Automatic Transmission/Transaxle: Description and Operation
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GENERAL INFORMATION
The identification markings and usage of the TorqueFlite Transmissions is charted in Diagnosis and Tests.
Because of the similarity in design and in servicing the transmissions, the procedures have been combined in this Manual. Where variations in procedures occur, application is indicated (Fig. 1, 2 or 3). Transmission operation requirements are different for each vehicle and engine combination and some internal parts will be different to provide for this. Therefore, when replacing parts, refer to the seven digit part number stamped on left side of the transmission oil pan flange.
ALL A-904 and A-904-LA transmissions are equipped with a 'wide ratio' gearset. Low gear ratio is 2.74 to 1. The sun gear and front planetary gearset is unique to the 'wide ratio' transmission. The rear planetary gearset remains the same as previous models.
The transmission combines a torque converter and a fully-automatic 3-speed gear system. The converter housing and transmission case are an integral aluminum casting. The transmission consists of two multiple disc clutches, an overrunning clutch, two servos and bands, and two planetary gear sets to provide three forward ratios and a reverse ratio. The common sun gear of the planetary gear sets is connected to the front clutch by a driving shell which is splined to the sun gear and to the front clutch retainer. The hydraulic system consists of an oil pump, and a single valve body which contains all of the valves except the governor valve.
Venting of the transmission is accomplished by a passage through the upper part of the oil pump housing.
The torque converter is attached to the crankshaft through a flexible driving plate. Cooling of the converter is accomplished by circulating the transmission fluid through an oil-to-water type cooler, located in the radiator lower tank. The torque converter assembly is a sealed unit which cannot be disassembled. A lock-up clutch is located inside most torque converters.
The transmission fluid is filtered by an internal "Dacron Type" filter attached to the lower side of the valve body assembly.
Engine torque is transmitted to the torque converter, then, through the input shaft to the multiple disc clutches in the transmission. The power flow depends on the application of the clutches and bands. Refer to "Elements in use chart" in Diagnosis and Test section. "Elements in Use Chart" in Diagnosis and Tests section.
lock-up Torque Converter
The lock-up torque converter is Standard on all vehicles except 225 CID. engines.
The lock-up mode is activated only in direct drive and above a minimum preset vehicle speed. At wider throttle openings, where the 2-3 upshift occurs above the minimum lock-up speed, the lock-up shift will occur immediately after the 2-3 upshift.
Lock-up and non lock-up torque converters and transmissions are not intermixable.
HYDRAULIC CONTROL SYSTEM
The hydraulic control circuits show the position of the various valves with color coded passages to indicate those under hydraulic pressure for all operations of the transmission. Diagrams
The hydraulic control system makes the transmission fully automatic, and has four important functions to perform. In a general way, the components of any automatic transmission control system may be grouped into the following basic groups:
The pressure supply system, the pressure regulating valves, the flow control valves, the clutches, and band servos.
Taking each of these basic groups or systems in turn, the control system may be described as follows:
Pressure Supply System
The pressure supply system consists of an oil pump driven by the engine through the torque converter. The single front pump furnishes pressure for all the hydraulic and lubrication requirements.
Pressure Regulating Valves
The pressure regulating valves consist of a regulator valve which controls line pressure at a value dependent 0n throttle opening. The governor valve transmits regulated pressure to the transmission (in conjunction with vehicle speed) to control upshift, downshift, and lock-up speeds.
The throttle valve transmits regulated pressure to the transmission (in conjunction with throttle position) to control upshift, downshift, and lock-up speeds.
Flow Control Valves
The manual valve provides the different transmission drive ranges as selected by the vehicle operator.
The 1-2 shift valve automatically shifts the transmission from low to second or from second to low depending on the vehicle operation.
The 2-3 shift valve automatically shifts the transmission from second to direct or from direct to second depending on the vehicle operation.
The kickdown valve makes possible a forced downshift from direct to second, second to breakaway, or direct to breakaway (depending on vehicle speed) by depressing the accelerator pedal past the detent "feel" near wide open throttle. The throttle pressure plug at the end of the 2-3 shift valve, provides a 3-2 downshift with varying throttle openings depending upon vehicle speed.
The 1-2 shift control valve transmits 1-2 shift control pressure to the transmission accumulator piston to control the kickdown band capacity on 1-2 upshifts and 3-2 downshifts. The limit valve determines the maximum speed at which a 3-2 part throttle kickdown can be made. Some transmissions do not have the Limit Valve and the maximum speed for the 3-2 kickdown is at the "detent" position.
The shuttle valve has two separate functions and performs each independently of the other. The first is that of providing fast release of the kickdown band, and smooth front clutch engagement when the driver makes a "lift-foot" upshift from second to direct. The second function of the shuttle valve is to regulate the application of the kickdown servo and band when making direct to second kickdowns.
The lock-up valve automatically applies the torque converter lock-up clutch if vehicle is above a predetermined speed in direct gear.
The fail-safe valve restricts feed to the lock-up clutch if front clutch pressure drops. It permits lockup only in direct gear and provides a fast lock-up release during a kickdown.
