How To Flush Your Automatic Transmission At Home With Basic Tools

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    If you have an older vehicle that you care for on your own then you know that saving some money and doing the work right will make your car last longer and reduce the chance of a big expense in the end.

    I would not suggest that you perform this work on a car that is still under drive train warranty because your dealer can do this for you but if you have an older car that is past its warranty period and you haven’t changed the transmission oil and filter you can benefit from using this Do It Yourself Method that many mechanics suggest.

    The first thing you need to understand is that Automatic Transmissions basically run on the hydrolic fluid that is used for transferring the torque or output strength of the engine to the transmission and eventually into the wheels of your vehicle. In addition to the Torque Converter which can hold many quarts of fluid the internal valves and lines of the transmission and the transmission cooler which may be separate or part of your radiator will hold a lot of fluid that you just can not drain by pulling your transmission pan and filter out.

    Using Your Transmission’s Pump To Flush Your System

    Transmissions have pumps that are built into the front end of the transmission. They make sure that the transmission has plenty of fluid so it is not running dry and it pumps that fluid up to your radiator to cool it to reduce the temperature of the fluid.

    To flush your transmission you will first want to go through the process of removing the pan and filter. Most vehicles have transmission filters however some may only have a screen that is not serviceable without removing the transmission. If you have a filter then replace it and you will need to replace the gasket for the transmission pan.

    Make sure you clean the surfaces of the transmission pan and the area where it mounts on the transmission housing. Only use chemicals that are safe for your transmission when cleaning. Normally a Non Chlorinated Brake Cleaner in a Spray Can is your best bet as the friction parts, bands and disks, inside the transmission are similar to that of your brakes. Do not spray the internal parts of the transmission use a small amount on a lint free rag to clean the transmission surfaces. Never use Carburetor Cleaner or other degreasers. Replace filter and the pan using a new gasket and torquing with an inch pound torque wrench to the proper spec.

    Now you are ready to flush your transmission. The first thing you will need is a diagram of your transmission fluid lines. If you can not find one you can do a quick test and what you are looking for is the line that forces fluid out of the transmission and up to the radiator. Install a clear plastic tube to the fitting on the transmission and run it into an empty and clean bucket. Turn the car on for a few seconds and fluid should run out. You may need to put the vehicle in gear or in neutral to start the flow of fluid but it can pump pretty fast so keep your eyes on it and just find the line that is the pressure line.

    Now you are ready to start adding fluid to the transmission while your system drains from your pressure line. It is best to have a helper while doing this but you can do this on your own if you have a funnel set up and you can see the fluid level as it drains. Have your bottles open and ready to go and if there is a problem just turn the vehicle off and catch up. You should not cause any major damage because your drive wheels are not engaged and the friction parts in the transmission are not active but you do not! want your transmission to run dry while you are doing this. Additionally running your transmission on low fluid can cause foaming of the fluid just like a washing machine with way too much soap. You want to add fluid at the same rate that it is coming out and that is pretty fast.

    Once you have forced about 6 quarts of fluid through your system and the fluid that is exiting the clear tube has changed color to a new fluid look you can stop the engine and replace the fluid line.

    I suggest you let the vehicle rest until it is cool or at least 15 minutes and then check the fluid level with the dip stick. If you have a cold level line you should make sure that there is at least some fluid on the dip stick and make sure that it is not above the cold fluid line. Then start the vehicle and test the fluid level as it is running. Your vehicle may have other methods of testing the fluid level so follow your owners manual or ask your dealer before you attempt this procedure.

    Finally top off the fluid to the correct level. If the fluid level is too high then you will have to remove some of the fluid from the system and you already know how to do this.

    A half or even a quarter of a quart of fluid can change the level on your dipstick pretty quick especially on small vehicles.

    Final Note

    As you can see I did caution you about a lot of things while performing this service. The best situation is if you have a helper that can either start the vehicle and turn it off as needed or pour the fluid.

    The most important thing is to not run the transmission dry so keep adding quarts of fluid as it drains and if you fall behind just stop.

    Be careful while you are working especially if you need to take the vehicle out of park and put it in neutral to get the pump working. Block the wheels with chocks along with applying the emergency brake and stand out of the way just in case the car slips into gear by accident. Just be careful.

    When the work is done your transmission will run better and your car will perform better.


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