Overdrive?

[goneape1]

Is there anything that is like and extension to my auto tranny that will serve as an overdrive? I have heard of two speed transfer cases....would this act like an overdrive?
I use my toy for mainly highway use but still want it trail capable. My fuel mileage is so aweful that you cant enjoy it.

[SGM O]

Your transfer case is a two speed. 1:1 and 2.72:1 assuming you have a stock case. There is a kit for automatics that acts as a doubler that fits in the auto tranny that would then give you 1:1, 2:1, 2.72:1 and 5.44:1 but none of these will help you on the highway. I have not researched an overdirve kit for a Jeep, but what you want is a way to drop your final gear in the transmission below 1:1. .9:1 would be considered overdrive. The issue then becomes do you have the torque/hp to maintain highway speed at the rpm the engine will be running at. An engine is most efficient at a certain rpm, say 2,000 - 2,200 rpm for the 4.0L six cyl, which should be about 60 mph. You could change the gears in your axles. They may taller gears, lower number, not sure what you have now, but most of us are going the other way because we want to run bigger tires and maintain our on street performance. You could try running one size larger tire. If you are running 235's try going up to a 245 or if they are 30" try running 31", this should not require any change in suspension, but your speedometer and odometer will be off slightly so to get an accurate mpg reading you will need to change your speedo gear or use a gps to calculate your mileage.

[Ricky Booby]

I hate to be the nag here, but we need more info. What type of Jeep, tires, gears, motor, tranny, etc. Then you may get the advice narrowed down a little more.

Bobby

[Shadow]

Does your tranny have OD? If it does then that would/should give you .65:1. A splitter will only give a lower gear ration not a higher. How many miles on the clock? Any shifting issues, does 1st to 3rd shift correctlly? When was the last time the fluid was changed? Then there is the engine itself, does it smoke, knock, leak? Whens the last time you replaced the plugs, plug wires, cap and rotor?