1. Automatic Transmission Diagnosis and Service
Chapter 74

2. Objectives Perform maintenance service on automatic transmissions
Diagnose automatic transmission problems and recommend repairs
Change the transmission fluid and filter
Repair automatic transmission leaks
Perform basic automatic transmission tests
Understand what is involved in a transmission overhaul

3. Introduction Major transmission repairs
Done by specialty dealers or businesses
All technicians should be knowledgeable about repairs and diagnosis
Transmission needs major repair
Must be removed
Complicated specialty area
Special schooling is recommended

4. Automatic Transmission Identification and Maintenance
Important considerations
Transmission identifications
Locate identification label
Use wall chart provided by transmission part manufacturers
Automatic transmissions generally require very little maintenance
Transmission should last 100,000 miles or more

5. Transmission Fluid Service
Automatic transmission fluid (ATF)
Most are dyed red
Low viscosity
Contains additives
Several types
Long lasting
Severe service
Anything that causes heat
Example: trailer towing

6. Fluid Level Important considerations
Dipstick is in tube extending from transmission pan
Level should be between the add and full marks
Low fluid level is caused by a leak
High fluid level can result in foamed fluid
Conditions for checking fluid level
Car on level ground
Engine and transmission warm
Parking brake set
Gear selector is in park position

7. Check Fluid Condition Conditions Adding fluid
Milky fluid: coolant and fluid mix together
Varnish: dipstick will not wipe clean
Fluid has become oxidized
Burned fluid: dark with burnt smell
Adding fluid
Be sure to use the correct type
Use a clean funnel

8. Changing Transmission Fluid and Transmission Filter Service
Important considerations
Check the service manual before changing fluid
Electronic transmissions are more sensitive to problems with fluid condition
Transmission flush machines are a common
Pan must be removed to clean or replace filter
Draining the fluid requires removal of the pan
Inspect inside of pan for pieces of friction material or metal particles
Check the screw holes in pan

9. Remove and Replace the Filter and Refill the Transmission
Important considerations
Important: pump must suck only fluid and not air
Some filters have a gasket
Be sure to remove old O-ring or sleeve
Lubricate new O-ring with ATF
Replace the pan and tighten screws evenly
Check the service information for fluid capacity and refill the transmission
Do not overfill

10. Diagnosis and Repair of Leaks
Causes of leaks
Front pump seal
Rear seal to drive shaft yoke
Shift lever shaft seal
Pan gasket
Extension housing gasket
External leaks
Obvious
Difficult leaks
Use fluorescent dye and black light

11. Leaks from the Converter Housing
Remove access cover on housing
Disconnect battery ground cable and remove starter
Oil leak from engine crankshaft seal could be the cause

12. Transmission Cooler Line Leak
Important considerations
Some mechanics cut out bad section and replace it with a length of fuel hose
Use transmission oil cooler hose
Both ends of the line must be flared
Better repair
Cut old section of line and replace with a union or install flare fittings with a short piece of reinforced hose with crimped threaded ends

13. VSS/Speedometer Drive Gear Leak and Shift Lever Seal Replacement
Important considerations
Mechanical speedometers have an O-ring seal that can leak
Many late-model cars have an electronic speedometer pickup
Shift lever to manual valve is sealed with a lip seal or O-ring
Sometimes it is necessary to remove the pan and valve body to remove the shift lever

14. Pump Seal Replacement
Transmission has a full round seal that rides on front of torque converter
Exposed to a good deal of heat
Transmission fluid pours out when seal fails
Pump seal replacement
Requires transmission be removed from vehicle
FWD procedures
Vary
RWD procedures
More straightforward

15. Front Seal Replacement and Pump Bushing Replacement
Front seal replacement: major steps
Remove and drain pan under torque converter
Remove old seal
Install seal on installer and drive it into the pump
Pump bushing replacement
Bushing in transmission pump supports snout of torque converter
Check service manual for procedure replacement
Often requires removal and disassembly of pump

16. Reinstalling the Transmission
Major steps and considerations
Install and bolt to engine
Engine and transmission must be touching each other completely before tightening bolts
Torque converter must be correctly engaged
Should be at least 1/8" between converter studs and flexplate

