Changing Gear Ratios

[dvdmacdaddy]

I have a 99 TJ with a 4.0L engine, Dana 35 3.73 rear axle, dana 30 3.07 front axle and running 32in tires, when we go 4wheeling we swap to 33's, with a 4in lift. I have a Dana 44 rear axle on the way with 4.10 gears do I need to re-gear the front axle to match the rear axle. Is a 4.10 gearing going to help much, my problem is running down the highway with the 32's I have to down shift to 4th often to keep 70mph.

I am guessing the rear axle is a 3.73, I jacked up the rear end spun the tire once and the driveshaft rotated approx 3 3/4 turns.

 

[SteelHeadz]

Welcome to Jeepz. I don't see how you can run on 3.73 gears on the rear and 3.07's on the front axle. Somethings bound to break or show a severe premature wear . P.M. me the last eight digit of your VIN# and i'll look at the build sheet and see what originally came with your Jeep granted that it's still the factory stock axles and gears.

 

[phall92139]

I agree with Mikey here, somethings up if you are running 3.07 gears in the front axle and 3.73's in the rear. While it's not an absolute must for the front and rear gear ratios to be identical they need to be within 1% for on-road use and you might be able to get away with as much as 2% off-road. However, your stated set-up is out of these boundaries:

3.73/3.07 = 1.2149 which equates to a difference of almost 22%​

This would be placing an incredible amount of undue strain on your drive train. In simple terms...your front and rear gear ratios should be the same.

Also, I don't think you are going to see much performance change going from 3.73 to 4.10 gears. You will see somewhere in the neighborhood of 200-300 more RPM's at 65 mph, still have a good daily driver getting pretty good gas mileage but not tons of low end.​

 

[dvdmacdaddy]

Welcome to Jeepz. I don't see how you can run on 3.73 gears on the rear and 3.07's on the front axle. Somethings bound to break or show a severe premature wear . P.M. me the last eight digit of your VIN# and i'll look at the build sheet and see what originally came with your Jeep granted that it's still the factory stock axles and gears.

According to the vin they are both 3.07, thanks for the info via PM. . We bought this Jeep used from a guy that went to some Jeep Jamboree's and he has done some work to it. So there is no telling if the gearing has been changed already or not, we have tried to contact him but have not been successful. I guess its time to change the gear oil and while there count the number of teeth. We are looking to get a balance between on and off road performance. Most of the trails we go on we end up 50-100 Hwy miles away from camp. We have been known to go on 2 day trips and end up 200 Hwy miles away.

 

[jfrabat]

You can pop open the Diff covers and read the number of teeth stamped on the ring... Or count the tooth. Then divide one over the other and you get the ratio.