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How to Change Transmission or Gearbox Fluid - Step by Step Guide

Technical  ·  January 27, 2022

How to Change Transmission or Gearbox Fluid - Step by Step Guide

Transmission fluid or gearbox oil may be new to your ears, even if you've owned a car for years. It could be that it has been a while since you've last changed it, or worse, you may have never done it ever since. 

The gearbox is a component that is often overlooked, and you will probably continue ignoring it until it starts giving you problems in shifting or engaging. 

It requires regular servicing much like any other car part. This article will guide you step by step on the proper way to change your car's transmission or gearbox fluid.

Why Do You Need to Change Transmission Fluid?

Even though the gearbox operates in a sealed unit with no contaminants, there are several reasons why you need to change the transmission fluid, including:

  1. Old oil – When the gear oil aged from prolonged usage, its viscosity destabilises, leading to inadequate lubrication. Poor lubrication prematurely damages the gearbox.
  2. Leaks – When the transmission system has leaks, it results to low gear oil level and probably contamination. Servicing will be necessary to repair the leakage and replace the contaminated oil.
  3. Contaminants – When foreign fluids find their way into the transfer case or differential components and contaminate the gear oil, this will require replacing of the transmission fluid. A classic example would be when a car gets submerged for long in the water, such as in a flood.

How Do I Know the Gearbox Oil Needs Changing?

When the gear oil starts producing a burning smell and the clutch begins making grinding noises, or the gears start slipping, these are signs that your car has faulty gearbox oil and needs to be changed. 

How Often Should I Change the Transmission Fluid?

How regular or often you should change your transmission fluid depends on the type of oil you use and the model of your car.

Typically, synthetic gearbox oil lasts longer than the mineral gearbox oil. On the other hand, different car manufacturers have various recommendations regarding the frequency of changing gear oil. 

Car owner manuals usually recommend gear fluid servicing after approximately 48,000 kilometres (30,000 miles) or 2 years, whichever comes first.

You’ll need transmission flushing after 80,000-95,000 kilometres (50,000-60,000 miles) or 3 years, whichever comes first. 

However, most vehicles hit up to 129,000 kilometres (80,000 miles) without the need of gear fluid change. 

How Do I Change the Gearbox Transmission Fluid?

You may be wondering if you can change the gearbox oil on your own, right? That’s why you’re on this page.

Yes, changing the gearbox oil is not rocket science. Anyone can do it by following the following simple steps. 

Steps for Changing the Transmission Fluid

  1. Get the recommended gearbox fluid for your car and make sure that you have enough quantity. If your vehicle has a transmission fluid filter, also purchase a replacement filter. For cars without a gearbox-oil drain plug and requires the opening of the whole reservoir pan, you will also need a new oil pan gasket.
  2. Bring your car on a level surface and warm it up such that the transmission is at average operating temperature. Put the gear on parking or neutral for manual vehicles and pull the handbrake. Do not forget to have a container such as a bucket to collect the used gearbox oil.
  3. Most modern vehicles have a drain plug through which you can quickly drain the fluids without opening the pan reservoir. In this case, locate the drain plug and unscrew it to pour out the old oil. This may take up to thirty minutes, so be patient and wait until the last drop. After draining the oil, secure the drain plug back and tighten it firmly. If your vehicle is among the models with transmission oil filters, do not forget to replace the filters before adding new transmission fluid. 
  4. In cars with no drain plugs, you’ll have to unbolt the pan reservoir. Loosen the bolts while holding the pan in place, loosen one side of the container more than the other so that it tilts and allows oil to be collected on the one end. Drain the oil from the lowered corner, being careful not to make a mess. The reservoir holds anywhere between 3 to over 10 quarts depending on the vehicle model and size. 
  5. After draining the oil, unscrew the pan entirely and remove the gasket. Replace the gasket with a new one. Make sure not to scratch or bend the pan's gasket surface. Otherwise, the pan-reservoir won't tightly seal, and you will most probably have leaks.
  6. Remove and replace the old filter with a new one. Clips or bolts hold the filters in place depending on the model. Take careful note of all the O-rings or other seals and fit them as they were before unbolting the parts. If the transmission filter has a long intake neck, gently push the neck into place without unseating the O-ring. 
  7. Inspect the oil pan for any damage. Also, check the type of residue that collects at the bottom after draining the oil. Fine grey clutch dust is a typical residue, but fine metal shaving is a sign of transmission damage. It indicates some parts of the transmission have been grinding and wearing each other out. In some vehicle models, a magnet is fitted at the bottom of the pan to trap the metal shavings.
  8. Clean the oil pan thoroughly with a solvent, removing all the oil. Use a magnet to remove the metal shaving residues. If the reservoir has a trap-magnet, it will have collected all the metal shavings. Clean it to remove all the metal shaving. Do not forget to fix back the magnet after cleaning.
  9. After cleaning the pan, position the new gasket ensuring it aligns with pinpoint accuracy. All the four bolt holes should help you to align the gasket.
  10. Fit back the pan with gasket aligning it properly, ready for bolting. Bolt the pan-reservoir in a crisscross pattern by hand and only use a torque wrench when you are sure all the bolts are well aligned. Bolting by hand prevents the pan or the gasket from being damaged. If you can no longer tighten the bolts manually, you need to use a torque wrench to tighten them to the manufacturer-recommended foot-lbs, ensuring there will be no fluid leaks.
  11. The system is now ready for new transmission oil. Most vehicles have transmission oil refill cup above the gearbox, and you may require a pipe/tube to transfer the transmission-oil. Suspend the container above the refill cup, connect the tubing and siphon to initiate the flow. The refill is usually slow, taking about half an hour to one hour, so a thin tube is ideal. Regularly check the oil level and end the refill when the oil reaches the required volume. 
  12. After closing the refill cap, restart the engine and let it idle for a few minutes. Then change the gear into a different position from "Park" or "Neutral" momentarily and shift back to "Neutral." Recheck the transmission oil for any leak. If you find a leak, immediately seal the hole. Add more transmission oil if it is below the recommended level. If the level is okay, you're good to go. In case you’re not sure about something, consult the experts before you attempt anything.

Transmission Service and Transmission Flush – What’s the Difference? 

Regular transmission or gearbox servicing is important to avoid premature wear and damage to other car parts. Don’t wait for these transmission trouble signs to appear before going for a servicing.

Transmission servicing is a regular car servicing where you change - or have the servicing garage personnel change the gearbox oil or automatic transmission fluid (ATF) of your car and the filter for cars with filters.

For cars with an automatic transmission system, you can check out this article to check the level of transmission fluid. 

Transmission service (also referred to as transmission fluid change) only involves draining of the used fluid in the pan, which is approximately a third of the oil. 

On the other hand, transmission flush is a complete draining of the transmission fluid, including the oil in the torque converter (almost 40% of the total) and the cooler lines. In other words, transmission flush is a more extensive task.

Which Is Better – Transmission Flush or Transmission Fluid Change?

Obviously, a change of 100% of the oil sounds healthier than replacing just a third. 

However, a good number of automatic transmissions, especially those with filters, don't need 100% of the fluid changed. Unlike engine oil, which traps by-products of engine combustion, transmission fluids operate in sealed units where no external product finds its way. 

As a result, the gearbox oil doesn't require frequent changing like the engine oil does. Replacing one-third of the fluid is sufficient. 

The one-third change is similar to topping (replacing oil) your cup of coffee (ATF) to keep it hot and fresh, except that you need to throw out the ATF to make room for the replacement oil. 

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