[wrangler2002]

This is probably a stupid question but here it goes...

My assumption so far has been that my front diff (dana30) has a gear ratio of 3.07:1 (between the ring and pinion gears) and the rear (dana44) has a 3.73:1.

How is it possible, when 4-wheel drive is engaged, for the front wheels to rotate at the same speed as the rear wheels (not during a turn but driving in a perfectly straight line).

I always assumed that part-time 4wheel drive shouldn’t be used on dry pavement because it's hard on the tcase during turns… but it just hit me that its straining the tcase on straight lines as well…


If the 2 drive shafts spin at 1000RPMs then the front tires should spin at ~325 RPMs and the rear ~270 RPMs which is a significant enough diff that the jeep should not even be drivable on dry ground without a whooole lot of bucking/skidding. But I feel no bucking what so ever in a straight line. Turning is a different story.

[BigJeepJay]

Originally Posted by wrangler2002

How is it possible, when 4-wheel drive is engaged, for the front wheels to rotate at the same speed as the rear wheels (not during a turn but driving in a perfectly straight line).

It isn’t possible unless you have different size tires on your front than your rear. You do not have 3.73’s and 3.07’s in your Jeep. I believe if you have an 4.0L auto you have 3.73’s both front and rear but if you have the 5-speed than you definitely have 3.07’s. If you only drive in 2WD then only your rear gears matter but when engaging 4WD both axles need to be geared them same for the same size tires.

[T.H's TJ]

U can have 3.73 in a 5sp. Crawl under your jeep and check out the tag on the diff it will tell ya.

[BigJeepJay]

Originally Posted by T.H's TJ

U can have 3.73 in a 5sp. Crawl under your jeep and check out the tag on the diff it will tell ya.

When did that come from the factory?

…nevermind I think it possibly came as a option with the oversize (30”) tire group.

[TJeeper]

You made a bad assumption. Both the front and rear diffs are the same gearing (or as close as possible considering the physical size of the r&p, e.g. 4.10 and 4.11). If they weren't, your transfer case would have been destroyed a long time ago.

Never use part time 4WD on the road. Even though the diffs are geared the same, and it is ok to go in a straight line, when you turn the front and rear driveshafts are going to rotate at different speeds. If they are locked together (as they are in 4WD), and the tires are not allowed to slip (like on dirt or snow), the transfer case will bind up, which could damage it.

[Wheelin98TJ]

3.07 is a possibility for an auto 4.0L.

Thats what mine had originally.

[BigJeepJay]

Originally Posted by Wheelin98TJ

3.07 is a possibility for an auto 4.0L.

Thats what mine had originally.

That seems pretty high for an auto...surprising.

[wrangler2002]

For the 2002 Sport i'm pretty sure if you upgraded to the 30inch tires you also got the dana44 plus the 3.73 gear ratios... i had just assumed that the 3.73 was for the rear only.

Thanks for clearing it up.

[wrangler2002]

atleast for the manual. don't know for the auto

[RafaelSmith]

Originally Posted by JeepJay3279

That seems pretty high for an auto...surprising.

My 2000 4.0l w/ 3sp Auto came with 3.07 as well.

Wasnt to bad with stock tires...for the week I had them =P

But when i put 31's on it really sucked.

re-geared to 3.73 and its nice both on road and offroad.

[Varnish]

Originally Posted by JeepJay3279

I believe if you have an 4.0L auto you have 3.73’s both front and rear but if you have the 5-speed than you definitely have 3.07’s.

From what I can tell its a crapshoot, my friend and I had the exact opposite, 3.07s in my auto & 3.73 in his 5 speed. If anything, the auto is more likely to have 3.07s due to the lack of overdrive, but who knows without checking the axle.

[outdrsman]

I just purchased my first jeep last March. I have an 01 with the 4.0 and 3sp auto and 3.07 gears. I'm running 33's on it. I went to the dealer and they gave me a printout.