Automatic Transmission Failures
and Their Prevention
An article by Wilson Transmission
2752 E. Main Street Plainfield (suburb of Indianapolis),
Indiana written March 1999.
Transmission - Causes of failure
Automatic transmissions fail in as many ways as there are car
models. In contrast, there are only a few reasons why anyone needs
automatic transmission repair. I break it down into four major
categories: neglect, abuse, design flaws, and normal wear and
The number one area of neglect is inadequate routine maintenance. As
the temperature of the oil increases, the chemical components start
to break down. Over time, the lubricating properties of the oil are
lost. If not replenished, bearings and bushings begin to wear. If these
bushings and bearings wear out, they can cause internal leaks which
cause pressure losses, which lead to clutch, band and geartrain failure
requiring the need for a rebuilt transmission. Fluid and filter changes
(routine transmission service) should be performed at regular intervals
from 15,000 to 25,000 miles, depending on the type of use. Vehicles
used strictly for family transportation and for commuting to and from
work should be serviced every 25,000 miles. Vehicles used for fleet
service and medium duty hauling need servicing every 15,000 miles unless
an auxiliary cooler is installed. More about coolers later.
A thorough transmission service procedure includes a road test to check
for proper shift points, shift quality, inspection for external leaks,
proper throttle pressure adjustment, proper linkage adjustment, a look
inside the pan for abnormal signs of wear or damage, and finally replacement
of the filter and addition of new fluid. In case you're wondering, there
is no way to reasonably change all of the fluid. The pan usually holds
four to six quarts of fluid while the torque converter can hold up to
nine quarts. Most converters cannot effectively be drained without drilling
and plugging. Most vehicles don't allow access for this. Some older
transmissions have a drain plug in the converter to allow draining of
this component. Not even then will all of the old fluid be removed.
Some shops have recently invested in machines that claim to be able
to give your transmission a complete transfusion by connecting to the
cooler lines and pumping new fluid into the system while at the same
time removing the old. The problem with this procedure however, is that
the converter acts as a reservoir. As new fluid enters, it does not
force the old fluid out. Rather, the new fluid mixes with the old fluid
inside the torque converter before it can be expelled from the transmission.
In my opinion, to properly flush the system in this manner, one would
need to circulate two to three times the capacity of the transmission
through the system to get the job done. Even if this procedure were
100% effective, you would still need to remove the pan for filter replacement
It's kind of like "the best cure for snake bite is not to get bit."
The best answer is not to let it get ahead of you in terms of mileage.
Changing the filter and moderate amounts of fluid at regular intervals
saves the life of the transmission and keeps you away from the dreaded
In addition, all automatic transmissions use rubber or paper gaskets
and seals. When subjected to the ordinary heat generated inside the
transmission they shrink and become brittle. As this occurs, leaks develop.
If these leaks are allowed to go unchecked, low fluid level will result.
This will cause damage to internal components. So there is more than
one reason to let a qualified transmission expert service your vehicle
as opposed to just any auto repair shop.
This is an area of great controversy. What is abuse? Any type of use
that the vehicle was not intended for. How do we know what was intended?
We really don't know. If the manufacturers made an absolute statement
about intended use, they would expose themselves to litigation on the
In my opinion, any amount of extra weight that causes the driver to
notice a difference in vehicle performance is approaching abuse to the
degree that extra heat is generated. It's excess heat caused by extra
stress that dramatically shortens the life of your transmission. If
the heat cannot be adequately dissipated, then internal damage will
result. It's that simple. In addition to the extra heat being generated,
there's the extra load on all of the internal components. Clutches and
bands are designed to hold tightly under the load of the normal weight
and horsepower of the vehicle. Increases in either of these can cause
trouble. Now, I know that not using your 3/4 ton truck to pull the family
boat to and from the lake is not the answer you want to hear. But if
you want to preserve your transmission to the maximum extent, then that's
the correct answer. Personally, I pull my boat. But I don't do so without
taking precautions. Please consider the preventative measures listed
below. Transmission overhaul is getting considerably more expensive
these days. Preventative maintenance and proper driving habits are the
best ways to avoid costly transmission repair.
Transmission Design Flaws
This is the area that most people find the hardest to accept. How is
it that my new $28,000 truck could have design flaws that will cause
premature failure of my transmission? If a vehicle manufacturer were
to spend the time and money necessary to debug every facet of design,
that $28,000.00 truck would cost $128,000.00 or more. Why do Rolls Royce
and other comparable automobiles cost so much? They take more time in
designing them and then work out the little problems in the design before
they go to production. The government with all of its regulations, the
demand by the public to produce vehicles quickly, and plain old human
error simply make it impossible for any manufacturer to build anything
perfect. That's why you see so many changes in design during the current
model year and why TSB's (Technical Service Bulletins) exist.
Comfortable shifts, less strain on the engine by the transmission oil
pump, reduced weight of transmission components, and other parts of
the vehicle in order to conserve fuel, more heat and other factors,
all contribute to premature wear inside the transmission. To be fair,
most manufacturers have made great progress in improving transmission
reliability over the last 10 years. They are more dependable today and
last longer. But that doesn't mean they are flawless.
Transmission Normal Wear & Tear
Anything mechanical can, and will, at some point in time break down
or wear out. Transmission failure is no exception. Bushings and bearings
are usually the first components to go, with dynamically applied clutches
and bands following. Dynamic meaning a band or clutch used to stop something
in motion as opposed to preventing a stationary (static) object from
starting to move. A reasonable service life can be from 40,000 - 50,000
miles up to 150,000 miles or more depending on the type of use. General
family use on the high end. Fleet and commercial use on the low end.
Transmission Breakdown Prevention
First there's the heat problem. Installation of a good quality auxiliary
oil cooler is the first step. Why do I need an auxiliary cooler? Doesn't
the factory provide one for me? Most vehicles are designed to circulate
transmission fluid up to the radiator and back again through two steel
lines. The coolant inside the radiator is what cools the transmission
fluid. Yes, that's right. 200+ degree antifreeze tries to cool 300+
degree transmission fluid. Doesn't make a lot of sense, does it? Auxiliary
transmission oil coolers use the outside air temperature to cool the
fluid which is far more efficient. Sometimes, if your vehicle has a
towing package for instance, the factory will install an auxiliary cooler
on the vehicle. Otherwise you must order it as an extra accessory.
The addition of one of these coolers can more than double the life of
the fluid and the transmission. The best coolers, in my opinion, are
built by the aftermarket. Ask your local transmission shop about the
Second, on many late model vehicles, reprogramming the transmission
is also necessary in order to get enough fluid to the cooler, help the
bands and clutches hold better, and provide an increased volume of lubrication
oil to the geartrain. On certain 1997 and later domestic vehicles this
reprogramming has its limitations. Due to the way the computer controls
the transmission, changes made internally effect what the computer sees
and how it controls the shifts, sometimes canceling out the benefits
of reprogramming. To be sure, ask a qualified expert. By qualified,
I mean a technician who specializes in modifications and reprogramming,
such as shift kits, as separate transmission services.
I emphasize routine fluid changes. It's the single most important aspect
of preserving your automatic transmission and preventing the need for
a rebuilt or overhauled transmission.
For advice and service in the greater Indianapolis area by qualified
expert technicians in reprogramming by Transgo®, installation of Hayden®
oil coolers, and custom transmission repair, call WILSON TRANSMISSION
at 317-839-9955 or visit
our web page.