NP 231 Jeep Transfer case rear seal replacement.
The stock Jeep transfer case uses a slip yoke at the rear of the transfer case. As the drive shaft slides in and out of the case the seal wears away. This effect is magnified by running in dirty muddy environments. When the seal wears it allows transfer case fluid to leak and is usually evidenced by an oily mark in the tunnel around the front of the drive shaft.
The seal is simple to change even if finding the correct seal is not. Many national discount parts chains like Autozone have started stocking a seal that looks different and in my experience makes an inferior seal to the stock replacement.
I got my seal from Crown Automotive. It is a duplicate of the stock seal. If your local parts stores don’t have the right one try the Jeep dealer or JCW.
I began by removing the rear drive shaft. I removed the U joint strap bolts using my six point 8mm wrench. I inspected the U joints while I had it in my hand.
After removing the drive shaft form the transfer case, I used a screwdriver and a hammer to fold back part of the metal shell of the seal. I drove the screwdriver between the tail shaft housing and the seal bending the seal out and being careful not to damage the aluminum housing.
Because my transfer case skid plate limited access, I simply crushed the seal until I could grip it with a pair of vise grip pliers and pull it out. If I was working on a Jeep with out a skid plate I would have worked the seal out more before using the vise grips.
With the old seal out of the way, I used a rag to clean up the surface and inspected it for damage. Then, I compared the seal to the opening to make sure it was correct before removing it from the plastic bag.
I set the seal in place and tapped it lightly with a hammer to set it in place. I find it difficult to drive these seals in using just a hammer as they tend to twist. I did not have a seal driver handy so I used a sleeve from my ball joint service kit that fit around the flange. A few taps of the hammer seated the seal squarely in the opening. I then used my hammer to tap around the perimeter of the seal to make sure it seated fully.
I applied a bit of fluid to the slip yoke and slipped it back in place. Then I reinstalled the rear of the shaft and the U joint retaining straps.
If you are not sure how much fluid has leaked out, take time to check the fluid level while you are under there. Simply remove the upper plug in the back of the transfer case and make sure the fluid is level with the hole. If not, add the proper fluid for your transfer case to bring it up.
A quick test drive showed no more leaks. I should be leak free for a few more years of off road use.