Transmission fluid plays a vital role in keeping your car running efficiently. As the vehicle runs, the fluid lubricates the transmission box components to reduce wear and tear. On occasion however, your car can experience a transmission or gearbox oil leak, which requires immediate attention.
This guide will show you how to find a transmission fluid leak and what action you need to take to fix it. If you require replacement fluid for your car, check out our range of automatic and manual transmission fluids to get your car running efficiently again.
1. Spot The Leak
To begin fixing a transmission fluid leak, you first need to locate it. This fluid will often be red in colour, but can also be dark brown if the fluid is old. The colour is different to help you tell the difference between transmission fluid and motor oil, which is typically amber-coloured.
If you are struggling to find the leak, place a bright piece of disposable material underneath the car, such as cardboard, to try and identify where the fluid is coming from.
2. Find The Source
Once you have confirmed it is a transmission fluid leak, it’s time to find the source. Medium-to-larger leaks can be easier to trace back, but smaller leaks are much harder to locate. When this is the case, clean the underside of your car and take it for a drive.
Place another piece of material underneath the car and look for the leak. The short drive aims to trigger the leak again and help identify its source more easily.
From here, it’s time to decide whether to fix the leak yourself or take the car to a garage. If you feel confident in fixing the issue, continue on for how to do that.
3. Drain The Transmission Fluid
Tackling a transmission leak will require the following tools:
- Jack and jackstand
- Wrench set
- Large pan
- Rubber hose
- Replacement transmission fluid (see your vehicle manual for which you will need)
Start by draining the fluid from the reservoir. This will require either removing the drain plug or unbolting the transmission pan, depending on your vehicle.
If your car has a drain plug:
- Jack up the car and support with a jackstand
- Place cardboard and a large pan underneath
- Release the drain plug
If your car does not have a drain plug:
- Jack up the car and locate the transmission pan (check your vehicle manual to find its position underneath)
- Place cardboard and container underneath the transmission pan
- Gently unscrew one pan bolts, letting the fluid drain. Gradually unscrew the other bolt
- As the pressure lowers, remove any remaining bolts and lower the pan
- Tip any remaining fluid into your container
4. Repair The Leak Source
The source of the transmission leak can be one of several. We have outlined the most common leak sources for you to identify:
Damaged Transmission Pan
Whilst you are draining the transmission fluid, check for any damage to the pan. A hole or gap may have formed due to wear and tear.
This will require ordering a new transmission pan and screwing it in place of the old one.
Faulty Transmission Pan Gasket
The transmission pan gasket is a small length of rubber that rests between the pan and its housing. Any gaps in the gasket will leak fluid, so if you identify this as the source, replace it as soon as possible.
Ruptured Transmission Seal
If the transmission seal is torn, this can leak fluid between the transmission case and the torque converter.
This damage usually occurs over time as the seals build pressure.
Worn-Down Plugs and Bolts
Sometimes, the source of a transmission leak can be due to the plug or bolts on the pan.
If these are worn-down, replacing them can help plug those leaks back up.
5. Replace The Transmission Fluid
Now that the leak is fixed, replacing the transmission fluid is the final step. Always check your vehicle manual to ensure you are using the correct fluid for your car.
Lower the vehicle from the jack and fill the transmission via a funnel for a cleaner process. Consult the fluid level to make sure you aren’t overfilling.
Once everything is sealed up, go for a quick test drive to check for any further leaks. If none appear, you are good to go.
Monitoring your transmission fluid should be a regular check to keep your car running smoothly. Check out our guide on how to assess your car’s transmission fluid and which replacement you may need.