AS68RC Automatic Transmission - Service Information: Overview RAM Pickup 2500

DESCRIPTION

Scheme 584

The AS68RC six speed automatic transmission displays durability characteristics required in the truck and bus industries, while serving fundamental roles in improving vehicle performance through a new gear train and a multi disc lock up clutch. Other features include better braking performance, higher torque capacity with less weight , smoother shift quality while attaining high reliability.

The hydraulic control mechanism utilizes direct control of main pressure by use of a linear solenoid.

The primary mechanical components of the transmission consist of the following

1. Three sets of clutch packs
2. Two sets of brake packs
3. A one way clutch
4. Three planetary gear sets
5. Single stage, three element, two phase type torque converter.
6. Valve body
7. Linear solenoids
8. Shift solenoids
9. Oil Pump

The Transmission Control Module (TCM) is the "heart" or "brain" of the electronic control system and relies on information from various direct and indirect inputs (sensors, switches, etc.) to determine driver demand and vehicle operating conditions. Depending on the vehicle configuration, the TCM may be a standalone module or it may be housed along with the Powertrain Control Module (PCM) in a single module. With this information, the TCM can calculate and perform timely and quality shifts through various output or control devices.

Scheme 585

Note. Some transmissions may have the ID. Tag located on the either side of the transmission case.

Transmission identification numbers are located on top of the torque converter housing. Refer to this information when ordering replacement parts. The label gives additional information which may also be necessary for identification purposes.

OPERATION

The AS68RC offers full electronic control of all automatic up and downshifts, and features real-time adaptive closed-loop shift and pressure control. Electronic shift and torque converter clutch controls help protect the transmission from damage due to high temperatures, which can occur under severe operating conditions. By altering shift schedules, line pressure, and converter clutch control, these controls reduce heat generation and increase transmission cooling.

Wide gear range and close ratio was implemented in order to improve both operational and fuel performance. The first gear ratio was lowered by 18% with respect to conventional four speed automatics to improve launch capabilities.

The hydraulic control system design (without electronic assist) provides the transmission with REVERSE, FIFTH and THIRD. This design allows the vehicle to be driven (in "limp-in" mode) in the event of a electronic control system failure, or a situation that the Transmission Control Module (TCM) recognizes as potentially damaging to the transmission.

The TCM also performs certain self-diagnostic functions and provides comprehensive information (sensor data, DTC's, etc.) which is helpful in proper diagnosis and repair. Additionally, the ability to calibrate the TCM with the StarScan R allows for the transmission to deliver optimum shift quality to customers with diverse vehicle applications.

Scheme 586

Scheme 587

OPERATION AND TIMING OF CLUTCHES , BRAKES AND SOLENOIDS

Scheme 588

Scheme 589

FIRST GEAR

When oil pressure is applied to K1 clutch (2) and the input shaft (1) and sun gear shaft (12) which are directly connected; as a result of the clockwise turning effect of the input shaft (1), the sun gear shaft (12) rotates clockwise.

The rotation of the sun gear shaft (12) is transmitted as counterclockwise turning effect to the P3 planetary pinion gear as it attempts to rotate the P3 planetary annulus gear counterclockwise.

The counterclockwise rotation is checked by the action of the F1 one-way clutch (6), the P3 planetary pinion gear rotates clockwise (revolves centering on the sun gear shaft (12), while rotating clockwise on its own axis.

This conveys a clockwise turning effect to the P3 planetary annulus (9) and the output shaft (8) connected to it.

Scheme 590

SECOND GEAR

When oil pressure is applied to K1 clutch (2) and the input shaft (1) and the sun gear shaft (12) which are directly connected ; the sun gear shaft (12) rotates clockwise.

The clockwise rotation of the sun gear shaft (12) is transmitted as counterclockwise turning effect to the P2 planetary pinion gear and attempts to rotate the P2 planetary annulus gear counterclockwise.

Since the P2 planetary annulus gear is fixed by the B1 brake (5), the P2 planetary pinion gear rotates counterclockwise, and the clockwise turning effect is conveyed to the P2 planetary annulus (10).

As a result, a clockwise turning effect is given to the P3 planetary annulus gear that is connected to the P2 planetary annulus (10).

The clockwise turning effect of the sun gear shaft (12) is also conveyed to the P3 planetary pinion gear, the P3 planetary annulus gear is also decelerated and is rotating clockwise.

The P3 planetary pinion gear revolves clockwise while rotating counterclockwise on its own axis, and the clockwise turning effect is conveyed to the output shaft (8) that is connected to the P3 planetary annulus (9).

