RE4RO3A Transmission |
Source: scottmeister at Patrol4x4.com
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The RE4R03A is an electronically controlled transmission. That is, a separate transmission control unit (TCU) is required to facilitate transmission operation. This TCU determines the optimal shift timing based on input data from various sensors (i.e. vehicle speed, engine speed, throttle position).
It also modulates the hydraulic pressure supplied to the clutch packs through pulse width modulation (PWM) of the line pressure solenoid, and applies torque converter lock-up based on various criteria (shifter selection, vehicle speed and TPS position, namely). The figure below illustrates the basics of the control system.
It also modulates the hydraulic pressure supplied to the clutch packs through pulse width modulation (PWM) of the line pressure solenoid, and applies torque converter lock-up based on various criteria (shifter selection, vehicle speed and TPS position, namely). The figure below illustrates the basics of the control system.
The TCU's principal means of control is via five solenoids located on the valvebody:
• Torque converter clutch solenoid valve. This clutch locks the turbine and impeller of the torque converter together;
• Shift solenoid valve A and B. These determine which gear is selected by altering the route of hydraulic pressure through the valvebody;
• Overrun clutch solenoid, which allows engine braking to occur by locking the front planetary carrier with the rear internal gear; and the
• Line pressure solenoid, which through the dropping resistor, is pulse width modulated to determine the pressure generated by the oil pump. Minimising the pressure generated at light loads reduces the pumping losses incurred by the transmission.
When in ‘D’ mode, the selected gear is determined based on the activation of the two shift solenoids by the TCU. The solenoids, located on the valvebody, determine to which locations the hydraulic pressure is supplied.
• 1st gear = Shift solenoid A and B active;
• 2nd gear = Shift solenoid B only active;
• 3rd gear = Shift solenoid A and B inactive; and
• 4th gear = Shift solenoid A only active.
• Torque converter clutch solenoid valve. This clutch locks the turbine and impeller of the torque converter together;
• Shift solenoid valve A and B. These determine which gear is selected by altering the route of hydraulic pressure through the valvebody;
• Overrun clutch solenoid, which allows engine braking to occur by locking the front planetary carrier with the rear internal gear; and the
• Line pressure solenoid, which through the dropping resistor, is pulse width modulated to determine the pressure generated by the oil pump. Minimising the pressure generated at light loads reduces the pumping losses incurred by the transmission.
When in ‘D’ mode, the selected gear is determined based on the activation of the two shift solenoids by the TCU. The solenoids, located on the valvebody, determine to which locations the hydraulic pressure is supplied.
• 1st gear = Shift solenoid A and B active;
• 2nd gear = Shift solenoid B only active;
• 3rd gear = Shift solenoid A and B inactive; and
• 4th gear = Shift solenoid A only active.
One can see from the above combinations that limp mode means neither of the solenoids will be active, and thus only 3rd gear may be used.
The TCU will also activate the overrun clutch and torque converter lockup as necessary. For all gear shifter positions (which controls the "manual valve" in the valvebody), the valvebody has different circuits to alter slightly how the transmission operates. These functions are seen in the figure below.
The TCU will also activate the overrun clutch and torque converter lockup as necessary. For all gear shifter positions (which controls the "manual valve" in the valvebody), the valvebody has different circuits to alter slightly how the transmission operates. These functions are seen in the figure below.
From the figure above it is obvious that holding the transmission in "1" or "2" has some differences to when the transmission is in "D". Most notably in "1", the overrun clutch is always engaged, maximising engine braking under all throttle conditions. The overrun clutch is only usually enabled in "D" when the power button is on, or O/D is off, and even still only at light throttle positions. The cutaway below shows the position of the major components within the transmission we are concerned with.
All RE4R03A transmission variants are fundamentally similar in the key mechanical design. However, some models, particularly those used in 2wd road going vehicles, have a slightly different gearing particularly 1st gear. In most variants 1st gear is approximately 2.784:1, whereas in these other variants 1st gear is around 2.584:1. Obviously this taller 1st gear is not desirable for 4wd applications. These 2wd versions also have a different rear housing which is not designed for coupling with a transfer case.
There should be a metal tag attached to the transmission which will tell you the serial number and transmission code. The table below shows a selection of transmission codes and a corresponding selection of information I have gleaned from several different FSMs.
There should be a metal tag attached to the transmission which will tell you the serial number and transmission code. The table below shows a selection of transmission codes and a corresponding selection of information I have gleaned from several different FSMs.
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