is in place
and sealing properly.
ANNUAL FHWA INSPECTION
It is the carriers’ responsibility to make sure that the
vehicles operated by them are inspected and main-
tained under this Federal requirement. During this
inspection, make sure the upper slide rail to cross-
member welds, pintle hook assemblies, safety equip-
ment, etc. are inspected and corrected as required.
DOORS
Almost invariably, a new trailer’s hinged-type doors are
difficult to latch. Drivers should expect to use extra
muscle to secure doors until seals seat, but drivers
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. This will result in a poor sealing later on.
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