When your car is leaking transmission fluid, there are several places to check for faulty parts. The leak could be in the transmission pan, torque converter, pan gasket, fluid lines, or oil seals. Placing a traceable, glowing dye in your car’s transmission fluid may be the easiest way to troubleshoot the location of the problem. When you drive the vehicle for a short time, the fluid containing the dye will flow through the system and the location of the leak will begin to glow.

If you determine that the leak is caused by a faulty oil seal, you will need to locate the defective part. It takes patience to access a broken seal, as it often requires disassembling parts of your vehicle to reach it. Your next step will be to decide if you want to replace the transmission oil seal yourself or hire a mechanic to do the work for you. While the job does take some time, it may be worth the effort to save the expense of a professional repair.

Cost to Professionally Replace Transmission Oil Seals

Transmission oil seals are generally manufactured of synthetic rubber, and can receive damage from a number of causes. Sometimes they simply become warped or worn out from regular use. They are consistently exposed to heat, which can crack and fray them over time. Seals commonly break in the input and output shafts.

The price to have a mechanic replace the transmission oil seals on your vehicle can range anywhere from $200 to $600 or more, depending on which seal must be replaced and how much time and effort is required to get to it. The expense of replacing transmission oil seals yourself is surprisingly low, especially if you already own or can borrow the necessary tools. Transmission seals cost around $5 each, so you could easily do the job on your own for less than $20 and a few hours of time.

How to Replace Transmission Oil Seals

As with any car repair, it’s a good idea to begin by checking the owner’s manual for safety guidelines and vehicle maintenance recommendations.

1. 1.     Gather the necessary tools and parts to complete the repair. You can find the correct type of seal for your vehicle by checking the owner’s manual, looking online, or talking with someone in the customer service department at your local automotive store. In addition to the correct replacement seal, you will need the following:

• safety equipment such as steel-toed shoes, latex gloves, safety glasses, and a portable light source
• floor jack
• jack stands
• wheel blocks (metal wheel chocks, bricks, wooden wedges, etc.)
• container to catch transmission fluids
• shop towel
• set of wrenches
• hammer
• seal remover or flathead screwdriver
• transmission fluid

1. 2.     Experts recommend that you wear protective glasses any time you do vehicle maintenance. Other safety gear, such as gloves or steel-toed shoes, may also be necessary, depending on the type of repair you are working on. It may be helpful to have an alternative light source for working in and under your vehicle.

1. 3.     Prepare and jack up the vehicle. Always park your vehicle on level ground before you jack it up to prevent it from rolling while you are working on it. Put the vehicle in park and engage the parking brake, then place wheel blocks at the end of the car that is not being raised. Position the jack in the appropriate place for your vehicle. You can find this information in your owner’s manual or by contacting the service department at your automotive dealer. Use the jack to lift the vehicle and put the jack stands in place, then lower the vehicle onto the stands. Wiggle the vehicle a little to make sure it rests securely on the stands.

1. 4.     Remove the vehicle’s parts to access the faulty seal. Once you’ve located the leak, follow the diagrams in your owner’s manual to determine which parts must be removed and how to take them out in order to access the seal. Remove the bolts and driveshaft universal c-clamps at the pinion. Place a container below the tail shaft to catch any leaking transmission fluid, then remove the driveshaft from the transmission.

1. 5.     Replace the damaged seal. Use a seal remover or flathead screwdriver to carefully remove the broken oil seal. Be very careful not to scratch the transmission or you will have to replace the tail shaft to prevent further leakage. Put the new seal in place, gently tapping the edges in with a hammer, if necessary, to get it all the way in. Applying a lubricant to the seal before installing it may help it to go in more easily.

1. 6.     Replace the automotive parts in the correct order. Push the driveshaft back into place, then reposition and tighten the c-clamps. Replace and tighten the bolts.

1. 7.     Refill the transmission fluid. If the fluid you drained off earlier appears clean, you can reuse it to refill the transmission. If it is dark, then you will need to dispose of it and refill the transmission with new fluid. Make sure you have enough fluid on hand plus a little extra to refill it accurately. Turn on your engine and shift through all the gears to make sure the fluid is evenly distributed.

1. 8.     Clean up your work area by removing tools and extra parts from your work area. Wipe up any spills and remove the drain pan. Replace the jack, remove the stands, and lower the vehicle until it rests on the ground. Remove the jack and wheel blocks.

Once you’ve completed all the steps for replacing transmission oil seals, you may want to take a short test drive to make sure all the leaks have been repaired. When you return, you should see no sign of transmission fluid.

Replacing transmission oil seals takes time and patience, but it can save the cost of hiring a mechanic to do the work for you. Always use caution and the correct tools and parts to prevent injury to yourself or your vehicle.