DIY

How to Fix a Transmission Leak

Reading Time: 5 minutes

Special fluids are used to keep your car’s components cool, and at times lubricated. These fluids should be inspected periodically, but because of advanced formulation they don’t typically need to be changed out often. This is why the likes of oil, coolant, brake fluid, and transmission fluid typically are forgotten about till their systems run dry. The transmission is a complex system made up of dozens of moving parts sometimes controlled electronically. Transmission fluid is essential to keep the parts lubricated and is also used to activate clutches when pressurized. Forgetting about the periodic maintenance of the transmission fluid is only one way of drying out the transmission. Even though the system is sealed, leaks can form from damage. In the event that your car has a transmission leak, you can follow these steps to fix your leaking transmission.

The transmission is a complex system made up of moving parts working together so that the engine can efficiently transfer power to the wheels.

Locate the leak

(Transmission fluid pan, front main seal of the transmission, axle seal, or where the CV(constant-velocity) axle meets the transmission)

Locating the transmission fluid leak will give you an idea of how technical patching it will be. If your leak is coming from the front main seal of the transmission, it is a good idea to bring your car to a transmission shop immediately. Proper tools, and safety will be needed because the transmission will need to be lowered from your car. A transmission is extremely heavy and can potentially hurt you if mishandled. If the transmission fluid pan or axle seal is the cause of the leak, it is simple to fix.

Transmission fluid pan leak

Barring any physical damage to the transmission fluid pan, the usual cause of the leak is with the gasket.

1. Drain the remaining transmission fluid from the pan. GM vehicles typically don’t have drain plugs underneath the car for the transmission fluid. You’ll be required to drop the transmission fluid pan before draining it so be aware you will be spilling transmission fluid.

2. Undo all the bolts of the pan. Be prepared with a bucket to start catching the transmission fluid if you have not drained the transmission fluid pan. Pry open one side only to help the contents drain into the bucket. BE CAUTIOUS not to get any on your skin or into organic materials such as houseplants or grass. DO NOT dispose into the gutter or a drain. Check with your local authorities for proper recycling of your transmission fluid.

3. Pull pan off of the car.

4. Remove the old gasket, and clean the edges with a wet sponge and paper towels. 

If the transmission fluid you drained is not reusable, it’s best to refill with fresh fluids.

5. Place the new gasket on top of the clean pan making sure that it fits. Some gaskets may need liquid gaskets or room temperature vulcanizing (RTV) silicone gaskets. Read the manual which came with the replacement gasket to avoid future leaks.

6. Reattach the transmission fluid pan making sure the bolts are torqued to spec. For torque specifications, check the vehicle owner’s manual. If there are no torque specifications make sure not to over tighten the bolts to avoid dethreading and damaging the replacement gasket.

7. Refill your transmission fluid through the reservoir in the engine bay. If the transmission fluid you drained is still good, you may reuse it. In the case of older transmission fluids, it is suggested that you refill the transmission with fresh fluids—Automatic transmission fluid (ATF) for cars with automatic transmissions and manual transmission fluid (MTF) for cars with manual transmission. Other transmissions like a continuously variable transmission (CVT) or a dual clutch transmission have their respective fluids. Check your owner’s manual for the specific fluid you need to use for your transmission.

8. Start your car and let it run for five to ten minutes. Check for leaks in the area which was just repaired. Also check the ground where the car is parked for transmission fluid residue. If there is still a leak, repeat the process or bring your vehicle to a transmission shop for more thorough inspection.

Axle seal leak

Much like the transmission fluid pan, the axle seal typically leaks when damaged or from aging gaskets. This requires you to remove the CV axle and replace the ring gasket.

  1. Lift the front of your car with jack stands and secure them into place.
  2. Remove the front tire where the axle seal is leaking.
  3. Remove the tie rod.
  4. Remove the nut which secures the axle shaft.
  5. Remove the nuts and bolts holding the wheel hub to the strut assembly.
  6. Using a pry bar, pull the inner axle free.
  7. Pull out the CV axle assembly to expose the axle seal.
  8. You can use a seal puller or a pick to pull out the seal.
  9. Place the new seal/gasket into the hole where the old seal came off of.
  10. Use a socket extension to tap the seal into place.
  11. Insert your CV axle assembly from where it was removed and hammer it till secured.
  12. Reassemble all the components that were removed.
  13. Start your car and run for five to ten minutes checking for leaks.
A transmission is extremely heavy and can potentially hurt you if mishandled. If you lack proper equipment to fix it, seek professional help.

A healthy transmission lets your engine efficiently transfer the power it generates to the wheels. Better performance and less stress to the engine will give you a more enjoyable driving experience. During your periodic maintenance, ask your trusted mechanic or dealership to do a quick visual check underneath your car for transmission leaks. This quick check can avoid running your transmission dry which will lead to destroying the whole system. The cost of replacing your car’s transmission is sometimes the same price as purchasing a new car.

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CarParts.com

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In the Garage with CarParts.com is an online blog dedicated to bringing DIYers and devoted car enthusiasts up to date with topical automotive news and lifestyle content. Our writers live and breathe automotive, taking the guess work out of car repairs with how-to content that helps owners get back on the road and keep driving.