Over the years, two common types of aftermarket overdrives could be added to the Jeep Universal vehicles.
PTO Overdrives
For civilian jeeps and other 4-wheel drive vehicles, the most common aftermarket overdrive type is the PTO overdrive. PTO overdrives were manufactured by Warn, Husky and Dualmatic. New units are still in production by Advance Adapters and by ATV Manufacturing. I refer to these units as PTO overdrives since they bolt onto the Jeep drivetrain using the PTO port on the Dana 18 transfer case.
The extensive use of the Dana 18 Transfer case in other vehicle types means that many other makes and models of 4-wheel drive vehicles, such as Ford Broncos, International Harvester Scout and Scout IIs, Mahindra and Mitsubishi Jeeps can also use a PTO overdrive for improved performance on and off-road.
Borg-Warner R10 Overdrives
The Borg-Warner R10 overdrive units were used in a wide variety of 2-wheel drive vehicles including the Jeep Pick-Up and Wagon. They were also a popular factory option for many 2-wheel drive cars and trucks as well as hot rods.
When installed on a Jeep Pick-Up or Wagon, the BW R10 overdrive bolts onto the rear-wheel output of the Dana 18 or Dana-20 transfer cases and provides a 20% overdrive ratio when the vehicles is in 2WD. BW R10 units cannot be used when the vehicle is in 4-wheel drive.