Chapter 3
General Theories of Operation Diagnosis, Maintenance, and Basic Adjustments
Upon completion and review of this chapter, the student should be able to:
Classroom Manual Objectives· List the factors that determine when an automatic transmission will automatically shift.
· Describe the four basic systems of all automatic transmissions.
· Describe the operation and purpose of a torque converter.
· Explain Pascal’s Law and how it applies to the operation of an automatic transmission.
· Explain the basic operation of hydraulic machines.
· Identify the major components in a transmission’s hydraulic circuit and describe how they provide fluid flow and pressurization.
· List the various types of reaction members commonly used in automatic transmissions.
· Describe the purpose of a transmission’s valve body.
· List and describe the various load-sensing devices used in an automatic transmission's hydraulic system.
· Describe the basic construction of automatic transmission housings, including the purpose of the various mechanical and electrical connections. / Shop Manual Objectives
· Listen to the driver’s complaint, road test the vehicle, and then determine the needed repairs.
· Diagnose unusual fluid usage, level, and condition problems.
· Replace automatic transmission fluid and filters.
· Diagnose noise and vibration problems.
· Diagnose electronic, mechanical, and vacuum control systems.
· Inspect, replace, and align power train mounts.
· Inspect, adjust, and replace vacuum modulator, lines, and hoses.
· Diagnose mechanical and vacuum control systems; determine needed repairs.
· Perform oil pressure tests; determine needed repair.
· Inspect, adjust, and replace manual valve shift linkage.
· Inspect, adjust, and replace cables or linkages for throttle valve (TV) kickdown and accelerator pedal.
· Inspect and replace external seals and gaskets while the transmission is in the vehicle.
· Inspect, repair, and replace extension housing.
· Inspect and replace speedometer drive gear, driven gear, and retainers while the transmission is in the vehicle.
· Inspect and replace parking pawl, shaft, spring, and retainer while the transmission is in the vehicle.
· Adjust bands.
Overview
This chapter in both manuals covers the general theory of operation of an automatic transmission, discussing all the basic parts. The chapters also cover the method of identification, diagnostic procedures, and identification of the cause of oil leaks. They cover basic service and repair procedures.
Reading Assignments
Classroom Manual, pages 45-79
Shop Manual, pages 71-112
Terms to Know
AccumulatorAeration
Belleville spring
Check ball valves
Dynamic pressure
Engine vacuum
Flow chart
Flow-directing valves
Gear-type pump
Governor
Impeller
Input shaft
Kickdown
Kickdown switch
Manual shift valve
MAP sensor / Mechanical advantage
MLP
Modulator valve
Neutral safety switch
Orifice
Output shaft
Oxidation
Poppet valves
Pressure-regulating valves
Reaction members
Reverse stall test
Rotor-type pump
Separator plate
Servo
Shift feel / Static pressure
Stator
TV linkage
Throttle valve
Torque converter
Torque converter cover
Transaxle Identification Number
Transfer plate
Turbine
Vacuum modulator
Vane-type pump
Vehicle speed sensor
VFM
Work
Lecture Outline and Notes
I. Objectives
Review the chapter’s objectives.
II. Introduction
Discuss the many uses of the automatic transmission and transaxle.
III. Basic Operation [Job Sheet 3]
A. Describe the operation of the torque converter.
B. Discuss the planetary gears and their operation.
C. Briefly describe the hydraulic function and the valve body.
D. Describe the electronic controls used in the late models.
E. Briefly describe the Autostick transmission system.
IV. Identification
Discuss how to identify a transmission or transaxle.
V. Diagnostics
A. Customer’s Complaint
1. Question the customer to determine what, how, when, and where the
failure occurs.
2. Test-drive the vehicle with the customer when possible.
3. Ensure your terminology and the customer’s are the same.
B. Fluid Checks
1. Explain the purpose of checking fluids for condition and level.
2. Identify the type of fluid that should be used.
VI. Fluid Leaks
Discuss in general the method for checking for fluid leaks.
A. Oil Pan
Discuss how to find and service an oil pan leak.
B. Torque Converter
Discuss where a torque converter leak might show up on both rear-wheel and front-wheel drive vehicles.
C. Cooler and Line Inspection
Discuss inspection techniques for the transmission cooler and cooler lines/hoses.
D. Extension Housing
Describe the procedure for checking for a loose or worn bushing and seal.
E. Rear Oil Seal and Bushing Replacement
Describe the procedure for the replacement of oil seals and bushings.
F. Speedometer Drive
Discuss how the seal or seals for speedometer connections and speed sensors are normally replaced.
VII. Road Testing the Vehicle
A. Describe the method of road checking the transmission for problems.
B. Describe the type of noises that might come from the transmission.
C. Describe the operation of a vacuum modulator. Describe some shift problems related directly to the modulator.
VIII. Planetary Gearing
A. Description
1. Describe gear members.
2. Describe the interaction between the members.
B. Compound Planetary Gearsets
1. Describe a compound gearset.
2. Explain the increased number of gear ratios available.
IX. Transmission Controls
Describe how and why the transmission shifts gears according to the inputs it receives.
X. Laws of Hydraulics
A. Discuss Pascal’s Law for hydraulics.
B. Discuss using fluid to transfer power and to lubricate.
C. Describe the mechanical advantage of hydraulics.
D. Discuss using hydraulics to achieve mechanical advantage.
E. Describe the use of fluid in the transmission.
F. Discuss the use of hydraulics to apply servos and clutches.
XI. Application of Hydraulics in Transmissions
A. ATF
1. Discuss the cooling, lubrication, and cleaning functions of ATF.
2. Explain how ATF is used to shift gears and control valve movement.
3. Describe how ATF is used to operate apply devices.
B. Reaction Members
Discuss the reaction members of a transmission.
