POWER TRAIN -726250059

TM 9-2320-364-34-1

a. Engine. The truck is equipped with a Detroit Diesel Corporation (DDC) Model 8V92TA engine rated at

500 HP. The drive train control system consists of the engine and transmission systems.

(1) The DDEC II and DDEC III/IV contain a microprocessor-based electronic control module to regulate the

electronic distributor unit. This distributor unit controls the individual or unit injectors that regulate both the amount

and timing of fuel delivery. The DDEC II and DDEC III/IV electronically govern engine speed and can be

programmed to accommodate truck configuration changes. The DDEC II and DDEC III/IV are electronically linked

with the transmission, through the ATEC, to improve truck performance.

(2) The DDEC and ATEC systems perform self diagnostics, engine/transmission system diagnostics and

truck performance diagnostics. Self diagnostics includes personnel initiated checks of main electronic components

such as solenoids, wiring, sensors and control modules. System diagnostics monitor critical engine and transmission

parameters such as oil temperature, oil pressure, coolant temperature, voltage and gear range attained. Truck

performance diagnostic capabilities aid the mechanic in isolating problems outside of the electronic control system.

Operating data is stored in the DDEC II's and DDEC III's memory for display at a later time. Stored data includes

total engine hours and fuel consumed. The DDEC also tracks intermittent problems by logging the number of

occurrences and the engine hours of each occurrence.

b. Transmission. The truck uses an Allison 700 Series Transmission, Model CLT-755. This hydro-kinetic type

transmission has an integral-locking torque converter, lock-up clutch, constant mesh planetary gearing, the ATEC, a

speedometer and a control valve body assembly.

(1) The Electronic Control Unit (ECU), which contains the microprocessor based electronics, is located in a

protected area within the truck. The ECU receives information, in the form of signals from switches and sensors,

processes the information and sends electrical signals to the appropriate solenoids which control the transmission

operation. The ECU features diagnostics which can sense many electronic system malfunctions and identify them

with a displayed code. The ECU also protects the transmission from cold weather start-ups by inhibiting normal

shifting functions until a minimum sump oil temperature of 20 degrees F (- 7 degrees C) is attained.

(a) The CHECK TRANS light alerts the operator, momentarily, every time the system is activated, as a

lamp check, and/or when the ECU finds a problem in the system. If the check transmission light comes on, the

problem is minor. In most cases, the transmission will continue to operate in a normal manner. However, in some

cases the ECU will take action to reduce the possibility of damage to the truck or the transmission. The transmission

should be serviced at the next opportunity.

(b) The DO NOT SHIFT light and/or buzzer alerts the operator, momentarily, every time the system is

activated as a lamp check and any time the ECU has detected a more severe problem in the system. The ECU will

cause the transmission to hold-in-gear and disengage the lock-up clutch.

(2) The push button range selector is totally electronic. Range selection is achieved by means of seven snap

dome switches. To select a range, touch the pad. The pad will light up, a beep will be heard and a "click" will be felt.

The transmission will be ready to operate in the selected range. The range selector also has a "DO NOT SHIFT" light

and a warning tone or buzzer.

(a) Select the Drive position and the truck will start in first (low range only) or second range and

automatically upshift to a higher range as output speed increases. As the truck slows down, output speed decreases

and the transmission automatically downshifts to the correct range. If a locked brake or a slick-surface condition

should occur, the ECU will command converter operation and inhibit downshifts for a period of time or until normal

wheel speed has been restored. Drive (4) should be selected for moderate loads, grades and over-the-road operation

with restrictive speed limits. Drive (3) is appropriate for operating in rough terrain or in heavy traffic. Drive (2)

should be selected when need for speed control requires a second gear hold condition such as descending steep grades

where additional engine braking is required, for operation on rough terrain, or greater retarder action. Selecting

Drive (1) permits the driver to operate the truck in areas where maximum performance in extremely rough terrain is

required.

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