This article was first published in 2006.
Maintaining your car’s automatic transmission is
probably one of the most cost-effective preventative maintenance steps you can
take. For the less than AUD$200 you can have a specialist flush the trannie
fluid and install a new filter to greatly reduce the potential for damage. And
if you need just a little bit more motivation, you only need to find out how
much it costs for a complete transmission rebuild – you might be shocked!
So what’s involved in a professional transmission
flush? Let’s find out...
We took our ’97 Mitsubishi Verada to one of South
Australia’s longest established auto transmission specialists, Bruce Cussans
Automatics. Bruce started his business in 1984 and has vast knowledge and
experience in the field – he’s the perfect person to give us ‘the good oil’ on
The first step in the transmission
service/flushing process is to take the vehicle for a test drive. This is an
important step to identify whether there are any faults that the owner might not
be aware of. In this case, our Verada had developed a thump when shifting into
third gear – more on that later.
Next, the transmission fluid level is checked to
help identify whether there are any leaks. While under the bonnet, Bruce also
removed our Verada’s externally mounted transmission fluid filter. Note that
many cars don’t employ a filter of this type – instead, a strainer or filter
element is mounted inside the transmission and is accessible by removing of the
transmission pan. Removal of our Verada’s transmission filter required prior
removal of the airbox snorkel.
Once removed, the original fluid filter is
examined for metal particles. Depending on the amount of particles, this might
indicate serious damage to the transmission.
The car is now raised on a hoist to make the task
of fluid drainage easier. Our Verada has three small bolts along the bottom of
the transmission case which are part of the valve body circuit. These bolts were
removed (allowing a small amount of fluid to drain) and a high-pressure air gun
was used blow out any remaining fluid and sludge. This process helps ensure the
transmission valve body circuit is clean and shifts are precise. The three bolts
are now refitted.
The majority of transmission fluid is drained by
removing a drain plug on the side of our Verada’s transmission case. As seen
here, Bruce uses a sheet of cardboard to guide the fluid into an oil pan
positioned below. At this point, we should point out that doing this yourself at
home can be an incredibly messy job!
Note that Bruce is keen to remove the transmission
oil pan wherever possible. This enables him to clean the sludge that’s settled
in the bottom of the transmission and allows visual inspection of the
transmission internals. Unfortunately, our Verada doesn’t have a transmission
pan so this was impossible.
After a few minutes with the drain plug removed,
fluid will stop pouring from the transmission and it’s a good idea to inspect
what’s been caught. Transmission fluid that’s in good condition is clean and has
a red transparency while old fluid has a black colour and a thicker consistency.
The darker and thicker it is, the more urgent the need for fluid replacement.
The fluid should also be free of metal particles and shouldn’t have a burnt
smell – this is indicative of a slipping transmission. Bruce says it’s also wise
to look for coolant mixed with the transmission fluid. Some vehicles are prone
to transmission cooler failure which can lead to coolant entering the
transmission. This contaminates the bonding materials used on the bands and
clutch lining and it’s likely a rebuild will soon be required.
At the same time, the removed drain plug is
inspected. In most cases, the drain plug is magnetically charged to attract any
metal particles that are suspended in the transmission fluid. Thankfully, our
drain plug was free of those metal particles...
The transmission drain plug is now cleaned and
refitted, a new fluid filter is installed (making sure the mating surfaces are
clean) and the transmission is filled with around four litres of flushing fluid.
In this scenario, flushing fluid is nothing special – it’s merely the name given
to conventional transmission fluid that’s used for the purpose of flushing.
Fluid is added to the transmission with the selector in Park or Neutral.