17. Rear Oil Seal and Bushing Replacement
Removal of extension housing seal and bushing on RWD vehicles
Remove drive shaft
Old bushing can be removed without removing extension housing
Use special puller
Bushing sometimes has an oil return hole
Must be aligned

18. Automatic Transmission Problem Diagnosis
Before condemning a transmission
Check for diagnostic trouble codes
Check condition of engine
Quadrant indicator might not be properly aligned
Perform a visual check of electrical connections
Talk to customer before test-driving
How transmission operates when cold
Check fluid levels
Use a road test checklist

19. Slippage Electronic transmissions Slippage causes
Have sensors input and output ends that can calculate slippage
Slippage causes
Low fluid level
Leakage in clutch pack or servo
Plugged pump inlet screen or filter
Problem with valve body

20. Transmission Drainback
Worn input shaft
Transmission slips on initial takeoff
Shift feel
Mushy or harsh shifts
Mechanical transmission problems
Incorrect shift timing
Shift chatter or torque converter clutch chatter
Sticking governor
Vacuum modulator diagnosis and adjustment

21. Transmission Drainback (cont’d.)
Additional potential problems
No upshifts
Wrong gear starts
Engine dies in gear
No vehicle movement
Backward one-way clutch
Internal hydraulic system cross leaks

22. Noises Causes of noise High or low fluid level
Gear or bearing wear or damage
Bad torque converter bushing
One-way clutch
Engine accessories can mimic transmission noise

23. Flexplate Characteristics Flexes inward toward engine
Converter normally slides forward during deceleration
Flexplate will allow movement of up to 0.080” to 0.100"
Cracked flexplate causes a knocking sound

24. Transmission Tests Include:
Stall test: used to determine if transmission is slipping or torque converter is defective
Pressure test: tells if transmission is experiencing internal leakage
Air test: used to check operation of various clutch packs and servos

25. Valve Body Removal and Transmission Adjustments
Valve body removed while transmission is in vehicle
Be sure it is cold
Check balls must be replaced in same position
Transmission adjustments
Linkage adjustment
Neutral safety switch/park neutral position switch
Throttle cable adjustment
Band clearance adjustment
Speedometer adjustment

26. Electronic Transmission Service
Important considerations
Some generic scan tools can work on different makes of vehicles
Electronic systems can self-diagnose electrical components and circuits
Be certain of cause of transmission failure before removing an electronic transmission
Computers in most vehicles use ground side switching with current limiting devices

27. Electronic Transmission Service (cont’d.)
Electronic transmission shift control: line pressure is changed to accommodate shifts
Current flow varies depending on number of solenoids energized at one time

28. More Tests Before Transmission Removal
Some tests are done in the service bay or on the road or dyno
Other tests done on the lift
On the lift:
Tighten the band all the way
Run without ATF for a few seconds
Perform air test of hydraulic circuits
Computer-controlled transmission
Do not remove until transmission is determined to be the problem

29. Hybrid Automatic Transmission Service
Important considerations
Many hybrids use conventional automatic transmissions
Serviced in traditional ways
High-voltage electrical system
Must be disabled before removing transmission
Unique automatic transmissions needing repair
Replaced with a complete replacement unit

30. Remanufactured Automatic Transmissions and Transaxles
Important considerations
Many dealers do not perform rebuilds
Remanufactured transmissions have become readily available
It is important that the correct transmission is acquired
Especially with imports

31. Transmission Rebuilding
Important considerations
Internal damage has occurred
Hard parts will be necessary
All soft parts are good: use inexpensive seal kit
Valve body is disassembled: lay out each piece
Remove snap ring from clutch pack and clutch discs
Replace old seals on piston
Seal rings fit into grooves on shaft that supports center of clutch drums
Check all bushings for visible signs of wear

32. Transmission Reassembly
Important considerations
Do not use moly assembly lube on a one-way clutch
Spring in the roller clutch is bimetal
Heat is an enemy
End play is checked with a dial indicator
Selective washers or shims adjust end play
Many transmissions have more than one end play adjustment
Torque bolts to transmission pump after final end play check