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How To Change Your Transmission Fluid

Abby Wingett | 28th July 2022 | 11 minutes to read

As you jump behind the wheel of your car and select drive, most times you won’t give a second thought to the complexities and intricacies of your automatic transmission. With 95% of new cars now sold utilising an automatic transmission the technology and efficiency has vastly improved with this increased usage. This means you need to remain vigilant of correct servicing of your transmission as the many shift valves, gearsets and clutches all need the lubrication and protection of transmission fluid.

Answering a few of the common questions relating to automatic transmission fluid the following article explains some of ins and outs about your transmission system.

  1. How often should I change my transmission fluid?
  2. Why is it important to change your transmission fluid?
  3. 5 signs you need to change your car’s transmission fluid
  4. What if my automatic transmission is a sealed ‘lifetime’ unit?
  5. Benefits of changing your transmission fluid
  6. What you will need:
  7. Steps to changing your transmission fluid

How often should I change my transmission fluid?

This question is both vehicle specific and usage specific. Your vehicle service manual will indicate how often this should be changed along with the specific transmission fluid the unit takes. Usage can vary significantly, and any manufacturers service interval will be based on standard day to day driving. Hard driving and towing are 2 areas that will see excessive temperatures and load placed on your transmission so more frequent fluid changes would be advisable.

Most car manufacturers recommend changing your transmission fluid every couple of years with a service interval between 50,000km to 100,000km. Between these intervals it is important to occasionally check your transmission fluid levels to avoid issues that come from low transmission fluid.

Why is it important to change your transmission fluid?

With any fluids in your vehicle, it is important to regularly change these to ensure the lubrication and protective qualities remain. This is especially true of automatic transmission fluid as the tolerances that these unit operate within mean any degradation of fluid limits the effectiveness and efficiency of the driveline power transfer.

Deterioration of automatic transmission fluid over time may contribute to loss of lubrication and cooling capacity and when this occurs gear selection can become sluggish or strained and metal on metal contact may occur. If you notice any odd symptoms when changing gears, or a grinding noise coming from the transmission it is important to check what is going on, and even if it is before your regular transmission change it might be worth doing a transmission fluid change to limit damage.

5 signs you need to change your vehicle’s transmission fluid

  • Gear slippage or difficulty changing gears– this usually will happen when your vehicles transmission fluid is dirty, or you have low fluid levels. When changing gears your transmission should smoothly engage gears with minimal hesitation. If your transmission is slipping this means, there is not enough hydraulic pressure for your gears to remain in place.
  • Grinding noise – Insufficient transmission fluid coupled with possibly worn linkages or misaligned components may contribute to grinding in the transmission.
  • Engine light illuminating on the dash – if the engine light appears on the dash this is an indication that there is an issue under the bonnet. Engine light can come on for a variety of reason however this can come on if there is an issue with the sensor within your transmission.
  • Vehicle surges – this can happen if contaminants or gunk in your transmission stop or slow down the flow of the transmission fluid. This can cause the car to randomly surge forward.
  • Transmission smells – If you start to notice an unfriendly smell coming for your transmission this is sign that your transmission fluid needs to be top up, changed or your transmission has burnt fluid. If you need to check the fluid level, you just need to check the dipstick when you are on flat ground. If there is burnt fluid this means, there is something wrong with your transmission and needs to be checked properly.

What if my automatic transmission is a sealed ‘lifetime’ unit?

With many manufacturers looking to cut initial manufacturing costs as well as ongoing service costs you may find your automatic transmission is classed as a ‘lifetime’ sealed unit. This will mean that it does not need servicing and comes without a dipstick to check fluid level. Whilst this may seem to be one less thing to worry about it pays to understand what ‘lifetime’ means from your manufacturer’s perspective.

If your automatic transmission was to fail at any point the manufacturer may specify that this was the ‘lifetime’ of that unit thereby leaving you out of pocket and with a broken vehicle. Always consult a reputable mechanic on the potential of failure with your particular transmission and understand that servicing at points may be required.

Benefits of changing your transmission fluid

  • Smooth gear shifting
  • Enhance engine performance function
  • Minimises the chances of transmission issues
  • Reduces the temperatures of the transmission
  • Better fuel economy

How to change your transmission fluid

What you will need:

Steps to changing your transmission fluid

Step 1: Saftey first

When doing a transmission change your fluid will drain better at operating temperature. So let the car idle for a few minutes before you begin to change the fluid.

Ensure your vehicle is turned off and in park mode/ in gear with the hand brake engaged. Place your gloves on, and you are ready to get started.

