What to Do If Your Transmission Is Leaking?by Michael O. Smathers
If you've driven your car away from your garage or parking spot and noticed a puddle of fluid under it, you could have a transmission leak. Without transmission fluid, your gears have nothing to lubricate them against the effects of friction. Therefore, they become stripped and cannot create motion. In addition, transmission fluid provides the hydraulic force necessary to shift gears. Repairing a leak as soon as you discover it could save you the expense of buying a new transmission — potentially thousands of dollars.
Diagnose the Leak
Seeing a puddle of reddish-brown fluid under your car when you move away is one sign of a leaky transmission, but there are several other signs. Low transmission fluid can cause gears to be unresponsive or to slip when shifting. Also, if you hear the sound of gears grinding, it's a sign that you need to check your transmission fluid levels. According to California State University Automotive, you can also determine the state of your transmission fluid by its color: as fluid ages, it changes color from red to brownish-red or dark pink.
Locate the Leak
To locate the leak, elevate your car with a jack and look under the middle toward the front. Repairing the leak will require you to take the car to a mechanic. Leaks toward the front of the vehicle indicate a bad seal or gasket. Fluid typically leaks from either a seal or from the fluid pan. If fluid is leaking from the front seal where the transmission attaches to the torque converter, your mechanic will have to remove the transmission and add a replacement seal.
DIY Transmission Repair
If you have a minor leak, you can use a commercial transmission sealer until you can get the car to a mechanic. Sealers penetrate worn and shrunken gaskets and seals, causing them to swell and form a seal against leaks. It is applied in the same manner as standard transmission fluid (i.e, poured in the transmission receptacle under the hood.) Only use sealer as a one-time solution.
Add Transmission Fluid
If you've already taken steps to repair the leak, you need to replace the fluid you lost. Use a funnel, paper towel and the transmission fluid that is intended for your vehicle's make and model. Start the car and let the engine warm up if your vehicle requires you to do this. Remove the transmission fluid dipstick near the rear of the engine. Its handle may also be marked "Trans Fluid" or similar. Clean the dipstick; any solid debris can damage the transmission. Place the dipstick and take a "Warm" reading. Use a long funnel to add fluid to the proper amount.
Even after repairing a transmission leak and replacing lost fluid, you need to have it checked regularly to ensure problems do not occur. Regularly check your transmission fluid levels and change it every 30,000 miles.