Here is an explanation of the problem of transmission failure after
flushing/changing old ATF:
Archive for Wednesday, November 15, 2000
Transmission Health Check: Situation Is Fluid
By Ralph Vartabedian
November 15, 2000 in print edition G-1 LA Times
An automobile’s automatic transmission–the technology-packed gearbox
that is built like a Swiss watch, controlled by a sophisticated
computer and cooled by a red liquid that looks like cherry Kool-Aid–is
all too often a repair disaster waiting to happen.
Indeed, a transmission failure will typically cost more than $2,000,
which in many cases is nearly as much as replacing the engine itself.
Once a transmission starts to disintegrate, there isn’t much you can
do except to replace the entire unit.
Dirty automatic transmission fluid is one of the big culprits in
failures, which have grown more common in recent decades as engineers
have made systems more complex, jammed them into smaller spaces and
reduced the amount of outside airflow that cools them.
These trends have made transmission fluid all the more important
because of the crucial role it fulfills. It must lubricate gears,
bearings and other moving parts. It acts as a hydraulic fluid that
operates delicate valves and transfers power in the torque converter,
which is a high-powered fluid clutch that connects the engine to the
gearbox. And it is the only coolant inside the transmission to
transfer out heat.
Unlike motor oil, transmission fluid must provide lubrication but not
be so slippery that bands and clutches inside the transmission would
be unable to grab and transfer power when they are supposed to,
according to Mark Ferner, an engineer at Pennzoil’s lube research
center in Texas.
As transmission fluid ages, it can oxidize or burn up. It starts out
clear with a reddish tint but can end up opaque or brown with an
acrid, burnt odor. Such signs are typical of transmission failure
because they indicate that the transmission is overheating. (Fluid
that loses its color but remains clear is not necessarily a sign of
impending trouble.)
As the fluid oxidizes, it becomes less slippery and offers less
protection to moving parts. It also makes the clutches and bands
inside the transmission more grabby, so shifting is more labored.
All the while, higher temperatures accelerate wear. It is also common
for transmissions to shed metal flakes, but the amount of flaking
grows as a failure approaches, and that can jam valves and abrade
moving parts.
A mistake some motorists make is to change the fluid for the first
time only after they think trouble is coming on a high-mileage car.
The new fluid–with its greater lubrication and fresh detergents–often
will cause clutches to slip and will loosen deposits that can jam
valves. So the new fluid may actually precipitate the failure of a
transmission that is on its last legs.
Auto makers and transmission fluid makers have introduced newer fluids
that are better suited to handling modern operating conditions. At the
same time, they have extended the recommended change intervals. For
example, Ford Motor Co.’s Mercon 5 and General Motors Corp.’s Dextron
3 are described as lifetime fluids.
But a lot of the country’s top transmission experts believe that
motorists who follow such advice are begging for trouble. It makes a
lot of sense to change transmission fluid every 20,000 to 25,000 miles–
about four times as often as the auto makers say.
Ferner, for example, changes his own transmission fluid every 12
months or about 12,000 miles, saying new fluid replenishes the
detergents, contaminant dispersants and friction modifiers that get
used up over time.
Sam Memmolo, a master mechanic with a repair shop in Georgia, adds
that spending $100 or so on a fluid change to protect a $2,000
transmission is “a no-brainer.”
*
Knowing what to ask for in a transmission fluid change is a little
more complicated than getting a motor oil change. Auto makers do not
provide drain plugs for transmissions, so garages have developed two
ways to do the job.
Traditionally, a mechanic unbolts and removes the transmission oil
pan, a messy job that often results in burnt knuckles. With the pan
off, the mechanic typically changes the transmission filter, which is
either a screen or a cartridge with a felt filter inside. A good
tranny man can tell a lot about the health of a transmission from
looking at the amount of metal flakes inside a filter. The service
costs about $65.
But this method leaves several quarts of dirty fluid inside the torque
converter. Some garages now offer an alternative fluid change, in
which the old fluid is pumped out of the transmission through a
coolant line. The cost is typically about $60 to $80.
Although this procedure results in a complete fluid change, the old
filter remains behind. But a transmission filter may not need to be
changed every 25,000 miles, because it will continue to allow
unrestricted flow.
A third option–which many transmission mechanics recommend at least
every 50,000 miles–is to spend $110 to $130 and have both services
done at once.
Post by Jerohma while back, I remember reading that RATHER than a flush, LS400 owners
should politely ask for ONLY a drain and refill ... due to the possibility
of causing more damage than it is worth. Urban myth or any truth? Thanks
for any insight
j
