Best Way to Change Transmission Fluid?

Hello stubby:
having long resistant automatic transmissions I'm not an absolute authority, however in my old age I have broken down and bought something with an automatic transmission.
My previous experience with automatic transmissions has been that removing the pan and cleaning out the debris and changing or cleaning the filter is an absolute must. In the old days there used to be drain plugs on the torque converters, somehow automotive manufacturers in their wisdom have done away with that, so a substantial quantity of transmission flood never gets changed in less you disconnect one of the cooler lines and flush the system.

When I get ready to change the transmission fluid in my truck I intend to remove the pan and change or clean the filter, and then remove a cooler line and flush the system myself, undoubtedly there will be a little mess but a large funnel, and an adequate supply of open transmission fluid along with someone to start the engine and shut it off should do the job, whether it or not it's actually worth the extra trouble I couldn't say however automatic transmissions are very expensive to rebuild nowadays so to me it is.

Obviously you will never get a completely virgin fluid content for the transmission without going too prodigious quantities of transmission fluid, but you should be able to hit 90 to 95% virgin content without much trouble.

PS: I don't know what their special machine is, but basically this is the way they do it when they flush the system, they just pump more transmission fluid in instead of pouring it, doesn't seem to special to me.

GA!

The auto tech said they just have an adapter that connects to the dipstick tube. That made me think it was simply a 'siphon action then refill' method.

I actually went to another shop and they said the same method was used. It makes me think there are a large number of shops doing the procedure incorrectly.

I believe I will stay with the 'tried and true' method for now until I locate a Pro like you.

A good shop with competent mechanics, and a quality machine will hook into the cooler lines with the machine. This method gives the best flush results, although I'm not familiar with the "sucking it out of the dipstick" method. Just from common sense, I would guess that sucking oil from the dipstick tube is in no way any better than a simple drain n change.

Without hooking up at the cooler, you wont get the cooler, cooler lines, etc flushed out. It is Definitely worth knowing a good competent shop/mechanic to do your repairs. After working in the industry for a bit, I can absolutely attest that an alarming number of service shops out there are less than adequate, and charge twice as much as they should.

all these points are good

I've been ASE Master since '79

if you flush (disconnect a cooler line and pump/recover) on a reasonable schedule, the pan clean and filter change is unnecessary

if the fluid is (burnt, or oxidized) damaged, the full sequence is necessary

Pretty questionable whether you are going to get the torque converter empty anyway, but if you keep changing regularly, well you get the point.

I've always been big on the screen and trash method of changes (since I found out it ever needs changing), but I am hardly an expert.

As for special machines, you can only do this two ways if you don't drop the pan; you either "flush" with the cooler lines or you drop a vacuum down the pickup like the speedy oil change shops do.

Given the circumstance you describe tho (on the road, overdue, and no tools) he is better off with a drain and refill than nothing. Some Harbor Freights offer the vacuum device advertised for oil changes, just a lightweight pump, resevoir and long hose. Probably good for three uses, but cheap enough to be discardable given the circumstances.

Hi Stubby,

Why are YOU doing maintenance on your SON'S car? Is he paying you to do it because he doesn't have the time?

Just curious.

Mike

Thanks! I did a search in CR4 before I asked the question and your previous post did not show up in the results. :(

on your jimmy i think that the mechanic will have to unbolt the trans mount and lift the transmission up a couple inches so the pan can clear the transmisson cross member this will add to the labor of the job, many times that mount will be broken and need to be replaced anyway. i would also ask to have a drain plug installed in the the pan. then every 2 or 3 engine oil changes you can change the trans fliud. this will increase the life if you transmission and make it a less labor intensive job to get at least some of the oil replaced occasoinally. the flush methods will probably do a little better job of changing the fluid but a partially plugged filter will lead to disaster. also dropping the pan and cleaning out what ever is in there give you a better idea of what shape the transmission is in to start with. more than a table spoon so "stuff" will probably mean rebuild now or take a real chance of getting stuck behind a wrecker. replacing the fluid with valvoline max life will help relieve worries about hard seals and worn clutches.

Oil changes on boats with inboard engines are generally done with a tube through the dipstick. This is because of the limited access to drain plugs under the engine. Off course this refers to engine oil changes not automatic transmissions. This doesn't answer your question, but it sounds that reply #2 makes logical sense.

Greetings.

The easiet way to change auto tranny fluid is to find the top line from the transmission to the radiator and disconnect it.

Run a rubber hose from the disconnected line to a 5 gallon bucket on the ground.

Start the engine and the fluid will start to come out into the bucket. This is best to do with two people (you and your son).

When the fluid starts to sputter turn off the engine.

Add 1 quart of fluid to the transmission (I suggest you use 100 % synthetic, I prefer Amsoil which starts to evaporate at 600 degress F and leaves no junk deposit behind. Regular petroleum based tranny fluid starts to burn at ~ 285 degress F and leaves a carbon deposit that seems to foul up the little bitty passages).

Start the engine again until the fluid coming out of the hose is the same color as the fluid going into it.

You have now changed all of the fluid in the transmission and the torque converter. A lot of times the places that change tranny fluid only change the fluid in the transmission and never in the torque converter.

Oh yea usually the fluid coming out of the transmission will make you wretch if it has started to burn so best do this outside.

Just a few points:

Unless you have been replacing the tranny fluid all along, at regular intervals, I suggest to not do it. If the fluid was never changed in 50K miles, I would leave it alone. With transmissions with wear and tear that have not been flushed over the years, there is a common danger to create problems for yourself (usually with older transmissions and non serviced ones) by replacing the fluid. Flushing a transmission (especially improperly) will tend to move the crud everywhere else in the transmission. I have unintentionally had to do this on a couple of older cars, when the pan gasket leaked or in one case, my girlfriend at the time ran over some gosh darn thing that killed the pan. She still insists she doesn't know what it was.):

If you want to properly flush it, you need to take off the pan.

You should take off the pan so you can check the magnet for sediment. That will most likely tell you the state of wear on your transmission, and you can change the screen as well.

Do not forget that the transmission fluid is cooled by the radiator, so if you do not flush it properly, you will not properly clear all lines, the pan, etc.

The first thing I would do is look at the fluid now, what color is it ? How much if any sediment is in it ? And how many miles on this transmission ?

I just had mine done that way this weekend for $89. I had this done to my daughter's vehicle a few months ago because her tranny was slipping and giving her problems. I figured this was an inexpensive test before spending the big bucks to have the tranny rebuilt. Her car works great now. There are drawbacks I suppose compared to taking out the filter and dropping the pan but this type of service has worked very well over the years for all of my high mileage vehicles.

they use these evac machines because mech's always forget to tighten the drain plugs!

in the long run big shops see less complaints

I had installed a drain plug figuring I could drain and fill the oil a few times in a couple of weeks and get a fresher change, and it worked well, no leaks. When it was finally time to have the trans rebuilt, they removed the plug and welded it up. I got the lifetime warranty for it (and used it three times) and I think they were concerned that the plug could get ripped out and drain all the fluid before I knew it and burn up the trans.

yes, rather than undoing the pan and replacing the filter and cleaning the pan and magnet, the flusher pretty much takes all of the fluid out of the transmission and at the same it it gets through every port on the transmission and does a more thorough job. the chances of you getting other cars transmission fluid in your transmission is very unlikely. the machine has two reservoirs, one for old/used fluid then the other brand new fluid so if anything you are getting fluid that is new but has been sitting in the machine since the last use. it is definately worth doing because you will get longer life out of it......when the shop uses that machine ask them to replace the filter and clean the pan before doing it.