writer: Sean P. Holman
photographer: Sean P. Holman
The robust 134ci Go-Devil flat four that resides under the hood of Project Colonel Mustard, once heralded for its power, produces about 60 hp and 105 lb-ft of torque. The three-speed T-90 transmission had enough gears for the rural roads of the day that the Willys CJs were expected to traverse, but in today's fast-paced world, we find it hard to hold 55 mph on the freeway and feel good about the 3,600 rpm the engine is spinning when the redline is only 4,000 rpm.
The Colonel's dash plate says the maximum speed in Third gear high-range is 60 mph. Well, anyone who owns a flattie with the Go-Devil engine in it can tell you that this is on a good day downhill with the wind at your back.
Enter Advance Adapters' excellent Saturn Overdrive. Thanks to the Dana 18 transfercase design, Advance Adapters' Saturn Overdrive can be installed in an afternoon even if you have never done it before. Because the overdrive unit utilizes the PTO output shaft, there are no modifications needed to the driveline. This makes for a cost-effective and simple upgrade. Plus, these little guys are made strong, easily holding up to the torque of a small-block V-8, let alone the limited output of our Go-Devil.
The overdrive also reduces engine revs by 25 percent, making 55 mph a much more comfortable affair (hmm, suddenly the brakes and steering seem to need attention). The other bonus is a myriad of gearing possibilities, now that the Colonel has a total of 12 forward and 4 reverse gears. In those trail situations where we find First is too low and Second too high, we now have the ability to find the perfect gear in overdrive First.
For the install, we headed over to see Mel Wade at Off Road Evolution in Fullerton, California, who we know to be a true flattie fanatic.
1. The Saturn Overdrive kit comes with everything you need for the install, including a new linkage and shifter. | 
2. First, we removed the rear PTO cover from the transfer case and removed the input gear. | 
3. The input gear (foreground) is replaced by the Saturn Overdrive bowl gear (left rear). |
4. With the bowl gear in place, we torqued it down to just over 100 lb-ft. | 
5. The most diffi cult part of the process is installing the star-shaped lock washer and snap ring. | 
6. Once we were sure the lock washer and snap ring were seated properly, we installed the overdrive unit. |
7. Next, the shift rail is attached to the Saturn Overdrive unit. | 
8. The shifter mounts and lever are connected to the slide and adjusted. Advance Adapters provides a new boot and ring that will need to be shaped, while the stock transmission cover will need to be cut. The finished install does look clean, though. | 
9. Marked with a cue ball for a shift knob, the overdrive shifter looks at home in our forest of levers, but most importantly, we can now enjoy lower stress and better fuel economy on those adventures to the trailhead. |