Toyota 4Runner Topsites

Automatic Transmission Flushing




There are several subjects that tend to be a never-ending source of confusion.  One that constantly comes up is changing or flushing the transmission fluid in the Toyota truck transmission.  As usual most of the people that are confused and causing the confusion are Toyota Certified Technicians and service reps. 

I have learned a lot about the transmission on my 96 4Runner and would like to share what I know and I hope it cuts down on some of the confusion. 

The transmission on the 4Runner/Tacoma is not made by Toyota.  It is a nice, high quality unit that is used by several vehicle manufacturers including Jeep.

I have seen the inside of my transmission while it was torn down at Level 10 having its upgrades installed.  When it was reinstalled in my truck with its new performance torque converter, Level 10 put in 12 quarts for fluid.  When I got home I put another 3 quarts in to bring up to the full mark.  Now if you were counting that is a total of 15 quarts of fluid.

If you decide to change the fluid like you should, you cannot get all the fluid out by draining the pan.  When you drain the pan through the drain plug you will only drain about 3 of the 15 total quarts.  That is not much of a fluid change at all.  Most of the fluid is inside the torque converter, transmission cooler and the cooler lines.  Some vehicles like Mercedes have a drain plug on the torque converter so it can be drained, but not on our Toyotas.  There is only one way to get all the fluid out of the transmission so you can replace it with new fluid.  That is to flush it. 

There seems to be as much bad info out there about transmission flushes as there is about synthetic motor oil.  The number of professional mechanics that claim that a flush will blow out the seals and cause damage to the transmission dumbfounds me.  Those poor people are suffering from invincible ignorance and refuse to understand the benefit of a proper transmission flush. 

Here is the BIG secret about transmission flush machines.  They do not use pressure at all.  They use the transmissions own pump to move in the new fluid that displaces the old fluid and the old fluid is collected and thrown away.  There are two basic types of flush machines and here is how they work and the differences in the two.

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Cooler line flush machine:

The first type of flush machine connects into the transmission cooler lines.  BG makes this kind and here is how it works.  The line going from the transmission to the transmission cooler is disconnected and connected to the machine line in.    The line out from the machine carrying new fluid is connected to the line going to the cooler.  There is a chamber on the machine that has a diaphragm in it.  The top part of the chamber above the diaphragm is filed with new fluid.  The engine is started which turns the torque converter and the input shaft on the transmission.  The input shaft turns the transmission pump and it makes hydraulic pressure.  This causes fluid to flow through the cooler line.  As fluid leaves the cooler line it enters the chamber on the flush machine.  As the old fluid side of the diaphragm fills it pushes the diaphragm up and forces new fresh fluid into the transmission.  After a while the old fluid is collected in the machine and it is replaced by new fluid.  Now the transmission has been flushed.  Really pretty simple.  As you can see the machine cause no pressure and all fluid transfer is done by the transmission’s own pump. 

Here is what I do not like about this type of machine.  When the fluid leaves the transmission pump it passes to two different pressure regulators.  One regulator supplies fluid at one pressure to the transmission itself that operates the pistons and controls gear shifting.  The other is supplies the torque converter and the transmission cooler.  So you can see that all the fluid leaving the pump does not go to the cooler.  A bunch of it is cycled through the transmission and dumped back to the pan without going through the cooler.  This type of flush machine does not remove all the old fluid, but it continuously dilutes it down with new fluid.  It never really removes all of the old fluid, but is far superior to just drain and fill.

The other thing I do not like about this type of flush is that they sell the supposed benefit that they do not have to drop the pan and change the filter like that is a benefit.   Dropping the pan is very important.  Looking in the pan is a fantastic diagnostic tool that can tell you if something is going wrong in your transmission. Now lets say some crud is flushed out of the trans with this flush method.  Where does it go?  It can go into the pan, and then sucked up into the filter that may clog the filter causing the pump to starve for fluid and a pressure loss.  On the engine the filter is after the pump and if the filter gets clogged there is a bypass valve that opens and oil bypass the clogged filter so the engine is still supplied with oil.  Unlike the engine oil pump and filter the filter is on the intake side of the pump.  If it gets clogged, that is it, it is clogged and stuff does not get lubricated and the clutches do not get enough clamping pressure and they slip and burn up.  In just a faction of a second you just bought a new transmission if the filter clogs.

