Warn Overdrive Rebuild—Making Jeeps Go Fast Again

    Rebuilding a Warn Overdrive

    Brian GabrielPhotographer, Writer

    Back in the day, old iron didn’t need to move very fast. A 50mph top speed flatfender Jeep did its job on the battlefield and on the farm in civilian life. It was a time when torque and grunt were more important than keeping up with traffic or how good your fuel economy was. It didn’t take long for the world to speed up, and before we knew it, factory 5.38:1 geared Jeeps with 1:1 final drive transmissions were being left in the dust.

    It was then that the Thompson brothers decided it was about time for some highway gearing options. Using some inspiration from an old Studebaker overdrive design, they created the first auxiliary bolt-on overdrive unit for the Dana 18 Jeep transfer case. Eventually, Warn industries ended up with the rights to the design and started mass production in 1962. For more history on the evolution of the overdrive, check out Jp article “Speeding up the Early Jeeps—Old School” (fourwheeler.com/how-to/transmission-drivetrain/154-0611-jeep-standards-capabilities-old-school).

    Fortunately, in today’s modern Jeep world there is a guy keeping these old overdrives alive. Herm The Overdrive Guy (hermtheoverdriveguy.com) is based out of Washington State and is the go-to guy for everything related to Warn, Husky, Dualmatic, and modern Saturn overdrives. Herm sells complete 25-percent overdrives or his signature 30-percent overdrive unit, in addition to offering rebuild services for all of the variations of overdrives for early Jeeps. When our Warn overdrive became jammed in OD and wouldn’t shift out, we limped it home and knew it was time to call Herm.

    Since we had plenty of experience rebuilding motors, transmissions, transfer cases, and axle gear setups, it seemed that rebuilding a small little overdrive unit would be no big deal. A quick call to Herm to order a rebuild kit changed our thought process. Despite our experience, Herm still steered us away from digging into an overdrive rebuild ourselves. Half of the battle is knowing how badly worn the reusable components are in your unit, and the other half is knowing the tricks to getting them apart and back together. Herm charges a super-affordable $45 flat labor rate (plus parts) that is designed to be the offer you can’t refuse. It is cheap insurance to know that your overdrive was rebuilt correctly and received all of the attention to detail it deserves. Herm let Jp get a sneak peek inside his shop to see what goes into a rebuild. If your overdrive is on the fritz, give Herm a call.

    Overdrive FAQ

    Here are some quick answers to some common questions regarding these overdrives:
    • For overdrive removal and installation techniques, we suggest consulting the instructions that can be found at hermtheoverdriveguy.com. You should never need to cut, torch, hammer, or use excessive force when removing or installing your overdrive. Permanent damage will be incurred.
    • Warn, Husky, Dualmatic, and Saturn are all equally strong and reliable.
    • It is okay to use your OD in low range; the input speed and torque to the OD from the transmission is the same as high range. The low range gear reduction occurs after the OD.
    • Big horsepower is not an issue. One of Herm’s customers is using an overdrive behind a Cummins 4BT pushing over 800 lb-ft of torque.
    • Lack of oil will damage an overdrive. Make sure the oil catch trough is properly installed and that the oil level in the transfer case is checked often.
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