A manual transmission is one of the most efficient ways to get power to the ground from an engine. With the simplicity of selectable gear reduction and the ability to control power to the transmission through a clutch system, a driver has ultimate control over how to deliver the engine’s power to the ground. Also, the efficiency of a solid connection between the engine and the transmission gives the bonus of fuel efficiency that is sacrificed with a torque converter-driven automatic unit. The only downside is that the driver must possess the skills and coordination to operate the shifter and clutch pedal!
The RAM division of FCA (now Stellantis) has taken the old school manual transmission and added a new generation twist to it. The M40MTA transmission is a manual gearbox with a bolt-on assembly that controls shifting and clutch operation. It is found in the RAM ProMaster vehicles behind the 3.0L Iveco diesel motor. In a nutshell, it’s a manual gearbox that comes with a computer-controlled robot that handles transmission shifting and clutch operation for you! Let’s take a closer look at this unit.
THE UNIT
The M40MTA transmission is a conventional 6-speed manual transmission with a single, dry disc clutch assembly controlled by a hydromechanical assembly. No internal modifications were made to the internal gearbox to accept the automated control system.
The hydromechanical assembly is called the Mechanical Transmission Automization (MTA) system. The MTA system consists of the hydromechanical assembly and a Transmission Control Unit. The MTA control is a bolt-on assembly. Clutch actuation is a part of the control system as well. It’s designed to give the advantages of a manual transmission while providing the convenience, efficiency, and reliability of automated operation, preventing driver error and fatigue.
THE COMPONENTS
The main part of the MTA system is the Electrohydraulic assembly (figure 1). It consists of three major components:
- Power unit
- Solenoid Valve Unit
- Gear Control Mechanical Unit
The Power unit houses the oil pump, reservoir, accumulator and pressure sensor. The Power unit generates all the needed pressure to operate the shifter and clutch actuation components. Hydraulic pressure is stored in the accumulator. The accumulator is a sealed nitrogen-charged assembly. Pump flow works against the pressure in the accumulator to fill it. The pump is driven by an electric motor that is commanded on and off by the TCU. Fluid pressure is kept between 522 and 667 psi. The TCU uses feedback from the pressure sensor to maintain this range so that the pump doesn’t run continuously.
The Solenoid Valve Unit houses 4 PWM solenoids that operate the shifter and clutch assemblies (figure 2). EV0 operates the clutch master/slave system. EV1, EV2, and EV3 are responsible for the shifter operation. The solenoids are fired in sequence to move the shifter through the gate to the gear selected by the TCU. The solenoids each direct oil to the Control Manifold to operate plunger valves that physically move the shifter. EV1 and EV2 function to engage and disengage gears. EV3 functions as a selector and works against opposing pressure from a spring assembly that pushes the selector mechanism toward the reverse selection gate in Neutral (figure 3). EV3 must be energized and functioning to select all ranges except Reverse.
The Gear Control Mechanical Unit houses 2 linear differential transformer sensors, the interface lever, engagement, and selection pistons. The interface lever, engagement piston, and selection piston act as the ‘hand’ that shifts the transmission internally. Together, they respond to the commands of the TCU, and the pistons from the PWM solenoids move them accordingly. Two linear differential transformer sensors are position sensors that provide feedback to the TCU to verify that the commanded shift sequence occurred correctly.
SERVICING
Aside from the pressure sensor and hydraulic lines, the MTA unit is serviced and sold as an assembly. More parts may become available for replacement as these units age. The gearbox assembly uses gear lube. The recommended fluid is a synthetic 75W 85 (Mopar part number 68083381, 2.9 qts.) No service interval is given for this.
The clutch and pressure plate assembly is serviced similarly to convention units. The M40MTA uses a dual-mass flywheel which, of course, can be pricey if replacement is needed. Prior to servicing the clutch and/or flywheel, you must go through the Hydraulic Circuit Depressurization routine for the MTA system. This process is scanner-driven. Therefore, you must have a scan tool capable of accessing this function.
The Hydraulic Circuit Depressurization routine is as follows:
- Remove the turbocharger air inlet hose.
- Fill the clutch fluid reservoir.
- Properly connect a pressure bleeder to the fluid reservoir.
- Remove the protective cap at the bleeder port.
- Connect a hose to control the discharge of fluid at the bleeder port into an appropriate container.
- Open the bleeder port until there is a solid stream of fluid with no indication of air coming out of the port.
- Close the bleeder port.
- Remove the discharge hose from the bleeder port and reinstall the protective cap.
- Remove the pressure bleeding equipment.
- Correct the fluid level in the clutch fluid reservoir.
- Install the turbocharger air inlet hose.
- Connect the scan tool.
- Navigate to the bleed procedure.
- Follow the prompts on the scan tool.
Servicing or replacing the hydromechanical unit may require depressurization of the system as well. The following repair operations require the depressurization of the MTA system prior to disassembly:
- Pressure sensor
- Temperature sensor
- Pressure control valve
- Flow control valve
- Hydraulic lines
- Clutch actuator
- Control unit
After any of these components have been serviced, there is a proper order for bleeding the system depending on which components were serviced. There is also a relearn and a reset that must be done as well for proper operation. Note that the pressure inside the MTA hydraulic system can be as high as 1,000 psi. Do not attempt to work on this system until you verify that the depressurization process is completed.
Automotive engineers have created yet another marvel with an emphasis on keeping things as simple as practical. With the coverage that this unit has already around the world, there leaves no doubt that this transmission will be with us for many years to come. It leaves us technicians and diagnosticians a new set of challenges to track in the future!
