First - about that plastic thingie in the pan

Contributed by Scott I.

I read your section about the transmission fluid change. I feel that you should add this to it. Its about the small tan plastic plug I found in the pan. It's about 1.5 inches long with a O-ring it and small 1/4 inch rod about 1 inch of the total height. It is used to plug the dipstick hole when building the transmission and gets pushed in the trans when the dipstick is added. I have beat my head on the wall till I found out what it was for. Most people that read your page probably had their first transmission service done by the dealer and the plug was thrown away.

Changing Your ATF at Home

Contributed by drbob

First, let me share the method behind my madness. Regulars have followed the discussions on the Jiffy-Lube machine that attaches to the transmission cooler lines, force-feeding new ATF into the return hose while capturing the old fluid that is piped to the cooler. Sounds simple -- just put a quart of fluid in the return line for every one that's pumped out. It -is- simple, but it's also about $60 plus the cost of your ATF if you don't like their flavor. Since I wanted Synthetic ATF, I would have had to buy it at a transmission oil store and bring it with me.

This method allows all the fluid to be changed in one pass. A 'normal' transmission fluid service changes about 3 quarts of fluid along with the filter. That leaves some 7 to 9 quarts of fluid in the rest of the transmission that doesn't get changed. So in reality, you are just diluting the old fluid with new, and you're always stuck with a pretty good load of old fluid in there. The improved method gets virtually all the old fluid out.

While reading the Ford service manual, I stumbled onto a procedure for testing the ATF flow through the coolers. The suggestion is to pull the return hose off, connecting a new longer hose so that the oil can be recirculated back into the transmission through the dipstick/filler tube. You run the car, and look to make sure a lot of fluid is flowing.

So the eyes in my "head saw the world spinning round", so to speak. My theory is that if you can do this test, you could just as easily put the hose in a calibrated bottle, adding new fresh fluid into the filler tube at the same rate that it is accumulating in the bottle. I ran the idea past a few transmission specialists, who all thought it a good idea.


So here's the step-by-step account of what to do (and what not to do) to make this work for your car.

Things you'll need:

  1. About 16 quarts of transmission fluid. I wanted to use the Mobil-1 synthetic ATF, so I fudged a bit by putting the first few quarts in using conventional Mercon followed by 12 quarts of Mobil-1. The Mobil-1 was about $4 a quart at the local Auto Parts Club, and is $5 a quart at Chief Auto, so the total bill for this part is $50 to $60.
  2. A section of reinforced 5/16" transmission cooler hose. You can sub in a good high-pressure fuel hose for this. You'll need a few feet of this to make things convenient, and a good screw clamp.
  3. Several 'calibrated' plastic milk bottles. I measured even quarts of water into a milk bottle, and marked the levels on the outside with a felt marker. Make similar marks on all the bottles.
  4. I have a tool called a 'hose pincher' that I picked up at one of those discount tool stores. This tool allows you to adjust the amount of flow in the hose in small increments. If you have a good set of Vise-Grip pliers, they will probably work fine.
  5. A drain pan. The one you use for your motor oil will work fine. I also spread a bunch of newspaper around to catch any stray drips that would otherwise have to be washed down with soap and water later.
  6. Eye protection. With luck, you won't get any ATF anywhere but in the pan and the bottles. But with the pressures and the restrictions in the hose, there's a good reason to have your eyes protected.
  7. A helper who can start and stop the engine on command.
  8. One long-necked transmission funnel for adding ATF into the dipstick tube.
  9. Oil-Dri or some kitty litter to help with cleanup if you spill. I found some 5# boxes of STP cleanup at the local 99-cents store for (you guessed it!) 99 cents.

What to do:

I recommend that you do this with an engine that is not hot. An errant spray of hot ATF will leave a lasting impression. Don't tempt fate!

