How to Change Automatic Transmission Fluid

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Changing your own automatic transmission fluid should be done every 20,000 to 50,000 miles. Luckily it’s quite easy! See how on this Autoblog.

Look at all our Autoblog videos for more tips on how to diagnose, repair and modify cars from professional detailer Larry Kosilla. While you’re at it, check out Larry’s other car cleaning and maintenance video series Autoblog details!

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Instructions (video transcript):

[00:00:00] [Narrator] Changing your automatic transmission fluid is easy and should be done every 20 to 50,000 miles for most vehicles that require maintenance, but check your owner’s manual to find out when it should be changed, what type of fluid is required, and how many liters the system holds before starting. Here are the tools you’ll need to do it yourself. Socket wrench and torque wrench, brake cleaner, catch pan, scouring pad, bucket, gasket adhesive, transmission fluid, gloves, safety glasses, basic tools, rags and funnel.

[00:00:30] I’m Larry Kosilla, a professional draftsman and trainer for 15 years, but when it comes to what’s under the hood, I’m the student. Follow me as experts teach me how to diagnose, repair and modify cars on Autoblog’s Wrenched. I’ve heard of quick lube places offering a transmission change, service, and even a flush. What is the difference between these two? – Well, a fluid change would be to drop the fluid, you put fresh fluid on top of it. A service would be to remove the pan,

[00:01:00] by putting in a new filter, then filling the liquid from the top. A flush actually cleans the torque converter fluid, which contains a few gallons of oil that you can’t drain by simply removing the pan, so one of the best ways to do this is to put in fresh fluid , put in a new filter, drive it for a while, you’ll get a lot of the old fluid out, mix it up, then drop it again. Now it’s hard because you have to do it twice, but it’s so easy you can do it yourself. – [Larry] Check the current fluid to get an idea of ​​its condition, smell, color, and level.

[00:01:30] Use the same colored paper towel now as you will later so you can easily compare transmission fluids. Make sure you have an empty box before starting this process. With the car in the air find the transmission and unscrew the drain plug or in some cases you will need to unscrew a few bolts on the pan and do what is called a slow drain before removing them all to avoid a huge mess. Fortunately, this car has a drain plug, which makes this process much easier.

[00:02:00] Now, with most of the fluid out, remove the transmission pan. With the pan out of the car, it’s now time to do some detailing. First, remove the previous gasket with a plastic razor blade or scouring pad, being careful not to gouge the flat surface which could cause a future leak. Clean the crankcase inside and out, the associated bolts and pay special attention to the magnetic filter. Just like oil drain plugs, transmissions also have magnets attached to the inside of the pan

[00:02:30] to attract metal shavings from the transmission when in use. It’s scary to see all the metal parts, but I’m told that’s completely normal. Look at the mating surface of the transmission and make sure it is as clean as the pan. This is an extremely important step for a perfect seal, so it shouldn’t be rough or bumpy, or have any gasket residue. Now that everything is clean and ready to go, it’s time to replace the filter, but it’s a good idea to make sure the old and new are exactly the same.

[00:03:00] Most filters will have a rubber seal, like this one here. Add new transmission fluid to the rubber for a better seal before installing and tightening. Then reinstall the pan, but a new gasket is needed to replace the old one we scraped off. Prior to adding a new gasket, a tacky gasket adhesive is placed on the mating surface to hold the gasket in place during reinstallation to prevent it from moving or slipping and possibly causing a road leak . Now install the pan carefully trying to avoid moving the seal,

[00:03:30] then hand tighten all freshly cleaned bolts. Once the socket head bolts are snug by hand, tighten them in a crisscross pattern to evenly crush the joint, much like tightening your lug nuts. In this case, it’s just a few more bolts. If you’re wondering where to find the torque specs for your car, you can easily check online or at your local dealership. Take the old liquid in your previously empty waste container and pour it into an old gallon or liter container to measure exactly how much was removed from the transexual.

[00:04:00] Be sure to properly dispose of used fluid. This is toxic and must be disposed of properly. Check your local auto parts store to see if they recycle or can recommend where to go. Add your funnel to the dipstick tube and replace the same amount of old fluid, but with new fluid. Next, start the car and, with your foot on the brake, shift gears to help flush clean fluid through the torque converter, which will flush out old fluid that was once trapped and left behind even after our first oil change.

[00:04:30] Now that the car is off, go back to the drain plug and drain the fluid again without removing the pan. You’ll see the clean liquid we put in a few minutes ago mixed in with the old one, and now everything’s gotten a little darker, but it’s definitely better than our old liquid or stock liquid we once had in the car. Now repeat the last step adding the same amount that was removed as we did before. Then start the car, shift gears again,

[00:05:00] and top up fluid if necessary. Most cars need to be idling for the gauge reading to be accurate, but check your manual to be sure. Also, make sure your car is on a flat or even surface to avoid false gauge reading. So here’s what I learned. When you change your fluid, you really only get about 50% of the old fluid because the rest gets trapped in the complex maze that is your transmission. Number two, be sure to use the exact spec fluid for your transmission found in your manual.

[00:05:30] or you can cause premature wear. Third, having a drain plug is necessary to complete our compromise between a simple change and our DIY toilet flush as we did in this video. And finally, if you decide to go to a professional, understand the difference between a change and a flush. Make sure your mechanic knows you know the difference between the two services, how many liters your tranny holds, if he changes the filter and of course, if this is included in the price. For more auto repair how-to videos, visit autoblog.com/wrenched.

[00:06:00] I’m Larry Kosilla from ammonyc.com. As always, thanks for watching.

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