To watch this repair being done, please watch the full video below:
Video Source: http://www.1aauto.com/content/video/how-to-replace-the-rear-transfer-case-seal-on-a-full-size-chevy-blazer-chevy-truck-gmc-jimmy-or-gmc-truck
3/8-1/2 inch Wrench
Hammer or Rubber Mallet
Flat Blade Screwdriver
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Step 1: Disconnect the Driveshaft From the Rear-end of the Vehicle
Remove driveshaft by removing four bolts at the rear and using a large screwdriver to pry it out. This is easiest with vehicle in gear. Use a screwdriver to mark one side of driveshaft and rear-end so they can be lined up when reinstalling.
Step 2: Pull the Front of the Driveshaft Out of the Transmission
With a catch pan underneath, pull the front of the driveshaft out of the transmission. This is important because on some transmissions, when you pull the front of the driveshaft out, you will lose fluid.
Step 3: Remove Old Transfer Case Tailshaft Seal and Wipe Down Seat
Remove transfer case tailshaft seal using a flat blade screwdriver and hammer to pry it out. Be careful to not damage the transfer case tailshaft. Wipe out the transfer case seal seat with paper towels.
Step 4: Install New Transfer Case Seal Into Place
Gently tap new transfer case seal replacement way into place using hammer or rubber mallet. Place a 2x4 with a 1-1 1/2 inch diameter hole cut out over the transfer case seal and use hammer on wood to push the seal all the way in. This makeshift "tool" will distribute the hammer's force more evenly over the tailshaft seal.
Step 5: Reinstall Front of Driveshaft Into Transmission
Insert front of driveshaft into transmission making sure that mark on rear of driveshaft is on the same side as mark on the rear-end. You may need to use a rubber mallet to get the driveshaft past a certain point, after that it should slide in.
Step 6: Reinstall Driveshaft Into Rear-end
Line up and install driveshaft into rear-end. Re-install the four bolts and torque them to 20 ft-lb.
Step 7: Start Vehicle Up and Refill Transmission Fluid According to Manufacturer's Guidelines
Start the vehicle up and get it warmed up. Then refill the transmission fluid according to manufacturer's guidelines to make sure it's at the proper level.
That is how to replace a transfer case tailshaft seal on full-size Chevy Blazer, Chevy Truck, GMC Jimmy Or GMC Truck models.