Best gear ratio for Dana 30 front and Dana 44 rear?

[Jaime Rangel]

Hello everyone, I am new to the jeep community, I have a TJ 2005 4.0L automatic transmission, I bought it 6 months ago second hand and I am making improvements... I was looking for an answer to my question in the forum, but I did not find it, I apologize if this question was already clarified.
I currently have stock Dana 30 front and Dana 44 rear differentials, 33s tires... I want to put 37s tires I have read in the forum that you have to change the ratio of the differentials but which is better for my configuration 4.56 or 4.88.

I'm thinking of buying the Yukon kit

https://www.quadratec.com/p/yukon-g...tall-kits-jeep-wrangler-dana-30-front-dana-44

 

[Duck Doctor]

Your axles lack sufficient strength to run 37” tires. Best you can do with those axles is 5.13 gearing, chromoly axle shafts, and 35” tires.

 

[PNW_LJ]

With your axles, the deepest gear ratio you can do is 5.13.

With your auto transmission (42RLE), that is an ideal ratio for 33s.

If you swapped in a dana 44 in front, you could run 5.38 gearing, which is typically used with 35s.

 

[TexasTJ2004]

Yeah, as folks here wrote, you can get maximum 5.13 for your axles.
5.13 is optimal for 33s. The upper you go in tire, the more lugging the engine will be.
35s is realistically maximum that you can run reliably on this combo, if you plan to wheel it.
If you stick to 33s and install 5.13 ratio, it would work perfect for you.
You stock shafts will work just fine with 33s

 

[Jaime Rangel]

Yeah, as folks here wrote, you can get maximum 5.13 for your axles.
5.13 is optimal for 33s. The upper you go in tire, the more lugging the engine will be.
35s is realistically maximum that you can run reliably on this combo, if you plan to wheel it.
If you stick to 33s and install 5.13 ratio, it would work perfect for you.
You stock shafts will work just fine with 33s

Do you recommend any specific brand or kit to put the 5.13 ratio on my dana 30 and dana 44?

 

[Jerry Bransford]

Do you recommend any specific brand or kit to put the 5.13 ratio on my dana 30 and dana 44?

https://www.revolutiongear.com/. Just so you know, the 5.13 is recommended over 4.56 or 4.88 due to your 4-speed automatic's stupid-steep Overdrive ratio of .69 that lowers the highway rpms way too much. For 35's 5.13 is barely enough, 5.38 is better but you can't install 5.38 into a Dana 30. And your front axle is not strong enough for 37's, not to mention 5.13 isn't enough gear for 37's. It's barely suitable for 35's.

 

[Jaime Rangel]

https://www.revolutiongear.com/. Just so you know, the 5.13 is recommended over 4.56 or 4.88 due to your 4-speed automatic's stupid-steep Overdrive ratio of .69 that lowers the highway rpms way too much. For 35's 5.13 is barely enough, 5.38 is better but you can't install 5.38 into a Dana 30. And your front axle is not strong enough for 37's, not to mention 5.13 isn't enough gear for 37's. It's barely suitable for 35's.

I appreciate your answer and teaching, thank you

 

[jjvw]

Yeah, as folks here wrote, you can get maximum 5.13 for your axles.
5.13 is optimal for 33s. The upper you go in tire, the more lugging the engine will be.
35s is realistically maximum that you can run reliably on this combo, if you plan to wheel it.
If you stick to 33s and install 5.13 ratio, it would work perfect for you.
You stock shafts will work just fine with 33s

The reality with the 42rle is that 5.38 is just about optimal for 33s. Any larger tire size is just a necessary compromise to what we have to work with. The only reason people say otherwise is because they don't do the math.

 

[TexasTJ2004]

The reality with the 42rle is that 5.38 is just about optimal for 33s. Any larger tire size is just a necessary compromise to what we have to work with. The only reason people say otherwise is because they don't do the math.

I am running 4.56 with 31s with my 42RLE and 4.0.
I think that it is adequate, as I get 2500RPM at 70MPH.
The question is which RPM you believe you should had at 70MPH?

 

[jjvw]

I am running 4.56 with 31s with my 42RLE and 4.0.
I think that it is adequate, as I get 2500RPM at 70MPH.
The question is which RPM you believe you should had at 70MPH?

3k rpm at 75mph has long been a goal. However, that is less than the early TJ with the 32rh did off the assembly line, which suggests that none of the gearing recommendations for 25 years are deep enough. Even the ones guys clutch their pearls over thinking the rpms are too high.

