Copyright by Goodheart-Willcox Co., Inc.
364 Automatic Transmissions and Transaxles
Note: Some newer transmissions and trans-
axles do not have a dipstick. Check the
owner's manual or service literature for
checking procedures. Some vehicles without a dipstick
have a level sensor, and a scan tool must be used to
check fluid level. Some vehicles require the use of a
scan tool to ensure that the transaxle fluid is at the
proper temperature for a level check. On other trans-
missions or transaxles, the fluid level is read by noting
whether the fluid wets the bottom threads of the fill
plug, similar to the checking procedure for a manual
transmission or rear axle.
Introduction
Automatic transmission service is a specialized activity
that requires extensive knowledge and careful work habits.
This chapter will outline the automatic transmission/trans-
axle service procedures that can be performed without
removing the unit from the vehicle. If you have studied the
information in previous chapters, you will be familiar with
the components and tools discussed in this chapter.
Remember that the information in this chapter is gen-
eral in nature. Since there are many types of automatic
transmissions and transaxles, you should always consult the
appropriate factory service manual for the particular unit
you are working on.
Quite often, an automatic transmission will not require
a complete overhaul. The subassembly repair techniques in
this chapter can be used to service many transmission or
transaxle parts without the removal or complete teardown
of the unit.
There are a number of service procedures that can be
performed without removing the unit from the vehicle.
Obviously, checking fluid level and condition is one; so is
changing the fluid and filter. Adjustments to linkages, the
neutral start switch, and the transmission bands are also in-
car service procedures.
There are still other service procedures that can be
performed while the transmission or transaxle is installed in
the vehicle. The speedometer pinion gear, rear seal, vacu-
um modulator, oil cooler lines, extension bushing and out-
put shaft bearing, governor, parking gear and parking lock
components, valve body, and accumulator piston can all be
serviced without removing the unit from the vehicle. See
Figure 15-1. Many of these procedures are covered in
Chapter 17, rather than in this chapter.
material from internal parts. Contaminated fluid can cause
rapid part wear and premature transmission or transaxle
failure.
The most common hydraulic system problem is a low
fluid level. When the fluid level is low, air from the oil pan
can enter the hydraulic system through the pump intake.
When the hydraulic system contains air, hydraulic power will
be wasted compressing it. The air will compress instead of
moving valves and holding members. The unit will shift
erratically, or it may slip or fail to move the vehicle. The
remaining fluid will become overheated. Proper lubrication
will not be maintained, and parts will be damaged.
If a transmission is overfilled, the turning planetary
gears will churn the transmission fluid into foam. The foam-
ing fluid contains air, causing the same hydraulic system
problems as a low fluid level. In addition, foaming can
result in fluid escaping from the transmission vent, where it
may be mistaken for a leak.
In addition to the problems previously mentioned, the
introduction of air into the ATF results in severe and rapid
oxidizing of the fluid, which seriously affects the fluid’s prop-
erties. One result of fluid oxidation is varnish formation. This
problem appears as a sticky, burned-on substance that
resembles furniture-refinishing varnish.
To check the fluid level, locate the filler tube and dip-
stick. Remove the dipstick and wipe it clean. Then reinsert
it into the filler tube until fully seated. Finally, pull the dip-
stick from the tube and observe the level reading.
Figure 15-2 shows typical markings on a dipstick. The
fluid level should be checked as specified on the dipstick or
in the owner’s manual: generally at normal operating tem-
perature with the engine running, the shift selector lever in
park or neutral, and the vehicle on level ground. Some
dipsticks are marked so that the level can be checked with
the fluid hot or cold. Some transmission and transaxles will
have different readings in neutral and park, so always check
with the shift selector lever in the position recommended
by the service manual.
Note: No matter how well a vehicle is
repaired, the customer will be dissatisfied if
it is returned dirty or damaged. Always use
fender covers to reduce the chance of damage to
fenders from tools and belt buckles. Before entering
a customer’s vehicle, place a paper floor mat over the
driver’s side carpet to catch any grease or dirt on
your shoes. Install a steering wheel cover to reduce
the chance of getting grease on the steering wheel. If
there is any possibility of dirtying the vehicle uphol-
stery, place a protective cover on the driver’s seat.
Checking Fluid Level and Condition
Like engine oil, automatic transmission fluid should be
checked at specified intervals. Many manufacturers recom-
mend changing the fluid at specified intervals. The fluid can
become contaminated with metal, dirt, water, and friction
Fluid levels in automatic transaxles are sometimes hard
to read accurately. Many transaxle dipsticks will read high
when the fluid is cold, but after the fluid heats up, the dip-
stick will read less than full or even low. On some transaxles,