Replacing the Transmission Seal for the Transfer Case Input Shaft on a 1st gen Tacoma (or 3rd gen 4Runner)

The transfer case on a 1st gen Tacoma is generally known to be a very reliable part - often lasting 300-500K miles. However, it is very common to develop a leak in the seal that keeps - or is supposed to keep - the space between the transmission and transfer case dry, resulting in a reasonably constant wet spot between the two components, and often a drop of oil on the transfer case skid plate.

If you have a 1st gen Tacoma, you're likely familiar with this leak.

The seal in question housed in the transmission, and seals around the input shaft of the transfer case, where it connects to the transmission.

This guide will walk through how to fix this issue, including the parts and tools needed to access the old seal and replace it with a new one. And, while the specifics apply to a 1st gen Tacoma, the process is generally the same for any vehicle.

Parts

• Toyota OEM Input shaft seal for transfer adapter (90311-40007) - this is the only part necessary for this job, though you may consider picking up two of them, just in case you run into issues when fitting the seal into the transmission, or if you accidentally tweak it when reinstalling the transfer case.

The only part you need.

Tools

While several tools are needed to remove the transfer case and access this seal, there aren't many tools needed for replacing the actual seal:

• OTC 4579 Slide Hammer/Puller - used to remove the seal from the transmission, a slide hammer allows you to securely grab the seal without risking damage to the race. You can likely get the seal removed without this tool, but slide hammers come in handy frequently, so treat yourself to the convenience.
• A hammer - just a normal hammer, used to tap the new seal into place
• A flat piece of wood, approximately 1" x 3" x 0.5" - just a small piece of wood that will span the diameter of the new seal, and which you'll tap on with the hammer to seat the seal into the race.

The only tools you'll need.

Supplies

You'll only need a couple of supplies for this job:

1. Red-n-Tacky Grease - used to lubricate the ouside surface of the new seal, and the race in which it sits in the transfer case.
2. The appropriate fluid to refill any that has leaked from transmission as a result of the original leaking seal:
   1. Manual Transmission Tacoma (or 4Runner)
      • Lucas 80W-90 Gear Oil or MT-90 Oil.
      • A Fluid Pump for Quart Bottles
   2. Automatic Transmission
      1. Toyota Genuine ATF Transmission Fluid Dexron III (00718-ATF00), or another Dexron III ATF
      2. A Long Neck Plastic Funnel that reaches the dipstick hole for the transmission.
3. Shop Towels - as necessary.

Doing the Job

Replacing the seal is pretty simple. However, it requires removal - and eventual reinstallation - of the transfer case. This process isn't overly difficult either but can be time consuming and finicky in places.

Removing the Transfer Case

In order to replace this seal, you need to remove - and reinstall - the transfer case. That procedure is covered in the following guide.

Note: if you are reinstalling your current transfer case, there is no need to drain the oil out of it prior to removal, so start at the section entitled "Disconnecting and Removing the Front Drive Shaft." After completing the section entitled "Removing the Transfer Case," continue with the steps in this guide.

Removing the Input Shaft Seal

Removing the seal can be done a number of different ways, but I've found it to be much easier, faster, and entail less risk of marring the race for the seal, if you use a slide hammer with the appropriate attachments.

1. Assemble internal 3-jaw puller for the slide hammer and install it onto the end of the slide hammer so that the jaws are narrow enough to fit into the center of the old seal.

   

2. Insert the jaws through the center of the old seal.

   

3. Screw the slide hammer further into the 3-jaw puller so that the tip of the slide hammer shaft expands the 3-jaw puller just enough to securely grip the installed seal. Note: ensure that the puller is not expanded so much that it will scratch the surface of the race containing the seal.

   

4. Use the slide hammer to pull the seal out of the transmission.

   

Preparing the New Input Shaft Seal and Mating Surfaces

After removing the old seal, all that's necessary is a bit of cleanup, preparation of the new seal, and installation of the seal into the transmission.

1. Using shop rags, clean up any oil or dirt that is evident on the transmission, especially in/around the race in which the new seal is to be inserted.

   

2. Compare the old seal to the new seal to confirm that they are identical.

   

3. Spread a bit of Red-N-Tacky grease in the race where the new seal will be installed. Note: you don't need a ton of grease here, just enough to make it easier for the new seal to slip in.
4. Spread a bit of Red-N-Tacky grease on the external surface of the new seal that will slide into the race. Note 1: Be careful not to disturb the factory installed grease on the internal surface of the new seal. Note 2: you don't need a ton of grease here, just enough to make it easier for the new seal to slip in.

   

5. Spread a bit of Red-N-Tacky grease onto the input shaft of the transfer case, including the shoulder closest to the transfer case itself, which is where the seal ultimately rides.  Note: you don't need a ton of grease here, just enough to make it easier for input shaft to slip into the new seal.

   

Installing the New Input Shaft Seal

1. Place the new input shaft seal in place against the transmission. Ensure that it is centered on the race so it will go in straight.
2. Place a small piece of wood over the input shaft seal and using a hammer, tap around the diameter of the seal, seating it into position. Note: go slowly here. The seal is in position when the surface of the seal is flush with the flat surface surrounding the race. This is the location where the wood will no longer allow the seal to be tapped further into the race.

   

That's it! (For installing the new input shaft seal.) All that remains is to reinstall the transfer case.

Installing the Transfer Case

Installing the transfer case  is covered in the following guide.

Note: Begin with the section entitled "Installing the Transfer Case." Pay special attention to alignment of the transfer case input shaft with the new seal that was installed into the transmission. The easiest way to wreck the seal is to drag the input shaft over the interior surface of the seal, ripping it.

Replacing any Lost Fluids

As the leaking seal allowed oil from the transmission to leak out, that oil (MT) or ATF (AT) needs to be replaced.

Manual Transmission

1. Remove the 24mm fill plug on the manual transmission and fill the transmission with oil until oil begins to seep out of the fill hole.
2. Secure the 24mm fill plug with a new crush washer and torque to 27 ft-lbs.

Automatic Transmission

1. Remove the dip stick from the automatic transmission.
2. Insert a Long Neck Plastic Funnel into the dip stick tube.
3. Fill the automatic transmission with ATF until full.
4. Replace the dip stick.

Congratulations, you're done! Drive the truck - to make sure that everything is OK. As you removed the transfer case, test out 2WD, 4-Hi and 4-Lo to ensure that you reconnected all of the sensors correctly. If you have a rear e-locker, try it out too in order to make sure that the various dash lights illuminate (and things like ABS - again, if so equipped - are disabled).