Allison 1000/2000/2400 Series transmissions are torque converter driven fully automatic units. All models have neutral, reverse, and up to 5 forward speeds, with 5th gear being overdrive. Refer to Figure 2 for the different gears ratios available in the different models.
The torque converter housings of these units mate directly to SAE No. 2, SAE No. 3, or direct to the engine block in some cases. Flexplate drive is used for all engine to transmission torque transfer.
Several different torque converters are available to match the transmissions to a wide variety of diesel and gasoline engines. The torque converter is a single stage, three element unit, consisting of a pump, stator, and turbine, with the addition of a converter clutch to provide direct drive from the engine to the transmission. The converter clutch is applied and released electronically, and changes the direction of fluid flow in the converter as in most typical converters today.
Internally these units contain 2 rotating clutches (C1 and C2), and 3 brake clutches (C3, C4 and C5), to direct the flow of torque through the unit. All clutch packs are hydraulically applied and spring released, with automatic wear compensation, and their locations in the transmission are shown in the cutaway in Figure 2.
The Transmission Control Module (TCM) signals six different solenoids, located on the valve body, to apply and release clutches based on vehicle speed and power combinations, and the range selected by the operator.
The planetary gear train consists of three constant mesh, helical gear planetary sets, refered to as P1, P2, and P3. By the engagement of the 5 clutch packs in various combinations, the planetary gear sets react singly or together to provide 5 forward speeds, neutral, and reverse.
A common hydraulic system provides fluid for all hydraulic operations, lubrication, and cooling. The front oil pump, driven by the converter, provides the pressure needed for the hydraulic system, and comes from the common sump in the bottom pan.
A suction filter, located in the bottom pan provides general protection to the entire hydraulic system, and a spin-on filter provides full time protection for the control solenoids and multipass protection for the entire system.
The spin-on filter is located externally on the converter housing at the lower left front of the transmission.
Some 1000/2000/2400 Series transmissions are available with an optional extension housing that accommodates an OEM installed two shoe, expanding type, drum parking brake.
The 1000/2000/2400 Series transmissions use lever type shift selectors, as shown in Figure 4. The vehicle may be equipped with one or two shift selectors, depending on the number of operator stations for driving the vehicle and/or operating a variety of chassis mounted equipment. The shift positions on the shift selector can vary according to the shift selector installed in the vehicle.
Managing the Vehicle Damage Repair Process
In the event that your vehicle requires damage repairs, GM recommends that you take an active role in its repair. If you have a pre-determined repair facility of choice, take your vehicle there, or have it towed there. Specify to the facility that any required replacement collision parts be original equipment parts, either new Genuine GM parts or recycled original GM parts. Remember, recycled parts will not be covered by your GM vehicle warranty.
Insurance pays the bill for the repair, but you must live with the repair. Depending on your policy limits, your insurance company may initially value the repair using aftermarket parts. Discuss this with your repair professional, and insist on Genuine GM parts. Remember if your vehicle is leased you may be obligated to have the vehicle repaired with Genuine GM parts, even if your insurance coverage does not pay the full cost.
If another party’s insurance company is paying for the repairs, you are not obligated to accept a repair valuation based on that insurance company’s collision policy repair limits, as you have no contractual limits with that company. In such cases, you can have control of the repair and parts choices as long as cost stays within reasonable limits.
The electronic control of the transmission is performed by the Transmission Control Module (TCM). Transmissin Control Modules are available in both 12V and 24V configurations, to match the configuration of the vehicle electrical system.
The TCM, shown in Figure 6, recieves and processes signals from various switches and sensors. The TCM determines shift sequences, shift timing, and clutch apply and release pressures. The TCM uses this information to control solenoids and valves, supply system status, and provide diagnostic information for service technicians.
EXTERNAL COMPONENTS SPEED SENSORS
The speed sensors are variable reluctance devices which convert mechanical motion to an AC voltage. Each sensor consists of a wire coil wrapped around a pole piece that is adjacent to a permanent magnet. These elements are contained in a housing which is mounted adjacent to a rotating ferrous member, such as a gear tooth. Two signal wires extend from one end of the housing and an exposed end of the pole piece is at the opposite end of the housing. As a ferrous object, such as a gear tooth approaches and passes through the gap at the end of the pole piece, an AC voltage pulse is induced in the wire coil. The TCM calculates the frequency of these AC pulses and converts it to a speed value. The AC voltage generated varies from 150mV at low speed to 15V at high speed. The signal wires from the sensor are formed as twisted pairs to cancel magnetically induced fields. The cable is also shielded to protect from voltage-related fields. The typical speed sensor is shown in Figure 7. Noise from other sources is eliminated by using two-wire differential inputs at the TCM.