Lower Final Drive Options

[bbaldwin237]

Thanks for your expertise and bearing with me as I learn this stuff. I confirmed my TJ 6MT has Dana 30 front and Dana 44 rear with 3.73 gears. This is probably why 4th is pretty good on the highway. 5th effective only on the flats or downhill. I am between 4.88 and 5.13 but the consensus here is the latter. If I do go the regear path should I consider Dana 44 swap up front?

If you're saying it's a "poser Jeep" there is no reason to go to the 44 vs the 30. The 30 is plenty strong when built for 35s.

 

[Hit_Apex]

If you're saying it's a "poser Jeep" there is no reason to go to the 44 vs the 30. The 30 is plenty strong when built for 35s.

My thought as well - thank you!

 

[L J]

If I do go the regear path should I consider Dana 44 swap up front?

The only real benefit of the front Rubicon 44 is the ability of those with the 42rle auto trans to run 5.38 gears.

 

[Rickyd]

The only real benefit of the front Rubicon 44 is the ability of those with the 42rle auto trans to run 5.38 gears.

The stock rubicon lockers certainly aren't much of a plus

 

[jjvw]

The stock rubicon lockers certainly much of a plus

Until they aren't.

 

[L J]

The stock rubicon lockers certainly much of a plus

You, of course, meant certainly NOT much of a plus.

 

[Rickyd]

aren't

Oops, that was a crucial omission!

 

[NashvilleTJ]

Oops, that was a crucial omission!

We knew what you meant, Rick.



Really, we knew what you meant...



No, really...



Hey wait, why is everyone laughing???

 

[Rickyd]

We knew what you meant, Rick.



Really, we knew what you meant...



No, really...



Hey wait, why is everyone laughing???

They're all laughing with me!

Right!?!

 

[Wildman]

Thanks for your expertise and bearing with me as I learn this stuff. I confirmed my TJ 6MT has Dana 30 front and Dana 44 rear with 3.73 gears. This is probably why 4th is pretty good on the highway. 5th effective only on the flats or downhill. I am between 4.88 and 5.13 but the consensus here is the latter. If I do go the regear path should I consider Dana 44 swap up front?

Here's a great tool to help figuring this out with. I put in your info using 33.3" tall tire since you said you have 34" tires and they rarely measure their advertised height. Then put in 5.13 gears. In 4th @ 70 MPH with the 3.73 gears you're turning 2635 RPM's (you can verify this easily) then in 5th with 5.13 gears @ 70 MPH you'd be turning 2645 RPM's. So that should answer your question about 5.13's or 4.88's. Technically you'd want even lower gearing since your larger tires have more rolling resistance & sitting higher causes more wind resistance so to overcome that you'd want 5.38 gears.

https://www.grimmjeeper.com/gears.html

 

[Hit_Apex]

Thanks for the calcs, Very helpful and supportive of 5.13 minimum. Amazing how big tires impact this, i know it's just math and spinning circles but eye-opening for someone new to off-road configs.