The three Spicer Model 18 Transfer Cases used on Willys four wheel drive vehicles are very similar. Many of the parts are interchangeable and the sequence of disassembly and assembly is the same.
The Spicer Model 18 Transfer Case is essentially a two speed transmission located at the rear of the standard transmission which provides a low and direct gear for any selection of the transmission gears and also a means of connecting and disconnecting power to the front axle.
The shifting mechanism is operated by two levers on the top of the case. A power take-off aperture is located at the left rear just behind the transmission main shaft. A transmission overdrive can also be installed here.
The speedometer drive gear is located inside the rear output shaft housing and the hand brake on some models is located on the same housing.
The transfer case gears are controlled by the driver through the left side lever that provides two and four wheel drive selection and the right side lever that provides high and low gear selection.
The neutral position of the high and low gear lever disengages all power to the wheels and is used to provide the neutral setting necessary for use of various power take-off equipment when the vehicle is stationary. The neutral position is also used when towing the vehicle.
The three Model 18 transfer cases are easily identifiable while still installed in the vehicle. This is a simple matter of crawling under the vehicle and looking at the rear of the transfer case housing and determining the diameter of the intermediate shaft.
The intermediate shaft is located in the center of the housing and is held in place with a lock plate and a 9/16" hex head bolt.
Using a ruler or caliper, measure the diameter of the intermediate shaft. There are only three options: 3/4 inch, 1 1/8 inch, and 1 1/4 inch.
Once the intermediate shaft diameter has been determined, click on the appropriate subgroup at the lower right of this page.
It is your responsibility to correctly identify your transfer case before ordering parts!
Again, many of the parts of these transfer cases are interchangeable and all three transfer cases can be installed in any Willys four wheel drive vehicle. The transfer case in your vehicle may not be the original or the correct one for your vehicle.
The gear ratios of the three Model 18 transfer cases are as follows: