NOTICE
The deep snow and mud option is intended to be
used under specific slippery conditions that re-
quire momentary increased wheel spin. Using
this option for an extended period of time may
damage the brake system.
Engine Brake Switch
The Hi/Med/Lo engine brake 3-position switch con-
trols the amount of engine braking. Press the lower
third of the switch for low, center for medium, and
upper third for high. See
Fig. 5.14.
Parking Brake Control Valve
NOTICE
Do not step on the service brake pedal while the
parking brakes are applied. To do so can cause
damage to the brake mechanisms.
The yellow diamond-shaped knob operates the park-
ing brake valve. See
Fig. 5.15. Pull the knob out to
apply the tractor and the trailer spring parking
brakes. Push the knob in to release the spring park-
ing brakes. Before the spring parking brakes can be
released, the air pressure in either air brake system
must be at least 65 psi (447 kPa).
If the trailer is not equipped with spring parking
brakes, pull the parking brake valve out to apply the
tractor parking brakes and the trailer service brakes.
Trailer Air Supply Valve
The red octagonal-shaped knob operates the trailer
air supply valve, which charges the trailer air supply
system and releases the trailer spring parking
brakes. See
Fig. 5.15.
After the vehicle and its air hoses are connected to a
trailer and the pressure in the air system is at least
65 psi (447 kPa), push the trailer air supply valve
knob in (and leave it in) to charge the trailer air sup-
ply system and release the trailer spring parking
brakes. Pull the trailer air supply valve out before
disconnecting a trailer or when operating a vehicle
without a trailer.
Trailer Brake Lever
The trailer brake lever is used to apply the trailer ser-
vice brakes without applying the truck or tractor ser-
vice brakes. It is usually mounted on the right-hand
control panel. See
Fig. 5.16. The valve can be par-
tially or fully applied, but in any partially on position it
will be overridden by a full application of the service
brake pedal. Move the lever down to apply the trailer
brakes; move the lever up to release the trailer
f61118004/24/2012
Fig. 5.13, ATC Switch
f61117606/04/2012
Fig. 5.14, Engine Brake Switch
f610291
1
2
03/10/99
1. Trailer Air Supply Valve (red knob)
2. Parking Brake Control Valve (yellow knob)
Fig. 5.15, Brake Valve Control Knobs
Driver Controls
5.9
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