Installing an Overdrive

One of the best additions you can put on your Willys is an overdrive unit, especially if you drive it a lot.  The overdrive unit will reduce your engine RPMs by about 25 percent and will allow your Willys to reach about 55 MPH without the engine screaming at high RPMs.  Overdrives are also good for engine conversions and high rear axle gear ratios for those who do a lot of off-roading.  Used overdrives go for about $500-$600 and a new Saturn like mine will set you back about $900.  Some good tech tips can be found on the CJ-3B Page, and Herm the Overdrive Guy is a good source for overdrive parts.  I purchased my overdrive from Mile Hi Jeep Rebuilders in Denver, CO.  The installation is relatively simple and should take you about 4 hours max.

Here is everything you need for the installation.  The shifter was an additional $75, but saved me the time of trying to fabricate one.

Remove the rear access cover.  Then remove the cotter pin, nut, and input gear.

The bowl gear slides right on.  See the star in the center of the gear?  Use a 1/2" extension and thread the special nut on.

Tighten to 100 to 130 ft lbs.

This is the hardest part:  Installing the lock washer and snap ring.  Instructions come in the kit, so make sure you follow them to the letter.  Install the lock washer and make sure it is seated correctly.  Then slip the snap ring in.

Using needle nose pliers or snap ring pliers, ensure the snap ring is seated in the groove.  If this is not done correctly, you can ruin your investment!

Next, the casing is installed, and using a little loc-tite, the bolts are tightened to 30 ft lbs.

The shift rail slides right in and is attached to the overdrive unit.

The shift kit comes with spacers and mounts pretty easily.


The shift kit is very well made but....

....You have to cut your transmission cover to clear the shifter bracket.

Here's the final shifter install

The kit comes with a new shifter ring and boot so the install looks fairly clean.