Scheme 591

THIRD GEAR

When oil pressure is applied to the K3 clutch (4), the clockwise turning effect of the P1 planetary annulus gear is conveyed and the P2 planetary annulus gear rotates clockwise.

When oil pressure is applied to the K1 clutch (2), the input shaft (1) and the sun gear shaft (12) are directly connected, the sun gear shaft (12) rotates clockwise.

As a result, the P2 planetary pinion gear revolves clockwise while rotating clockwise on its own axis, thus a clockwise turning effect is given to the P3 planetary annulus gear that is connected to the P2 planetary annulus (10).

This rotation and clockwise turning effect of the sun gear shaft (12) gives turning effect to the P3 planetary pinion gear to revolve clockwise while rotating clockwise on its own axis, and a clockwise turning effect then given to the P3 planetary annulus (9) and also to the output shaft (8).

Scheme 592

FOURTH GEAR

When oil pressure is applied to K1 clutch (2), and the input shaft (1) and the sun gear shaft (12) are directly connected, the sun gear shaft (12) rotates clockwise.

When oil pressure is applied to K2 clutch, then the P3 planetary gear rotates clockwise via the P2 planetary gear (10).

This action gives a clockwise turning effect to the P3 planetary annulus (9) and the clockwise turning effect is given to the output shaft (8).

Scheme 593

FIFTH GEAR

When oil pressure is applied to the K3 clutch (4), a clockwise turning effect of the P1 planetary annulus gear is transmitted and the P2 planetary annulus gear rotates clockwise.

When oil pressure is applied to the K2 clutch (3), a clockwise turning effect is given to the P2 planetary annulus (10).

As the P2 planetary annulus gear rotates, the clockwise turning effect of the sun gear shaft (12) is obtained.

Then, a clockwise turning effect of the P3 planetary annulus gear that is connected to the P2 planetary annulus (10) and a clockwise turning effect of the sun gear shaft gives a clockwise turning effect to the P3 planetary annulus (9), and a clockwise turning effect is also given to the output shaft (8).

Scheme 594

SIXTH GEAR

Oil pressure is applied to the K2 clutch (3), and a clockwise turning effect is given to the P2 planetary annulus (10).

Oil pressure is applied to the B1 brake, and since the P2 planetary annulus gear is fixed, the P2 planetary pinion gear rotates counterclockwise on it's own axis while revolving clockwise.

As a result, the sun gear shaft (12) obtains a clockwise turning effect.

The clockwise turning effect of the sun gear shaft (12) and the P3 planetary annulus gear connected to the P2 planetary annulus (10) gives a clockwise turning effect to the P3 planetary annulus, and the clockwise turning effect is then also given to the output shaft.

Scheme 595

REVERSE GEAR

When oil pressure is applied to the K3 clutch (4) and a clockwise turning effect of the P1 planetary annulus gear is transmitted; the P2 planetary annulus gear rotates clockwise.

Oil pressure is then applied to the B2 brake to fix the P3 planetary annulus gear and P2 planetary annulus (10) that is connected to it.

As a result the P2 planetary pinion gear rotates clockwise with it's position fixed giving a counterclockwise turning effect to the sun gear shaft (12).

As a result of the clockwise turning effect given to the sun gear shaft (12) , and the fixed P3 planetary annulus gear , the P3 planetary pinion gear revolves counterclockwise while rotating clockwise on it's own axis, and the counterclockwise turning effect is then given to the P3 planetary annulus (9) and also to the output shaft (8).

Note. Before attempting any repair on a automatic transmission, check for Diagnostic Trouble Codes with the scan tool.

Transmission malfunctions may be caused by these general conditions

1. Poor engine performance
2. Improper adjustments
3. Hydraulic malfunctions
4. Mechanical malfunctions
5. Electronic malfunctions

Diagnosis of these problems should always begin by checking the easily accessible variables: fluid level and condition, gearshift cable adjustment. Then perform a road test to determine if the problem has been corrected or if more diagnosis is necessary. If the problem persists after the preliminary tests and corrections are completed, hydraulic pressure checks should be performed.

The function of a one-way mechanical clutch is that it allows the clutch to freewheel in one direction during certain operating conditions of the transmission.

The F1 one way clutch locks the front planetary carrier and rear planetary ring gear against counterclockwise rotation, only allowing them to rotate clockwise.

