Tailshaft Tech

The Ocala Jeep Club of Florida

The Tail Shaft Bushing By Ron Tyrie II

The main parts that make up the NP231 are the front case half, planetary set, shift mechanism, front drive chain, main shaft, oil pump, rear case half, rear output housing and the slip yoke housing.

The slip yoke housing’s (tail shaft housing) main function is to contain the drive shaft slip yoke. It performs this function through the usage of a sleeve bushing fitting around the drive shaft slip yoke. If you ever notice a leak coming from the back of your NP231 transfer case the problem is not with the output seal but with the tail shaft bushing. If only the seal is replaced, you will soon notice the leak returning every bit as bad as before. As you can imagine this bushing is a wear intensive component (especially with the addition of a lift kit and oversized tires) and has been known to be the root cause of catastrophic failures. Basically what happens is the bushing wears, the owner does not notice the leak, all the fluid leaks out, the oil pump burns up, bearings fry, and you would be lucky to even salvage the case halves. Even with all of its inherent drawbacks the stock tail shaft configuration is more that sufficient for most drive duties.

Checking the bushing for wear: Ok, so now we have a fluid leak out of the back of our NP231. We suspect that the bushing may be worn, how do we check it? Simple. Grab a firm hold of your rear drive shaft and work it up and down. A tail shaft bushing in good repair will not demonstrate any “play.” If there is play, you can remove the drive shaft (make sure you drain your transfer case fluid first), when that is done go ahead and remove the output seal, it is much easier to do it now. Then, the three bolts that appear to be holding the tail shaft to the transfer case need to be removed. Gently pry on the tail shaft tabs, and the piece should come loose. Being that the construction is made up of aluminum be very careful, and do not force it. After removal is complete, you can physically see the brass bushing inside. It is very important to use an actual bushing driver to change out the bushing. Damaging the tail shaft housing through usage of a punch or a socket will result in excessive bypass of fluid, and replacement of the whole component will become necessary. Also, install the new rear seal while you still have the tail shaft on the bench. Clean both the transfer case and tail shaft with a gasket scraper, and re-silicone the piece before installation.

Of course, if you do not want to risk damaging your expensive transfer case, bring it to a reputable shop. But now you’ll know a little bit more when the guy at lube shop suggests that you repair your leak with a new seal.