Instruments and Controls Identification Fifth Wheel Air Slider Control Valve Switch, Optional Air-Operated Sliding Fifth Wheel Controlled Traction Differential Control Valve Switch On vehicles equipped with an Eaton single-drive rear axle, a controlled traction differential feature is stan- dard. A control valve switch ( Fig. 2.13 ) engages and disengages the controlled traction feature. A guard is positioned around the switch to prevent it from being accidentally activated. WARNING Do not activate the fifth wheel air slider control valve when the vehicle is in motion. Doing so could result in damage to the fifth wheel member, kingpin, cab, or trailer, and ultimately, to the driv- etrain.
A guard is positioned around the switch to prevent it from being accidentally activated. See Chapter 9 for complete operating instructions. The fifth wheel air slider valve permits repositioning of the sliding fifth wheel from inside of the cab. Mov- ing the air slider control valve switch ( Fig. 2.12 ) to the lock position deactivates the control valve and locks the fifth wheel to the baseplate. Moving the switch to the unlock position activates the control valve and unlocks the fifth wheel slide mechanism, allowing changes to the total length of the tractor- trailer and changes to axle loads, to comply with varying state or provincial laws.
A red indicator light, if so equipped, is illuminated whenever the fifth wheel slider is unlocked. Parking Brake Control Valve and Trailer Air Supply Valve f600307 10/04/93 Fig. 2.13, Controlled Traction Differential Control Valve Switch The yellow diamond-shaped knob ( Fig. 2.12 ) oper- ates the parking brake valve. Pull the knob out to apply both the tractor and the trailer spring parking brakes. Push the knob in to release the tractor spring parking brakes. Before the spring parking brakes can be released, the air pressure in either air brake sys- tem must be at least 65 psi (447 kPa).
Air Suspension Dump Valve, Optional The air suspension dump valve allows the air in the vehicle air suspension to be quickly exhausted, low- ering the rear of the vehicle. This makes it easier to connect to or disconnect from a trailer. A control valve switch ( Fig. 2.14 ) exhausts and fills the air sus- pension. To exhaust air from the suspension, move the switch to LOWER. A guard is positioned around the switch to prevent it from being accidentally activated. The red octagonal-shaped knob ( Fig. 2.12 ) operates the trailer air supply valve.
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 (it should stay in) to charge the trailer air supply system and release the trailer spring parking brakes. Before disconnect- ing a trailer, or when operating a vehicle without a trailer, pull the trailer air supply valve knob out. CAUTION Never exhaust air from the suspension while driving. If the air is exhausted, the suspension will not absorb road shocks and could be dam- aged. See Chapter 6 , under the heading "Brake System," for instructions regarding use of the trailer air supply valve and parking brake valve. 2.10