Scheme 596

1. Remove the snap ring (1 from the F1 one way clutch assembly.
2. Remove the F1 one way clutch (2) from the F1 one way clutch outer race (3)

Note. The 68RFE transmission does not use a number 7 thrust bearing.

Scheme 597

GEAR SETS

Scheme 598

The P1 planetary gear set is in front of the transmission case bulkhead located behind the oil pump, C1 and C2 clutch assemblies and is bolted to the transmission case. The P1 planetary gear set works in conjunction with the C3 clutch assembly.

Scheme 599

The P2 planetary gear set is first gear set located behind the transmission case bulkhead. The P2 planetary gear set works in conjunction with the B1 brake clutch.

Scheme 600

The P3 planetary gear set is located behind the P2 planetary gear set in front of the F1 one-way clutch. The P3 planetary gear set works in conjunction with the B2 brake clutch.

Planetary gear sets are so named because of their physical arrangement. All planetary gear sets contain at least three main components.

1. A sun gear at the center of the gear set.
2. A carrier assembly with planetary pinion gears that rotate around the sun gear.
3. An internal annulus that encompasses the entire gear set.

This arrangement provides both strength and efficiency and also evenly distributes the energy forces flowing through the gear set. Another benefit of planetary gears is that gear clash, a common occurrence in manual transmissions, is eliminated because the gear teeth are always in mesh.

The system locks the shifter into the PARK position. The interlock system is engaged whenever the ignition switch is in the LOCK or ACCESSORY position. An additional electrically activated feature will prevent shifting out of the PARK position unless the brake pedal is depressed approximately one-half an inch. A magnetic holding device in line with the park lock cable is energized when the ignition is in the RUN position. When the key is in the RUN position and the brake pedal is depressed, the shifter is unlocked and will move into any position. The interlock system also prevents the ignition switch from being turned to the LOCK or ACCESSORY position, unless the shifter is fully locked into the PARK position.

As the torque converter rotates, the converter hub rotates the oil pump drive gear. As the drive gear rotates both driven gears, a vacuum is created when the gear teeth come out of mesh. This suction draws fluid through the pump inlet from the oil pan. As the gear teeth come back into mesh, pressurized fluid is forced into the pump outlet and to the oil pump valves.

Scheme 601

The Primary Regulator Valve (1) controls line pressure fed to the elements.

The Secondary Regulator Valve (2) controls pressure fed from the Primary Regulator Valve to the torque converter, and controls lubrication pressure for various parts.

The relay is supplied fused B+ voltage, energized by the TIPM, and is used to supply power to the TCM when the transmission is in normal operating mode.

The TIPM energizes the transmission control relay. When the relay is "off", no power is supplied to the TCM and the transmission will not operate.

The Input and Output Speed Sensors are two-wire magnetic pickup devices that generate DC square wave signals as rotation occurs. They are mounted in the left side of the transmission case and are considered primary inputs to the Transmission Control Module (TCM).

The Input Speed Sensor provides information on how fast the input shaft is rotating. As the "teeth" of the gear pass by the sensor coil, an DC square wave is generated and sent to the TCM. The TCM interprets this information as input shaft RPM.

The Output Speed Sensor generates an DC signal in a similar fashion, though its coil is excited by rotation of the rear planetary carrier lugs. The TCM interprets this information as output shaft RPM.

The TCM compares the input and output speed signals to determine the following

1. Transmission gear ratio
2. Speed ratio error detection
3. CVI calculation

The TCM also compares the input speed signal and the engine speed signal to determine the following

1. Torque converter clutch slippage
2. Torque converter element speed ratio

The transmission range sensor prohibits the vehicle from starting in any gear other than park and neutral.

The gear shift mechanism provides four shift positions which are

1. Park (P)
2. Reverse (R)
3. Neutral (N)
4. Drive (D)

DRIVE range provides FIRST, SECOND, THIRD, FOURTH, OVERDRIVE FIFTH, OVERDRIVE SIXTH gear ranges. The shift into OVERDRIVE FOURTH and FIFTH gear ranges occurs only after the transmission has completed the shift into D THIRD gear range.

The SIXTH gear upshifts occur automatically unless the Tow/Haul or OD Off mode is enabled. No upshift to FIFTH or SIXTH gears will occur if any of the following are true

1. The transmission fluid temperature is below 5° C (41° F).
2. The shift to Fourth is not yet complete.
3. Vehicle speed is too low for the 4-5 or 5-6 shifts to occur.
4. Transfer case is in low range.

Upshifts into FOURTH or FIFTH will be delayed when the transmission fluid temperature is below 4.5° C (40° F) or above 115.5° C (240° F).

