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Side view of early Warn
OD with shift rail out the front

 

The Saturn Overdrive (originally produced by Warn) is a bolt on 0.75:1 overdrive for Jeeps equipped with the Dana 18 transfer case. It is not a transmission exactly, but it will give you more gearing options. You can run lower gears in your differentials and still have good highway performance.

The Saturn Overdrive bolts on the PTO port on the Dana 18 and it works in all forward and reverse gears. There is a PTO adapter available for the Warn Overdrive that will allow you to bolt a PTO output to the back of the overdrive. Advanced Adapters lists the part, but has never produced it. It can be found used.

Side view of late Warn OD with shift rail out the back. Photo by Paul Weitlauf.

 

The Saturn/Warn Overdrive does not work with any other transfer case other than the Dana 18. It will not work with a Dana 20 or a Dana 300. The Dana 18 is sometimes called the Spicer 18. There are some pictures of the Dana 18 with the PTO plate removed on the transfer case page. The Warn Overdrive bolts on the back of the tranfercase and attaches to the transmission output shaft. It replaces the drive gear that normal bolts on there.

Warn OD installed in a Dana 18.

 

Talking with Paul Weitlauf, I realized there were more differences between the overdrives than I originally thought. I have a small hole Warn Overdrive on my CJ-2A and Paul has a big hole Warn Overdrive on his CJ-5. On his overdirve, the shift rail comes out the back of the case and on mine the shift rail comes out the front of the case.

I double checked the Advanced Adapters catalog and they show an overdrive with the shift rail coming out the back of the case. I'm not sure if all the new Saturn Overdrives have the shift rail out the back or only the big hole untis. A picture of Paul's overdrive is on the right.

Probably the most frequently asked question about the Warn/Saturn overdrive is, "How do I remove the overdrive?" Here are some instructions on how to remove it.

Removing a Warn Overdrive
From JeepTech, the Jeep knowledge base.  by Terry Howe

I get confused every time I remove a Warn (aka Saturn) over drive from a Dana 18 transfer case that was in a Jeep or Scout 80. Looking at the exploded view from Advanced Adapters helps, but sometimes I still get it wrong and I have to figure it out all over again. I figured if I wrote up the procedure, I wouldn't forget again and at least I'd have something to look up.

 

  • Remove the five bolts that run through the case of the over drive with a 9/16" socket.
  • Pry the over drive case away from the Dana 18 case. Keep in mind that the gasket sealer and the bearing that rides in the plenetary hub assembly may fight a bit.
  • Remove special snap ring that is behind and can be seen through the planetaries.
  • Remove the special lock washer that is behind the snap ring with some needle nose pliers.
  • Use long 1/2" extension to remove planetary hub assembly from transmission output shaft.

 

Back view of early Warn OD with shift rail out the front

 

 

 
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