The old fluid still lurking in the torque
converter, oil cooler and associated lines is pumped into the transmission case
by starting the engine and letting it run for a few seconds. Shifting the
transmission through all gears also expels the old fluid in each individual gear
Again, the trans drain plug is removed and the
fluid is drained into an oil pan. As seen here, the fluid caught in the pan is
much cleaner than previously. In most instances there’s no need for another
The drain plug is once again reinstalled and the
transmission is filled to the appropriate level. The technique for checking the
fluid level varies from car to car – Bruce suggests checking the owner’s manual
for the correct procedure. In the case of the Verada, the level is checked with
the transmission in Neutral. Bruce points out that it’s important to pour the
trans fluid slowly – it’s much easier to keep adding small amounts of fluid than
trying to drain a small amount of excess fluid... Of course, make absolutely
certain that the suitable fluid is used for your particular transmission.
Our Verada’s airbox snorkel is now refitted, any
fluid dribbles are cleaned and the car is taken for a test drive. Job done.
Trans Flushing v Trans Flushing – the Debate
There are numerous ways to flush a
According to Bruce, the technique employed on our
Verada typically replaces more than 90 percent of fluid. If the fluid that’s
drained after initial flush still looks dirty, he will usually repeat the
procedure until the drained fluid looks clean.
On the other hand, some workshops prefer to use a
dedicated transmission flushing machine that forces the old fluid out under
pressure while simultaneously introducing fresh fluid. This is a relatively
quick and easy exercise.
The third approach is to remove the oil cooler
line that returns to the transmission and start the engine to expel the old
fluid. Using this process, it’s vital to ensure the transmission pump does not
So what’s the advantage/disadvantage of
Well, the flushing machine approach will typically
achieve the most thorough flush. The biggest downside of simply hooking up a
flush machine is there’s nothing learnt about the transmission – in many
instances, the magnetic drain plug and filter aren’t replaced and, if there’s a
serious trans problem, this could go unnoticed. The other disadvantage is,
typically, the transmission pan is not removed so there may be a layer of sludge
remaining in the bottom of the transmission. There’s also no visual inspection
of the inside of the transmission.
The technique involving disconnecting the trans
cooler lines achieves a similarly thorough flush. But, again, this is often
performed without removing the drain plug, filter and pan. There’s also the
added risk of transmission pump damage if the transmission is allowed to run dry
with the engine running.
Finally, the approach outlined here is the most
hands-on and gives the best indication of transmission operation. This is
especially the case where the transmission pan is removed (unfortunately,
impossible in our Verada). The transmission flush is generally not quite as
thorough, but it depends how many times the flushing procedure is performed.
Maintaining a regular transmission flush schedule will keep the fluid fresh and
So what’s our suggestion?
Undoubtedly, the dedicated flushing machine will
give you the most thorough transmission flush. But make certain that, as part of
the procedure, the drain plug is removed, the filter is replaced and the
transmission pan is dropped allowing removal of sludge and visual inspection of
the transmission internals.
Third Gear Thump
A thump into third gear is apparently quite common
in Mitsubishis of the late ‘90s. While the trans flush will almost certainly
improve shift quality across the board, the real problem is with the Mitsubishi
transmission electronics. The industry ‘fix’ is to disconnect the battery for a
few seconds, reconnect it, start the engine and cycle the transmission from
Neutral to Reverse and Neutral to Drive at least five times. This process serves
to reset the ECU that controls the transmission and let it relearn the sensor
signals for each gear position. Shift quality will continue to improve over the
next few kilometres.
Results and Price
After a transmission flush and ECU reset, our
Verada no longer thumps into third gear and overall shift quality is noticeably
improved - but only just. And, now that we know the trans is in good condition
and has fresh fluid, it’s important that we make an effort to keep it serviced
Bruce Cussans typically charges around AUD$130 for
a basic transmission service which comprises a fluid refill and, where
appropriate, a new filter and removal of the transmission pan. This price varies
depending on filter price, fluid price and labour. The flushing process, which
will to achieve a more thorough fluid change, adds around AUD$30 depending on
fluid cost. The ECU reset on our Verada typically adds another AUD$30.
For under AUD$200 it’s a wise
Contact: Bruce Cussans Automatics +61 8