OM3223 Operation - Section 32 Operator Cab and Controls Page 32-3 SERVICE BRAKE PEDAL Service brake pedal (2, Figure 32-4) is a foot-oper- ated pedal which applies the service brakes. THROTTLE PEDAL Throttle pedal (4, Figure 32-4) is a foot-operated pedal which allows the operator to control engine rpm, depending on pedal angle. NOTE: In some optional installations, this pedal may not be present, because it is incorporated into a single pedal function with retarder pedal (3). DYNAMIC RETARDER PEDAL Dynamic retarder pedal (3, Figure 32-4) is a foot- operated pedal which allows the operator to slow the truck and maintain a safe productive speed without the use of the service brakes.
For normal truck oper- ation, only dynamic retarding is to be used to slow and control the speed of the truck. Grade/speed chart (8, Figure 32-1) is to be followed to determine maximum safe truck speeds for descending various grades with a loaded truck. Service brakes are to be applied only when dynamic retarding requires addi- tional braking force to slow the truck speed quickly and to bring the truck to a complete stop. FIGURE 32-4. PEDALS 1.Cab Floor 2.Service Brake Pedal 3.Retarder Pedal 4.Throttle / Accelerator When dynamic retarding is in operation, the engine rpm will automatically go to an advance rpm retard speed setting (usually 1250 RPM)*.
Dynamic retard- ing will be applied automatically, if the speed of the truck reaches the predetermined overspeed retard setting. Dynamic retarding is available in forward/ reverse at all truck speeds above 0 kph/mph, but is available in NEUTRAL only when truck speed is above 4.8 kph (3 mph). HEATER / AIR CONDITIONER VENTS The operator has complete control of the air flow in the cab. Heater/air conditioner vents (5, Figure 32-1) are flapper type which may be individually opened or closed and may be rotated 360° for optimum air flow. There are four (three not shown) across the top of the panel, two in front of the operator (one each in right and left panel modules), and four below the panel.
* NOTE: The exact engine speed in retarding may vary (1250 - 1650 rpm) due to the temperature of certain components; this is controlled by the Statex III control system. Optional - Dual Function / Single Pedal The dynamic retarding/brake pedal is a single foot- operated pedal which controls both retarding and service brake functions. Thus, the operator must first apply, and maintain, full dynamic retarding in order to apply the service brakes. When the pedal is partially depressed, the dynamic retarding is actuated (actuation is modulated).
As the pedal is further depressed, dynamic retarding is fully applied; then, while maintaining full retarding, the service brakes are actuated (a slight increase in pedal resistance will be felt) through a hydraulic valve, which modulates pressure to the service brakes. Completely depressing the pedal causes full application of both dynamic retarding and the service brakes.