C. Valve Body
1. Discuss the construction of a valve body.
2. Discuss the purpose of the valves.
D. Oil Flow
Discuss the oil flow and how it is directed.
E. Pressure Regulator Valve
1. Discuss the valve’s operation.
2. Explain the action of this valve in a transmission.
XII. Pressure Boosts
A. Pressure Boosts
1. Describe the pressure boost.
2. Explain why it is needed in transmissions.
B. Governor Assembly
Describe the operation and purpose.
C. Kickdown Valve
1. Describe the kickdown function.
2. Explain why it is needed in automatic transmissions.
D. Shift Feel
Explain the driver’s desire to feel shifts.
XIII. Pressure Tests
Demonstrate how a pressure test is conducted and show where the pressure taps are located on several different transmissions.
A. Discuss the need for a pressure test.
B. Describe pressure testing procedures.
C. Discuss the development of a chart to track and diagnose transmission
operations.
XIV. Diagnose Hydraulic and Vacuum Control Systems
Talk the students through a normal pressure chart and explain what is indicated by abnormal, low, and high readings; include a discussion on how faulty electrical, mechanical, and vacuum controls will affect the pressure readings.
A. Discuss the testing of the controls of the automatic transmission.
B. Describe modulator vacuum testing.
C. Discuss modulator adjustment procedures.
D. Discuss air pressure testing.
XV. Linkages
Discuss the different linkages used in transmission mounts.
A. Neutral Safety Switch
1. Describe the switch’s operation and purpose.
2. Explain adjusting procedures.
B. Gear Selection Linkage
1. Discuss manual gear selection.
2. Discuss adjustment of the gear selection linkage.
C. Throttle Valve Linkages
1. Describe problems that may be caused by an out of adjustment linkage.
2. Discuss adjustment procedures.
D. Kickdown Switch Adjustment
1. Explain the purpose of the switch.
2. Discuss testing and adjusting the switch.
XVI. Other Adjustments
Discuss the other items on a transmission that may need to be adjusted, such as early vacuum modulators and bands. Also discuss the procedure for adjusting bands when there is an external band adjuster on the transmission.
XVII. Transmission/Transaxle Housings
Discuss the housings and the mechanical connections to the housing for both rear and front wheel drives.
XVIII. Mounts
A. Checking Transaxle Mounts
1. Discuss the mounts used to support the transmission on a RWD
vehicle.
2. Describe the mounts used to support the FWD power train.
3. Describe the method for checking transmission and engine mounts.
XIX. Transmission Cooler and Line Inspection
A. Discuss the importance of the fluid cooler.
B. Demonstrate how to conduct a thorough inspection of the radiator,
cooler, and cooler lines.
C. Discuss service on transmission oil cooler lines and coolers.
D. Explain the type of defects that may be found during inspection.
XX. Summary
Review the material covered, emphasizing the main points and key words.
Chapter 3 Answers to Review Questions
CLASSROOM MANUAL, PAGES 79-81
Short Answer Essays
1. “Shift feel” is controlled by the pressure at which each reaction member is applied or released, the rate at which each is pressurized or exhausted, and the relative timing of the apply and release of the members.
2. A typical automatic transmission consists of four basic systems: the torque converter, planetary gearsets, hydraulic system, and reaction members.
3. A vacuum modulator measures engine vacuum to sense the load placed on the engine and the drive train. A vacuum modulator is a load sensing device that increases or decreases fluid pressure in response to a vacuum signal that varies with throttle opening and vehicle load.
4. Shift timing is determined by throttle pressure and governor pressure acting on opposite ends of the shift valve. Shift valves control the upshifting and downshifting of the transmission by controlling the flow of pressurized fluid to the apply devices that engage the different gears.
5. As engine load increases, engine vacuum decreases.
6. Transmissions are equipped with a fluid cooler that prevents the overheating of the fluid, which could result in damage to the transmission.
7. When the engine is operating under heavy load conditions, fluid pressure is raised to increase the holding capacity of a reaction member, and upshifts are delayed.
8. The torque converter engages and disengages the engine’s power to the transmission in relation to engine rpm. The main components of a torque converter are the cover, turbine, impeller, and stator. The cover is connected to the flywheel and transmits power from the engine to the impeller, which allows for torque multiplication and drives the transmission’s oil pump. The turbine is splined to the input shaft and driven by the force of the fluid from the impeller.
9. Valve bodies are normally fitted with three different types of valves: spool valves, check ball valves, and poppet valves. The purpose of these valves is to start, stop, or use movable parts to regulate and direct the flow of fluid throughout the transmission.
10. Reaction members are those parts of an automatic transmission that hold or drive members of the planetary gearset in order to change gears.
Fill-in-the-Blanks
1. Multiple-disc clutches, one-way clutches, friction brakes
2. Turbine, impeller, stator
3. Gear, rotor, vane
4. Hub, shell
5. Road, valve body
6. Supply, pressure, operate, lubricate, cool
7. Pressure-regulating, flow-directing
8. Electronically, throttle pressure, vacuum modulator
9. Sense, respond, driver
10. Speed, load, speed
Multiple Choice
1. C
2. D
3. D
4. A
5. C
6. C
7. C
8. B
9. C
10. B
SHOP MANUAL, PAGES 112-113
ASE-Style Review Questions
1. C
2. A
3. D
4. C
5. B
6. C
7. C
8. D
9. B
10. A
ASE Challenge Questions
1. C
2. A
3. C
4. A
5. B
Instructor’s Guide to Accompany Today’s Technician: Automatic Transmissions & Transaxles 3E 23