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Pump inlet flush machine:

Now lets talk about the type of flush machine I like.  This kind attaches to the pump intake after the pan and filter is removed.  This machine only supplies fresh new fluid to the pump intake and as the fluid passes through the transmission it dumps out to a collection tray and never goes back through for a second pass.  All of the old fluid and crud is GONE and replace with fresh new fluid.  After the service a new filter is installed, the pan replaced and then it is topped off with new fluid to the proper level on the dipstick. 

This process takes a total of 20 quarts of fluid to flush out 15 quarts of old fluid, replaces the fluid, and gives the mechanic the opportunity to look in the pan for anything unusual that would indicate a pending failure.

Everyone should have this type of service done every 30,000 miles, but definitely before your truck goes out of warranty.  By looking in the pan you may get an indication that you are about to have transmission trouble that might show up right after you get out of warranty.

I will tell you that this type a flush does take more effort and makes more of a mess, costs a little more, but I think it is worth it.

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Now the last big question that remains is what type of fluid to put back in, conventional or synthetic.  For lots of different reasons that is an easy answer, synthetic.   Premium synthetic fluid will lubricate the transmission better, provide better traction to the clutches, removes heat better, and not break down as fast under high temperatures.  Premium synthetic ATFs will protect better and last 3-5 times longer then conventional ATF.  When my transmission with being reinstalled in my truck at Level 10, I asked Pat the owner what he thought about AMSOIL ATF.  He said that is was the very best ATF in the world.  I will let you guess what I use.

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Filter and pan gasket:

The filter should be changed with the fluid, just like motor oil filters.  I got an e-mail from a guy that said he was told by a Toyota Service Rep that there is no filter in the transmission.  The amazement continues.  There are some transmissions out there that do not have replaceable filters, but this is not one of them.

When the filter is replaced it has to be done with care.  There are three ports on the filter where the fluid passes into the transmission.  Each has its own gasket.  It is common for at least one of these gaskets to slip out of position during installation and cause air to leak into the pump pick up causing it to break suction and loose output pressure.  The problem usually presents after hard stops and the transmission will not complete its shift into first.  Then when you go to pull off the engine revs and then the transmission engages very harshly with a tire chirp.  Just make sure they are all properly positioned during replacement.

The pan does not use a gasket, but many shops will try to install a cork one.  Toyota uses their own seal packing material that is available from the parts counter.  It is similar to RTV.  They have two kinds, black and red.  The black is for the engine and water pump and the red is for the transmission.  I use something that I think is a little better.  It is made by Permatex called “Right Stuff” and comes in a cheese whiz can.  This is fantastic stuff and does not require any drying time before you refill the transmission.  It is available from most parts stores.  Be careful when reinstalling the pan bolts, as they are easy to strip.

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When not to flush:

Before draining or flushing you should pull the dip stick and look at the fluid.  If it is dark, burnt smelling, and you see little flakes or speck in it, DO NOT FLUSH IT.  The fluid and transmission is TOAST, but the transmission just has not figured out it should die yet.  In these cases for reasons no one has figured out yet, if you flush a transmission in this condition it will fail right away.  Real strange, but that is what seems to happen. If your trans is in this condition just drive it while you save for a replacement transmission.  There is no way of telling when it will fail.  It might be today, next week, or next year, but it is doomed.

The goal here is to flush the trans BEFORE the fluid gets rancid.  What you are taking out should look like what you are putting in.  Do not wait for a color or smell change.  My 4Runner Owner's Manual calls for transmission fluid change at 30,000 mile intervals.  The industry standard it two years OR 24,000 miles which ever comes first.  It is your truck, you decide what is best for you.

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