  1. The path of the fluid through the coolers takes it through the radiator cooler, then through the auxiliary cooler in front of the radiator. On my car ('92) the easiest place to attach your hose is to the steel line that carries the fluid from the radiator cooler, where the rubber hose to the auxiliary cooler attaches. Lying with your head under the front bumper, you'll see the two steel lines with rubber hoses attached where they pass under the bottom of the radiator. The rubber hoses continue on up to the auxiliary cooler in front of the radiator. One of those steel lines comes from the radiator cooler, while the other is the return line to the transmission. You want to attach your hose to the steel line coming from the radiator cooler, so look for the one that goes directly to the transmission, and then use the other one. On my car, this is the line on the left (driver's) side of the car. Put your drain pan under the hose connection, unscrew the clamp, and let the auxiliary cooler lines drain into the pan. Then securely attach the new hose section to the steel line with that screw clamp.
  2. Set up your bottles in front of the bumper on the floor. Place your hose pincher on the hose, clamped so that it almost completely shuts off the flow in the hose. Since you'll want to put the end of the hose in the bottom of the bottle, put the pincher far enough up the hose so that its weight won't pull the bottle over.
  3. Set up your ATF on a table with the caps removed. Give yourself room to work, but keep everything in easy reach. With the hood open, put your long-necked ATF funnel into the dipstick hole, and we're almost ready. Double-check your hose clamp, your hose pincher, your eye protection, and put the first quart of ATF in the funnel. I used the conventional for the first few quarts so this should be a conventional quart if you're as cheap as I am.
  4. Have your assistant start the engine while you adjust the hose pincher to a reasonable slow flow. I was amazed at the amount of fluid that flows in the cooler so be conservative on your initial setting. Watch as the fluid comes up in the bottle, adding ATF in the funnel to coincide with the amount that's coming out into your milk bottles. You want to stay a bit ahead of the outflow so that the pan never runs dry, but you don't want to get more than a quart ahead of the outflow.
  5. As the first bottle gets to the gallon mark, pull the hose and put it quickly get it into the next bottle. It's OK to stop the motor to do this transfer, as it will save you a bit of cleanup.
  6. Proceed to take 14 quarts of fluid out, and replace them with 14 quarts of new fluid. That's 3 1/2 milk bottles of ATF.
  7. If you want to be a purist and you have the ability, you can remove the other auxiliary cooler hose, and apply a little low-pressure air to the one that goes to the upper fitting. This will gently force the old resident ATF out through the lower hose into the drain pan. Use low-pressure air for this, and have patience. More air means more spray which means more mess.
  8. Reattach all the original cooler lines and hoses, drain the ATF from the new hose into the partial bottle, wipe up your dribbles, etc.
  9. Check the fluid level in the transmission. If everything went perfect, you are just a bit low, thanks to the oil you removed from the auxiliary cooler. Remember that the fluid is checked at operating temperature, engine running in park. Adjust the level as necessary.

Note the bright red color of the transmission fluid. Your transmission loves you for doing this service, flushing all the stale old fluid out.

Some thoughts on doing this procedure:

The amount of fluid that is normally circulated through the cooler is pretty amazing. Initially, I didn't realize that the hose pincher was going to be a requirement, and pumped a few quarts into the bottle before I could run back and shut off the engine. There's no way you can get the new ATF into the funnel and the pan fast enough to keep up with the open discharge flow.

I initially used some of that clear vinyl hose for the drain line. I thought it would be cool to see the old dark red stuff come out, changing color to bright red as I finished. The vinyl hose burst as I was finishing up, spraying a couple quarts of fluid all over the underside of the bumper and the floor. Trust me when I tell you that 2 quarts make a pretty good size lake under the front of the car. You can't run in that stuff either, no matter how fast you try to get around to shut off the engine. That's the reason I know the Chief Auto price on the Mobil-1 ATF-- I had to get cleaned up, and jump in the Subaru chaser to get a few spare bottles late at night.

This also illustrates the need for a helper to man the ignition key. Running the transmission pan dry of fluid is a real no-no. Having a helper also means that the engine is shut down quickly if you have another problem, like moving the hose among the milk bottles, or opening the next few quarts of ATF. Have patience, work slowly and carefully, and don't lose track of how many are in and how many are out.

