XJ Waterproofing

The Ocala Jeep Club of Florida

Waterproofing critical drivetrain components is an essential part of prepping your Jeep for Florida wheeling, and doing so in a XJ has some special considerations due to it’s drivetrain and unibody design. Three particular issues will be discussed below:

Most XJ’s are equipped with the robust 4 speed Aisin AW4 automatic. The transmission is equipped with a drain plug in the transmission pan that makes draining contaminated fluid a breeze. The AW4 is also equipped with a external vent tube that is on top of the transmission near the bellhousing. Unfortunately the metal tube has a very short rubber hose extension that is capped with a plastic plug and brought into the engine compartment. There, it is zip tied onto the transmission kick-down cable near the tranny dipstick at a height that is no taller than the top of the transmission tunnel. Water may enter the transmission through the vent if it is splashed up to this level.

On XJ’s equipped with the NP231 transfer case, the transfer case has its own vent tube near the transmission adapter plate that is connected to an extension hose. This hose runs to the top of the bellhousing where it terminates in an uncapped U-shaped metal tube that is clipped to the back of the engine block. This is a poor design, and water easily enters the vent if the Jeep is briefly submerged to a level above the top of the bellhousing.

Whereas the front differential has a conventional vent that extends to a high location near the top of the radiator support, the rear axle has a much poorer vent design. A short vent hose runs from the brake line junction block on the axle to a drilled hole in the unibody frame rail, where it is held in by a simple nylon plug. Water can easily enter if the frame is submerged below water.

To To remedy this, I used 12 feet of 5/16” fuel hose to extend these vents. The transmission and transfer case are vented through a common hose that is split by a nylon T-connector to two short segments that connect to the transmission and transfer case vent tubes. I capped the vent hose with a Purolator HP2011 fuel filter that has an anti-siphon design to prevent water from entering through it. (Be sure that the end marked with an arrow and the word “to Carb” is connected to the hose). The filter is zip tied to the top of the firewall above the transmission dip stick. You can also use the HP2011 for the front axle vent. Be sure to save the OEM plastic cap that was on the end of the original transmission vent hose.

I vented the rear diff through the gas filler compartment, using a step drill to make a 3/8” hole in the metal flange that supports the fuel filler neck. The hole is placed to the left of the fuel filler neck where the flange is especially wide. A piece of 5/16” hose is passed through the hole and down towards the bottom of the rear fender behind the wheel well. Underneath the Jeep, the metal fuel filler pipe is protected as it enters the fuel tank by a thin sheet metal cap that is fixed by four sheet metal screws. I loosened the screws and bent back one of the corners of the cap and pulled the hose through the opening. The hose is then routed around the front corner of the gas tank, behind one of the mounting straps of the tank, and is loosely zip tied to the metal brake lines before being reconnected to the axle vent tube. Be sure the hose is long enough to have enough slack at full axle droop. Remember that plastic cap that you were supposed to have saved? Push the cap onto the opposite end of the axle vent that is by the gas cap, and zip tie the hose to the metal spring that keeps the access door closed.