How To Service Your Automatic Gear Transmission; Do It Yourself

The automatic transmission is one of the hardest working and most sophisticated parts of your car. The engine works most efficiently at a relatively narrow range of engine RPM, and only uses energy effectively at the middle of that range.

The transmission has to convert the engine output to speeds and torque so it becomes practical for driving. In the case of an auto trans, it has to make the adjustments automatically, using a complex system of mechanics and hydraulics.
Doing this places tremendous stresses on the auto transmission – force, pressure, heat and friction. This can cause tiny metal particles to come off the gears and other components, contaminating the transmission fluid. The more of these abrasive bits there are, the worse the fluid performs, causing greater wear.
It’s a vicious cycle you should break regularly to preserve your automatic transmission and its performance… or be prepared for major costs.
That’s why you need to service your auto transmission regularly – at least every 15 months or 25,000km and more frequently if you use your vehicle for towing or in environments that cause a lot of stopping and starting. Some models may also require more regular transmission servicing. Your transmission specialist can advise you on this.
How to Service an Automatic Transmission Yourself.

We have divided the servicing into 4 parts and we will walk you through them easily.
1. Determine Your Transmission's Levelling System
2. Draining Your Automatic Transmission
3. Levelling Your Transmission Fluid
4. Stay on the Level

1. Determine Your Transmission's Levelling System

There are three main ways which your automatic transmissions can be levelled with the correct amount of oil.
Dipstick, Levelling Bung and Levelling Tube. First of all establish what kind of levelling system your transmission uses.

If your transmission has a dipstick then you level the transmission in the same way you level your engine oil; by dipping the transmission and adding more fluid until the level is correct. This is the easiest and less common.
If your transmission uses a level bung, you will need a way of pumping the fluid into the transmission from underneath, and you will also need something to catch the oil.

The level bung will be somewhere on the transmission at a higher point that the drain bung, and the levelling process involves pumping transmission fluid into the box until it starts coming out of the levelling bung.

Please note: DON'T just guess which bit to undo when removing a sump or level bung. Some transmission have components fixed in place from the outside, and undoing these by accident will likely result in the transmission needing to be removed and dismantled, A levelling tube often sits in the hole through which the transmission should be drained, and must be removed in order to drain the oil.
Finally, we have the levelling tube. The levelling tube works in the same manner as the levelling bung in that you pump fluid into the transmission until it starts to come back out. The problem is that the levelling tube is often inside the drain bung, meaning you have to check whether there is enough fluid using the same hole you are filling it through. Needless to say, this is the most difficult (and messiest) way of levelling an automatic transmission.

2. Draining Your Automatic Transmission
Understand that, in a typical transmission oil service, you will only be changing about two thirds of the oil in your transmission. Gravity can only get so much of the fluid inside, the rest remains in places like the transmission cooler, the torque converter, and various places inside the transmission itself. You can have your transmission “power flushed” to be sure you’re getting a complete oil change, but that requires specialist equipment and is not something you’re likely to be tackling yourself (unless you own a garage!).

With that in mind, you will need to establish which is your drain bung, find something to catch your old transmission fluid (and have a responsible way of disposing of it), and the means to get under your vehicle.

If your transmission employs a dipstick or a drain bung, simply place your waste oil receptacle so that it will catch the oil and undo the bung. If your transmission uses a levelling tube, you will need to undo the levelling bung first, then wind out the tube as well.
Leave your transmission draining until the oil coming out slows to a trickle. You can leave it longer if you wish, but be aware that it will continue to trickle out for hours if you let it. If you really want to be thorough, you could leave it overnight to get as much oil out as you can, but given that the best you can hope for is still around two thirds of the total transmission fluid, it’s probably not worth it leaving for too long. There are many specifications of transmission fluid. Make sure you have the right one for your gearbox.

3. Levelling Your Transmission Fluid
Once you have drained the oil to your satisfaction, refit the sump bung (replace it if you want to be really thorough), unless your transmission uses a levelling tube, in which case just replace the tube.

Begin refilling your transmission with fresh fluid, ensuring the oil you’re using is the correct specification for your particular transmission. If you’re filling from underneath, pump the oil in while watching for the oil coming back out. If, in the course of filling the transmission, you are obstructing the levelling hole/tube, pause every so often to check that the oil is not trying to come back out. If your transmission has a dipstick, simply pour the oil through the dipstick using a funnel.

Once the oil is levelled… you’re nearly done.

You see, when an automatic transmission is running, it pumps the transmission fluid around the transmission system, including the cooler and torque converter. This is relevant to you because when the transmission is running, the oil level drops significantly as the oil is taken up into the system. It’s the oil level while running that you need to work with.

So. Once the oil is levelled, make sure your vehicle is in park, fire up the engine, and then do it again. This time, once the oil is levelled, you’re done. You can put everything back together and clean up the mess you inevitably made.

If possible, you should drive the vehicle, being sure to get all the gears, and then check the level again to be sure. However, as long as the level was not sitting on the minimum when checked, it should be fine. The specification of fluid varies from transmission to transmission. Do some research and make sure you're using the right fluid for your transmission.

4. Stay on the Level
It seems obvious, but it’s worth pointing out that in order to get an accurate reading of the oil level, your vehicle needs to be as close to horizontal as possible. This means no sloped driveways, and no jacking the front end of the car up.