The cooler return line doesn't dump directly to the pan. Instead, it provides lubrication to some of the components in the front of the transmission. During this procedure, there's minimum strain on these components running in neutral. So the lubrication that's left in there is enough to keep them OK for the short duration. It's still not a good idea to run the engine with the cooler return line disconnected for any longer than necessary to change the fluid.

The transmission filter needs to be changed as a part of a normal transmission service. After the frustration of cleaning up the mess from the hose break, I decided that the filter would wait for another day. The fluid and filter were changed last fall, about 10k ago, so for me this isn't too critical. But it will get changed sometime soon.

Is there a noticeable improvement in transmission operation? It's hard to tell. There's a tendency to say that it does shift a bit better/smoother, but it was shifting fine before. The real test will be with the boat hanging off the back, I guess. In the few miles I've driven it, just tough to identify any significant improvement in performance. This change was made in the interest of extending the useful life of the car, and not to fix some symptom of an upcoming problem. My feeling is that if I wait to see the first failure symptoms before I do the maintenance, I have failed in my long-term mission.

Once again, let me remind readers that the procedures listed here are suggestions and observations based on my own experience with my own car. They should not be construed as a recommendation, at least to the point where you might want to blame me for something that goes wrong. This information is shared for your reading pleasure, so that you can share vicariously in the fun of swimming around on the concrete garage floor in spilled transmission fluid. Perhaps with the right partner, it would be more fun. =8-)

If you follow the procedure above, you won't be bursting hoses and spraying ATF on the floor. When done this way, the job is much less messy than a normal transmission service with filter.

Use you best judgment before you decide to try this at home. Make sure you completely understand the procedure before you start, and be aware of the risks involved to both you and your car. Wear eye protection! Plan on spilling a little fluid, and make sure you are ready to handle problems as they arise. If anything happens, stop the motor!

The local Jiffy-Lube store will do the labor part of this procedure for about $60. It just seems like a lot of money to me (cheapskate!) for something I can do myself. But I recognize that not everybody wants to do this stuff, so don't feel bad if you decide to have it done by someone else. With the reports of failures that surface here in the group, it is cheap insurance, especially considering the $2.5k repair numbers that are discussed.

As usual, readers are invited to share opinions and experiences, suggestions and criticisms. Let us know how it works for you!

Reprinted with permission

Comments from Another

What you describe is similar to what I've done the last two times I've serviced my transmissions, one Chevy and one Explorer. All I did was unhook the cooler line, route it with an extra piece of large diameter hose to a 2.5 gallon distilled water container (empty of water). Then I started the engine and let it pump fluid out. When it started to show intermittent flow I shut the engine off. Then I filled the transmission back up with some new fluid, of the approximate amount that had come out and did the same thing again. My memory is a little hazy but it seems like I wound up using about 2 or 3 gallons of ATF but some of that got pumped back out. I wasn't really shooting for complete change but just didn't want to drop the pan because I'm not worried about the filter.

One thing I don't agree with is the idea that it's particularly important to change the filter. IF you regularly change the fluid there really isn't anything going on in the transmission that will put much "stuff" on the filter, it's really there just to make sure no big metal filings and clutch facing debris get recirculated. It's not at all like the purpose of an engine oil filter, which has to process oil full of all sorts of gunk. There really isn't anything going on in an AT to generate gunk unless you are abusing the thing and not regularly changing the fluid. So I don't worry about the filter until it's seen at least two fluid changes. But that's just personal opinion. I know some people will feel it should be changed and they are welcome to do so. It does partially defeat the labor savings of the "pump it out to change it" method of ATF oil change. I ripped up the old filter one time just to see what it had caught and basically there was almost nothing on it, the pan itself was pretty much clean too with just a small pile of clutch facing that had worn off that had sifted through a slot in the filter housing.

It's still a messy job; I wound up with the hose coming out of the jug and ATF getting all over. I'm tempted to let Jiffy Lube do it next time; if I use synthetic and they change it ALL out it really shouldn't need a change again for another 50,000 miles.

Contributed by Bill S.

