Fluid Change Can Cost Big Change ($)
Some of us may remember how in the days of
old a C-6 transmission would leave a beautiful filter footprint
in the bottom pan. This resulted from the filter opening being
too close to the pan. When the pump started sucking, it would
pull the pan right up to the filter, and as it vibrated away
the filter etched itself into the pan. Of course, that starved
the pump and caused premature failure of the transmission.
Sometimes this already-bad scenario would
be aggravated by an R&R technician’s use of a block
of wood between the transmission jack and the pan to lift the
transmission high enough to install the cross member. This
would push the pan right into the filter.
We have seen a similar method used with the
4EAT one- and two-pan units used in Ford and Mazda vehicles. If
they didn’t use a block of wood they used the jack itself
by closing in the four holding fingers and pushing up on the
pan in this manner. Sometimes you can even see dents left in
the pan by the four fingers.
Obviously, a procedure like this causes
unnecessary and premature failure of the transmission. And it
could be a mystery problem for some shops, leaving them
wondering why the pump is destroyed or the clutches burnt. This
can be a bit more elusive if the shop has one R&R man who
doesn’t use this method of installation but another does.
So only some units come back.
One other area that can cost you, if you
are not careful, is a simple fluid-and-filter change. How easy
it is to use an incorrect filter in a 4L80-E. In the 1997 model
year, the pan was made deeper and the filter inlet was extended
deeper into the pan. This filter has three dimples built into
the outside casing and a stand-off by the suction hole. These
dimples hold the filter up into the pump, preventing the filter
from falling out of the pump, and the stand-off keeps the
filter from sucking the pan up.
If you put an earlier-style filter into a
’97 or later unit with the deeper pan, the filter can
drop out of the pump. If you put a late-style filter into an
earlier pan, the neck can snap. Everything seems fine on a road
test and the vehicle gets delivered, only to come back with
unnecessary and premature failure of the transmission.
You must take care when replacing the fluid
and filter in 4L60-E transmissions in four-wheel-drive S10
Blazers. As you sneak the pan off to do a fluid-and-filter
change, or when you put the pan back after replacing the
filter, it is very easy to unknowingly damage the shift
solenoids. You fill the unit and start the vehicle, and it
immediately goes into failsafe with solenoid codes. Now the
shop has to drop the pan again and replace the solenoids.
Another filter mismatch that frequently
occurs involves both the AX4S and AX4N transmissions, in which
the filter seal needs to match the type of pan and pan gasket
being used. This can cause pump cavitation or falling out of
gear during turns. Eventually, it leads to unnecessary and
premature failure of the transmission.
The most-costly scenario we have run into
involves the 4L30-E, which has been on the road since 1990. The
internal solenoid wiring harness has a conduit made of plastic
that hardens over time from heat (see Figure 1). When you
replace the filter, you can push it up into the harness,
causing the conduit to break up into sections (see Figure 2).
This can expose a wiring splice in the harness, shorting it to
ground on a valve-body bolt (see figures 3, 4 and 5).
In 1990-93 models, this causes the computer
to initiate failsafe and report solenoid circuit codes that it
didn’t have before the fluid-and-filter work was
performed. This may cause you to spend unnecessary time and
money replacing the solenoids, which does not ultimately repair
the problem.
And as costly as this simple job has
become, it is not as costly as what can happen with 1994 and
later vehicles. For 1990-93 vehicles, this splice is the common
ground for the solenoids, and the TCM energizes the solenoids
on the power side.
In the 1994 model year GM changed the TCM
so that this splice is the common power for the solenoids and
the TCM energizes the solenoids on the ground side. So if this
splice gets shorted to ground during a fluid-and-filter change,
as soon as you turn on the ignition, this power wire’s
direct short to ground immediately destroys the TCM. This is a
very expensive fluid-and-filter change for the shop.
Now it’s time to fill the
transmission with fluid. With regard to rear-wheel-drive
vehicles, it may be a good idea to locate the full mark on the
dipstick. We have seen use of incorrect or mismarked dipsticks
on which the full mark is too low. It must be near or slightly
above the level of the pan gasket. Sumps that run slightly low
during highway cruises will cause mysterious clutch failure.
Have you ever dropped the pan on a 4L60-E transmission that was
not leaking, yet the pan was halfway down before any fluid came
out? Have you seen 3-4 clutches burnt for no apparent reason?
Every aspect of transmission work requires
skill, observation and common sense, even with something as
simple as a fluid-and-filter change. Otherwise, it could turn
into a costly experience – and we haven’t even
approached the subject of which fluid to use. Did I just open a
can of worms? 
©2006 Transmission Digest