Raise up your vehicle safely on flat ground, using your jack, lift the vehicle up and place stands under the vehicle both front and rear.

Step 2: Visually inspect the transmission and locate the drain plug

Once the vehicle is up on stands visually check the transmission to ensure the transmission is not leaking. Be careful as the transmission may be hot.

Locate the drain plug, the drain plug location can vary depending on which vehicle. Some vehicles may require you to take the whole oil pan off in order to drain the transmission fluid and others require you to suction the fluid out from where you top up the trans fluid.

To find out where your drain plug is located and what the correct procedure is for your vehicle check your vehicle manual.

Step 3: Remove the drain plug or transmission pan

Once you have located your drain plug place your drain pan under it so it can capture the oil when you release the drain plug.

Using the correct size spanner or ratchet and socket remove the drain plug, however, remember the fluid may still be hot so be careful when remove the drain plug.

If no drain plug exists, you will need to remove the transmission pan to drain the fluid. Starting with the rearward bolts, work your way forward to enable the fluid to drain from the rear of the pan. Leaving the front few bolts in place will allow for the majority of fluid to drain from the rear. This can get messy so have a large drain pan and adequate rags to catch all the fluid.

Once the fluid has finished draining then remove the remainder of the bolts with one hand whilst holding the pan with the other.

Inspect both the drain pan and fluid to ensure no excessive amounts of metal are in the fluid. If metal fragments exist there may be damage to the transmission, and this will need to be examined properly.

remove the drain plug or transmission pan

Step 4: Remove the old pan gasket and transmission filter and clean the oil pan

With the fluid drained and the transmission pan off you now need to remove both the old filter and the gasket that was between the transmission body and the pan.

If the gasket is a paper or cork construction, you will need to carefully scrape both mating surfaces with a plastic scraper until clean. Don’t using any sharp objects or metal scrapers to remove the gasket as it can cause damage to the mating surface and cause leaks. If the gasket is rubber these usually can be removed in one piece. Clean all surfaces to ensure solid contact when refitting.

To remove the transmission filter these can be either be held in place with a locating bolt or just a press fit. This should not require undue force to remove.

You will also need to clean the oil pan so using a lint free cloth and ample amounts of brake cleaner ensure the drain pan is spotless prior to refitting.

Step 5: Fitting the new transmission gasket and filter

The new filter should be easily reattached either as a press fit or secured with the locating bolt. Make sure the filter is secure before looking to reattach the transmission pan and gasket.

When replacing the gasket, you may require a gasket sealant. Place the gasket around the edge of the oil pain before re-attaching the oil pan. Once the gasket is in place you can re-attach the pan to your vehicle, tightening each bolt using a spanner or socket and ratchet it is in place. Once they are all tight using a torque wrench to tighten to the specific tension for your vehicle as per your vehicle manual.

Step 6: Clean and place the drain plug back in

Clean your drain plug with a rag, place a washer on the plug and put a small amount of thread sealant around the thread of drain plug.

Place the plug back in place and tighten by hand until firm, then using a torque wrench tighten to the torque specification for your vehicle.

Step 7: Fill your vehicles transmission up with new fluid

As a close estimate look to see how much used transmission fluid you drained. This will give an indication of how much you need to refill and using the new fluid fill up your transmission with that required amount. The vehicle manual may advise how much total transmission fluid your vehicle takes but a service will only change 40-50% of the fluid in your transmission. This is due to the volume of fluid trapped within the transmission unit that will not drain.

Depending on your vehicle will depend on how you can refill your transmission, it can be either done by a plug on the side of the transmission using a transfer pump or transfer syringe to push the fluid in , or through the dipstick using funnel or again can use a transfer pump to fill up your transmission.

Once you have added the correct amount of specified transmission fluid check the dipstick to ensure the fluid is registering at or above the cold line on the dipstick.

Step 8: Final checks

Jack up the vehicle again enough to remove the jack stands from under the vehicle. Once the vehicle is back on the ground start the vehicle up, and let it run for a little while, then turn the vehicle off and check for any leaks around the transmission. If there are no leaks again start your vehicle up and placing your foot on the brake run through the gears in your vehicle allowing the new fluid to flow through the transmission.

Place the vehicle in park mode and let the car idle whilst you check the dipstick ensuring that the dipstick is at the correct line for when your engine is hot. If correct, place the dipstick back in and turn the vehicle off.

As you can see changing your transmission filters and transmission fluid is quite a simple job, with the correct tools and set up. We encourage you all to give it a go. However, if you prefer to get it done by a professional, check out our Repco authorise services or your local repair shops will be able to assist you in installing new transmission filter and transmission fluid.

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