During initial starting, the hydraulic system pressure gage can read as high as
2,200 psi (15,169 kPa). As the APU runs/warms up, pressure ranges will start and
continue to decrease. Do not operate the hydraulic controls until the APU has had
time to warm up or damage to equipment may result.
p. Allow APU to run for 20 minutes. If outside temperatures range from -25F to 50F (-31C to 46C), filter
indicator and hydraulic pressure gages will not approach normal operating parameters until semitrailer has been
pulled/towed for a couple of hours. Periodically check that pressure gage and filter indicators are approaching
normal conditions. If indicators gradually decrease/return to normal operating ranges, APU is ready for normal
q. Perform step i of paragraph 2-30 to disconnect and stow APU jump start cables.
OPERATION ON GRADES
Because of the length of the tractor/semitrailer combination, one or more bogies
will be lifted off of the ground when approaching or cresting a grade which is more
than 15 percent. The semitrailer suspension must be adjusted during these
operations to ensure that all bogies maintain contact with the ground. This
provides better stability when the semitrailer is loaded and reduces strain on the
platform and suspension.
Maximum grade for fully loaded semitrailer is 20 percent. Grades up to 30 percent
may be negotiated, provided the payload does not exceed 50,000 pounds (22,700
kg). Do not exceed 30 percent grade. Exceeding these limitations may cause
serious damage to the semitrailer.
a. Approaching an uphill grade.
(1) Stop tractor/semitrailer combination before reaching grade.
(2) Lower platform (para. 2-19) to minimum suggested height (1 inch of suspension cylinder plunger/piston
(3) Pull onto grade.