The switch valve directs oil to apply the lock-up clutch in one position and releases it in the other as well as directs oil to the cooling and lube circuits. The switch valve also regulates the oil pressure to the torque converter and limits the maximum oil pressure to 130 psi.
Clutches, Band Servos, and Accumulator
The front and rear clutch pistons, and both servo pistons are moved hydraulically to engage the clutches and apply the bands. The pistons are released by spring tension when hydraulic pressure is released. On the 2-3 upshift, the kickdown servo piston is released by spring tension and hydraulic pressure and the lock-up piston is applied by hydraulic pressure within the torque converter above a predetermined vehicle speed in direct gear.
The accumulator controls the hydraulic pressure on the apply side of the kickdown servo during the 1-2 shift; thereby, cushioning the kickdown band application at any throttle position.
OPERATING INSTRUCTIONS
The transmission will automatically upshift and downshift at approximately the speeds shown in the "Automatic Shift Speed Chart." All shift speeds given in the "Chart" may vary somewhat due to production tolerances and rear axle ratios. The quality of the shifts is very important. All shifts should be smooth and positive with no noticeable engine runaway. See "Diagnosis and Tests" for chart. Initial Inspection and Diagnostic Overview
Gearshift and Parking Lock Controls
The transmission is controlled by a "lever type" gearshift incorporated within the steering column. The control has six selector lever positions: "P" (park), "R" (reverse), "N" (neutral), and "D" (drive), "2" (second) and "1" (first). Some vehicles are equipped with a "lever type" console gearshift which has the same selector lever positions. The parking lock is applied by moving the selector lever past a gate to the "P" position. Do not apply the parking lock until the vehicle has stopped; otherwise, a severe ratcheting noise will occur.
Starting the Engine
The engine will start with the selector lever III either the "P" (park) or "N" (neutral) positions. As a safety precaution when starting in the "N" (neutral position, apply the parking or foot brake. The TorqueFlite transmission will not permit starting the engine by pushing or towing.
Mountain Driving
When driving in the mountains with either heavy loads or when pulling trailers, the "2" (second) or "1" be towed safely in "N" (neutral) with rear wheels on require heavy throttle for 1/2 mile or more. This reduces possibility of overheating the transmission and converter under these conditions.
Towing Vehicle
Transmission Inoperative: Tow the vehicle with a rear end pickup or remove the propeller shaft. Transmission Operating Properly: The vehicle may be towed safely in N (neutral) with rear wheels on the ground at a speed not to exceed 30 mph. If the vehicle is to be towed for extended distances, it should be done with a rear end pickup or the propeller shaft removed. Because the transmission receives lubrication only when the engine is running, it is good practice to always tow a disabled vehicle with a rear end pickup or remove the propeller shaft.
LUBRICATION
Inspect fluid level on dipstick every six months with engine idling and transmission in neutral position and vehicle on level ground. A properly filled transmission will read near the "add" mark when fluid temperature is 70 degree fahrenheit (21 degrees Celsius) and near (but not over) the "full" mark at 180 degrees fahrenheit 82 degrees Celsius) (average operating temperature).
Fluid and filter Changes
Fluid and filter changes or band adjustments are not required for average passenger car usage. Severe usage as defined below, requires that fluid and filter be changed and bands adjusted every 15,000 miles (24 000 kilometers).
(1) More than 50% operation in heavy city traffic during hot weather (above 90�F.) (32�C.).
(2) Police, Taxi, Limousine, Commercial Type Operation, and Trailer Tow.
NOTES:
(1) When the factory fill fluid is changed as recommended above, only fluids of the type labeled DEXRON II" Automatic Transmission Fluid should be used. A band adjustment and filter change should be made at the time of the oil change.
(2) If the transmission is disassembled for any reason, the fluid and filter should be changed, and the bands adjusted.
Drain and Refill
(1) Raise vehicle on a hoist. Place a drain container with a large opening, under transmission oil pan.
(2) Loosen pan bolts and tap the pan at one corner to break it loose allowing fluid to drain, then remove the oil pan.
(3) If necessary, adjust the reverse band.
(4) Install a new filter on bottom of the valve body, and tighten retaining screws to 35 in.lbs. (4 N.m).
(5) Clean the oil pan, make sure the round magnet is located over the boss in the front, right hand corner of the oil pan. Install oil pan using a new gasket. Tighten oil pan bolts to 150 in. lbs. (17 N.m).
(6) Pour four quarts of "DEXRON II" type Automatic Transmission Fluid through the filler tube.
(7) Start engine and allow to idle for at least two minutes. Then, with parking brake on, move selector lever momentarily to each position, ending in the neutral position.
(8) Add sufficient fluid to bring level to the "ADD" mark. Recheck fluid level after transmission is at normal operating temperature. The level should be between the "FULL" mark and "ADD" mark with vehicle on level ground. To prevent dirt from entering transmission, make certain that dipstick cap is fully seated onto the filler tube.