A/T System Description - General

General Operation

The automatic transmission is a combination of a 3-element torque converter and triple-shaft electronically controlled unit which provides 4 speeds forward and 1 reverse. The entire unit is positioned in line with the engine.

Torque Converter, Gears, and Clutches

The torque converter consists of a pump, turbine, and stator assembly in a single unit. They are connected to the engine crankshaft so they turn together as the engine turns. Around the outside of the torque converter is a ring gear which meshes with the starter pinion when the engine is being started. The entire torque converter assembly serves as flywheel while transmitting power to the transmission mainshaft, the transmission has three parallel shafts; the mainshaft, the countershaft, the secondary shaft. The mainshaft is in line with the engine crankshaft, and includes the 3rd and 4th clutches, and gears for 3rd, 4th, reverse, and idler. The mainshaft reverse gear is integral with the mainshaft 4th gear. The countershaft includes the gears for 1st, 2nd, 3rd, 4th, reverse, park, and the final drive. The final drive gear is integral with the countershaft. The countershaft 4th gear and the countershaft reverse gear can be locked to the countershaft providing the 4th or reverse gear, depending on which way the selector is moved. The secondary shaft includes the 1st and 2nd clutches, and gears for 1st, 2nd, and idler. The idler shaft is located between the mainshaft and secondary shaft, and the idler gear transmits power between the mainshaft and the secondary shaft. The gears on the mainshaft and the secondary shaft are in constant mesh with those on the countershaft. When certain combinations of gears in the transmission are engaged by the clutches, power is transmitted from the mainshaft and the secondary shaft to the countershaft provide [D], [2], [1], and [R] positions.

Electronic Control

The electronic control system consists of the Powertrain Control Module (PCM), sensors, and solenoid valves. Shifting and lock-up are electronically controlled for comfortable driving under all conditions. The PCM is located below the dashboard, behind the glove box.

Hydraulic Control

The valve bodies include the main valve body, the regulator valve body, and the servo body. They are bolted to the torque converter housing. The main valve body contains the manual valve, the shift valves A, B, C, and E, the relief valve, the lock-up control valve, the cooler check valve, the servo control valve, and the ATF pump gears. The regulator valve body contains the regulator valve, the torque converter check valve, lock-up shift valve, and the 1st accumulator. The servo body contains the servo valve, the CPB valve, accumulators for 2nd, 3rd and 4th and shift solenoid valves for A, B, C, and E. Fluid from the regulator passed through the manual valve to the various control valves. The 1st and 3rd clutches receive fluid their respective feed pipes, and the 2nd and the 4th clutches receive fluid from the internal hydraulic circuit.

Shift Control Mechanism

The PCM controls to shift gears the shift solenoid valves A, B, C, and E, and the A/T clutch pressure control solenoid valves A, B, and C, while receiving input signals from various sensors and switches located throughout the vehicle. The shift solenoid valves shift the positions of the shift valves to switch the port leading hydraulic pressure to the clutch. The A/T clutch pressure control solenoid valves A, B, and C regulate their respective pressure, and pressurize to the clutches to engage it and its corresponding gear. The pressures of the A/T clutch pressure control solenoid valves also apply to the shift valves to switch the port.

Lock-up Mechanism

The lock-up mechanism operates in [D] position (3rd and 4th) and [D] position over-drive off mode (3rd). The pressurized fluid is drained from the back of the torque converter through a fluid passage, causing the torque converter clutch piston to be held against the torque converter cover. As this takes place, the mainshaft rotates at the same speed as the engine crankshaft. Together with the hydraulic control, the PCM optimizes the timing and volume of the lock-up mechanism. When the shift solenoid valve E is turned on by the PCM, shift solenoid valve E pressure switch the lock-up shift valve lock-up on and off. The A/T clutch pressure control solenoid valve A and the lock-up control valve control the volume of the lock-up conditions.

Gear Selection

The shift lever has six positions: [P] PARK, [R] REVERSE, [N] NEUTRAL, [D] DRIVE 1st through 4th gear range with Over-drive mode, and 1st through 3rd gear range with Over-drive OFF mode, [2] 2nd gear, and [1] 1st gear.

Position Description 
[P] PARK Front wheels locked; park pawl engaged with park gear on countershaft. All clutches are released. 
[R] REVERSE Reverse; reverse selector engaged with countershaft reverse gear and 4th clutch engaged. 
[N] NEUTRAL All clutches are released. 
[D] DRIVE
with Over-drive mode
(1st through 4th) 
General driving; starts off in 1st, shifts automatically to 2nd, 3rd, then 4th, depending on vehicle speed and throttle position. Downshifts through 3rd, 2nd, and 1st on deceleration to stop. The lock-up mechanism operates in 3rd and 4th gears. 
[D] DRIVE
with Over-drive OFF mode
(1st through 3rd) 
For rapid acceleration at highway speeds and general driving, up-hill and down-hill driving; starts off in 1st, shifts automatically to 2nd, then 3rd, depending on vehicle speed and throttle position. Downshifts through 2nd to 1st on deceleration to stop. The lock-up mechanism operates in 3rd gear. 
[2] SECOND Used for engine braking or better traction starting off on loose or slippery surfaces; stays in 2nd gear, does not shift up and down. 
[1] FIRST Used for engine braking; stays in 1st gear, does not shift up. 

Starting is possible only in [P] and [N] positions because of a slide-type neutral-safety switch.

Automatic Transaxle (A/T) Gear Position Indicator

The A/T gear position indicator in the instrument panel shows which position has been selected.

Transfer Mechanism (4WD)

The transfer mechanism consists of the transfer drive gear on the differential, the transfer shaft, the transfer drive gear (hypoid gear), the transfer driven gear shaft (hypoid gear), and the companion flange. The transfer mechanism assembly is on the rear of the transmission, beside the differential. The transfer drive gear on the differential drives the transfer gear shaft and transfer driven gear (hypoid gear), and the transfer drive gear (hypoid gear) drives the transfer driven gear shaft (hypoid gear). Power is transmitted from the transfer drive gear on the differential to the rear differential via the transfer and the propeller shaft.