The tow/haul overdrive OFF (control) switch is located in the instrument panel switch pod. The switch is a momentary contact device that signals the PCM to toggle current status of the overdrive function. Refer to POD, Switch , Description .

At key-on, overdrive operation is allowed. Pressing the switch once enables Tow/Haul mode and the Tow/Haul lamp will be illuminated. In Tow/Haul mode, 6th gear is disabled and 4-5 upshifts are delayed. Shifts into 5th gear are still allowed under steady cruise conditions. Closed throttle downshifts (for improved engine braking) may occur during steady braking maneuvers. Pressing the switch a second time enables OD Off mode, where all 5th and 6th gear operation is inhibited. Pressing the switch a third time restores normal operation. Normal operation is always the default at start-up; the switch must be pressed after each key start if Tow/Haul mode is desired.

The torque converter is a hydraulic device that couples the engine crankshaft to the transmission. The torque converter consists of an outer shell with an lock-up damper (1), lock-up piston (3), pump impeller (4), turbine runner (5), stator (6), and one-way clutch (7). The converter clutch provides reduced engine speed and greater fuel economy when engaged. Clutch engagement also provides reduced transmission fluid temperatures.

The torque converter is a sealed, welded unit that is not repairable and is serviced as an assembly.

Scheme 602

The impeller is an integral part of the converter housing. see scheme 288 The impeller consists of curved blades placed radially along the inside of the housing on the transmission side of the converter. As the converter housing is rotated by the engine, so is the impeller, because they are one and the same and are the driving members of the system.

Scheme 603

The turbine is the output, or driven, member of the converter. see scheme 289 The turbine is mounted within the housing opposite the impeller, but is not attached to the housing. The input shaft is inserted through the center of the impeller and splined into the turbine. The design of the turbine is similar to the impeller, except the blades of the turbine are curved in the opposite direction.

Scheme 604

The stator assembly is mounted on a stationary shaft which is an integral part of the oil pump. see scheme 290 The stator (1) is located between the impeller (2) and the turbine (4) within the torque converter case.

The stator contains an one-way clutch (1-4), which allows the stator to rotate only in a clockwise direction. When the stator is locked against the over-running clutch, the torque multiplication feature of the torque converter is operational.

The torque converter transmits engine torque to the transmission. When it is not locked up, it transmits the torque by means of oil. When it is locked up, it transmits the torque by means of the lockup piston.

The lockup damper is designed to soften the impact as the torque converter locks up.

The torque converter is a 3-element, single-stage, 2-phase type.

The term "single-stage" indicates that there is 1 turbine runner (output element). The term "2-phase" indicates that the mechanism works as a torque converter when the turbine runner is turning slowly relative to the pump impeller and as a fluid coupling when the turbine runner is turning quickly relative to the pump impeller.

Scheme 605

The torque converter activation pressure is not supplied between the converter front cover and lockup piston via passage (3). The lockup clutch (1) and the plate (2) are therefore disengaged and the lockup function is inactive.

Scheme 606

The torque converter activation pressure is supplied between the converter front cover and lockup piston via passage (3). The lockup clutch (1) and the plate (2) are therefore engaged and the lockup function is active.

The valve body consists of a two piece aluminum valve body. Extensive electronic control effected by a microcomputer (the automatic transmission electronic control unit) over the hydraulic circuitry enables precise control over gearshifts. The valve body contains valves and pressure sensors that control fluid delivery to the torque converter clutch, forward clutches, and brake clutches.

Scheme 607

The upper valve body contains the following components

1. 1 = Combined Drain
2. 2 = Gain change solenoid valve
3. 3 = Manual valve
4. 4 = Modulator valve
5. 5 = Shift solenoid valve No. 3
6. 6 = Shift solenoid valve No. 2
7. 7 = Shift valve No. 1

Scheme 608

The lower valve body contains the following components

1. 1 = Control valve No. 3
2. 2 = Shift solenoid valve No. 4
3. 3 = Lockup control valve
4. 4 = Control valve No. 1
5. 5 = Control valve No. 2

Scheme 609

There are eight pressure switches and one ATF temperature switch used to inform the Transmission Control Module (TCM) when there is pressure in various hydraulic circuits. Six of them are located on the bottom of the valve body. The remainder are located on the top of the valve body.

Scheme 610

Eight solenoids are used to control various shift functions in the transmission. Four are located on the top of the valve body (3, 4) and the remainder are located on the bottom of the valve body.