 

[TexasTJ2004]

I would say that 3K at 75 sound little too high for me.
I am in Texas Houston area where everything is flat as a tile. 2500RPM provides enough punch to drive at 70MPH and I can get to 80MPH pretty easily.

 

[machoheadgames]

3k rpm at 75mph has long been a goal. However, that is less than the early TJ with the 32rh did off the assembly line, which suggests that none of the gearing recommendations for 25 years are deep enough. Even the ones guys clutch their pearls over thinking the rpms are too high.

I think 3k at 75 is good, I don’t think the fact of the 3-speed revving even higher from the factory means all the others need to as well. Like anything, it was chosen as a compromise, for its very small gear spread.

I like low gearing and higher rpm but I think there becomes a point where more is not needed, and 3k at 75 seems to be that point, in my opinion anyways.

 

[Rickyd]

2.73 gears ftw

 

[jjvw]

I think 3k at 75 is good, I don’t think the fact of the 3-speed revving even higher from the factory means all the others need to as well. Like anything, it was chosen as a compromise, for its very small gear spread.

I like low gearing and higher rpm but I think there becomes a point where more is not needed, and 3k at 75 seems to be that point, in my opinion anyways.

The good confusing news is that at 75mph Jeep gave us about a 950rpm variance from 97-06. Even better was then never adjusting the gearing for the transmission. All Rubicons came with 4.10 despite having three very different transmissions.

 

[TexasTJ2004]

The good confusing news is that at 75mph Jeep gave us about a 950rpm variance from 97-06. Even better was then never adjusting the gearing for the transmission. All Rubicons came with 4.10 despite having three very different transmissions.

I am 100% that TJR Auto was under geared from the factory and TJR Manual 6 speed was over geared.

 

[machoheadgames]

The good confusing news is that at 75mph Jeep gave us about a 950rpm variance from 97-06. Even better was then never adjusting the gearing for the transmission. All Rubicons came with 4.10 despite having three very different transmissions.

I am well aware.

 

[mrblaine]

I think 3k at 75 is good, I don’t think the fact of the 3-speed revving even higher from the factory means all the others need to as well. Like anything, it was chosen as a compromise, for its very small gear spread.

I like low gearing and higher rpm but I think there becomes a point where more is not needed, and 3k at 75 seems to be that point, in my opinion anyways.

Others needing to or not isn't really the point. Jeep did that while at the same time being obligated to cover the vehicles under various mileage and time frame warranties. If the RPM were an issue, they would have seriously altered the ratio offerings and stuck everyone with 3.55's to keep the warranty issues down.

 

[machoheadgames]

Others needing to or not isn't really the point. Jeep did that while at the same time being obligated to cover the vehicles under various mileage and time frame warranties. If the RPM were an issue, they would have seriously altered the ratio offerings and stuck everyone with 3.55's to keep the warranty issues down.

I'm aware....I'm not concerned about RPM, nor was Jeep, and that wasn't my argument. I just don't think we need to gear other transmissions to run the same final drive as the 3 speed simply because the 3 speed did. The 3 speed did because it needed to. I'm not arguing for 4.10's on 35's or any other similar subpar setup. FWIW, I would do 5.38 on 33's with the auto and 5.89 on 35's, similar to how I like 4.56/31, 4.88/33, and 5.13/35 on the 5-speeds.

All I'm saying is with the logic I countered above, the 5 speeds should be gearing to 5.38 for 33's. I think there reaches a point where more gear isn't necessarily desirable, and basing the decision off of only the factory 3 speed's final drive, isn't logical to me.

 

[mrblaine]

I'm aware....I'm not concerned about RPM,

Then how did you arrive at 75MPH at 3000 RPM as being good?

 

[machoheadgames]

Then how did you arrive at 75MPH at 3000 RPM as being good?

Trying different setups. It cruises well up grades, still has 4th gear for really steep grades when needed (5-speed), gets reasonable mpg, has a good gear spread. In other words, I have not needed more than that. But, it helps that I have a 5 speed.

The 3 speed that we are modeling off of can't downshift past about 75 mph due to redline so it needs all the help it can get in top gear, not to mention low end performance.

I don't have it in my head that 3000 is a hard line that must not be crossed, like many do. I'd happily cruise 85 mph at 3500 rpm. I just have found that 3000@75 works well and haven't needed more. For many years, what the 'experts' suggested put 75 more around 2800 rpm, and I didn't care for that.