I tried Dr. Bob's transmission fluid flush / change (which I was extremely glad was available). I had to make modifications because I do not have the same transmission cooling system as him. I do not have a cooler that is separate from the radiator. I own a 1995 explorer (Dr. Bob's is a '92). It has two transmission lines running to and from the radiator.

The modifications I had to make were as follows:

1) Since I did not have the extra cooler, I just disconnected the top transmission line (near the radiator cap). I also investigated the bottom one. I am not sure which way the fluid flows, but near as I can tell, it flows from the transmission to the top of the radiator out through the bottom of the radiator and back to the transmission. It would be best to hook up your hose to the bottom fitting on the radiator (which would allow you to get the fluid out of the radiator also), but that requires a special male threaded section. For the long term, I may try to hook up some kind of T-fitting that would allow me to shut off flow in one direction and route the other directions flow out to my bottle.

2) 5/16th hose was too small. I had to move up to 5 feet of 3/8th transmission hose. The flared ends on the tube kept me from getting 5/16th over the end.

3) I did not use a hose clamp to regulate the flow. Use of the clamp (or Vise-Grips) would cause fluid to flow the other way through the system - which meant it would flow out onto my floor pan. I found that the fluid did not flow too fast without the clamp. The use of a helper to turn the car on and off was a must.

4) I used a single large water cooler bottle instead of many plastic gallon jugs. I marked off quarts on the jug using water and a felt tip marker. The benefit is two-fold. The large water cooler bottle is very stable and would not tip over and it is also just large enough to never have to transfer the hose to any other container. This helps resolve the high flow-hose clamp problem (discussed in point 3) even more -- the container can handle the high flow.

The rest was pretty much the same -- just have your helper turn on the car. For every quart that is pumped out, add a quart to your transmission funnel. If the flow gets ahead of you, have your helper turn off the car.

Contributed by suki

Just my slight modification. Instead of a hose pincher, I used a 1/4" npt drain cock (~$2) that I found at Trak Auto. My setup is a high pressure transmission hose, the drain cock followed by a clear hose. Even though the pressure isn't very high when the drain cock is open, I use a re-enforced clear hose just to be safe. Anyhow, you can watch the ATF go by... There is a small drawback. I get a slight leak from the drain cock.

Contributed by Greg J.

I have a suggestion for the module on tranny fluid change - it is a variation of Dr. Bob's original idea. It can easily be done by one person working alone and doesn't have the risk of running the pan dry.

Here's the deal:

I have a friend who is a tranny tech who says that putting a clamp on the outflow of the oil cooler lines can generate very high pressures throughout the system. This has the potential to blow seals, etc. So best not to put a clamp on the outflow.

My method does not require "pinch-clamps", calibrated bottles, or putting the oil in a quart at a time. There is also very little mess. In fact, I stole the idea from looking at the T-Tech machine at Jiffy-Lube.

So, here is what I do. I attach transmission hoses to BOTH the "from transmission" and "to transmission" connections at the auxiliary cooler. I use about 10 feet each since I do this all by myself and can keep everything near the drivers door.

The difference is you use two 5-gallon buckets instead of milk bottles. In one, which is carefully cleaned and dried, I put 16 quarts of tranny fluid (Amsoil, naturally). The other is used to collect the old fluid.

Put both buckets near the driver's side door of the vehicle so you can watch them. Make sure you know which line is "in" and which is "out". If in doubt, tickle the engine with both hoses attached and the outflow line will shoot t-fluid.

Now put the "in" hose into the bucket with fresh fluid so the hose is near, but not touching, the bottom of the bucket and secure it to the handle with duct tape. Put the other hose into the empty bucket and tape it to the handle, too.

Now, start the engine. You will see the dirty fluid flowing into the empty bucket and the new fluid being sucked into the tranny. No pressure changes anywhere in the system!!! Run the engine until the new fluid just starts to pull air (about 2-2.5 minutes) and shut it down. Reattach the connections. Check the fluid level, check for leaks and you are done!!

The 5-gal plastic buckets are free at just about any grocery store if you ask. So, you are only out the cost of the hose, hose clamps, and fluid.

It also makes it easier to take the fluid to the disposal station.




Updated November 24, 2000

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