PART 7: STARTING & OPERATING THE VEHICLE
Manually Releasing Spring Brakes
• To release the full combination of brakes, push in
BOTH yellow and red knobs.
Trailer Air Supply Valve
The red octagon knob controls the air supply to the trailer.
To supply air to the trailer system and release the trailer
parking brakes:
• Allow the tractor air system pressure to build up to
operating level.
• Push the red knob in.
• Hold the red knob in by hand until the trailer air pres-
sure builds to a pre-set level, about 45 psi. At this point
it will remain in.
The yellow knob will remain out; the tractor will remain
parked. If you ever have a failure or disconnect of the air
supply hose to the trailer, the trailer parking brakes will set.
The red knob will automatically pop out and seal off the
tractor air reservoirs to protect the tractor air system pres-
sure. When operating the tractor “bobtail”: The red knob
must remain out to protect the tractor air system pressure
Manually Releasing Spring Brakes
There may be an occasion when you need to tow the vehi-
cle but the air system does not produce enough operating
pressure to release the parking brakes. For these situa-
tions, the spring brakes may be manually released to allow
the vehicle to be towed. This sections details how to re-
lease a drum or an air disc brake.
WARNING!
• Do not operate a vehicle when the spring
brakes have been released manually. Driv-
ing a vehicle that has had its spring brakes
manually released is extremely dangerous.
You would probably have no brakes at all.
You could have a serious or fatal accident.
• Releasing the spring brakes on an unsecured
vehicle could lead to an accident. The truck
could roll, causing severe injury. Always se-
cure the truck with wheel chocks, chains, or
other safe means to prevent rolling before
manually releasing the spring brakes.
R(08/07)
Y53-6015
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Summary of Contents for Peterbilt 320
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Page 210: ...PART 11 SUBJECT INDEX Windshield Washer Reservoir 29 206 Y53 6015 R 08 07 ...
Page 212: ...Peterbilt Motors Company P O Box 90208 Denton Texas 76202 ...