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What gears do I want?

Michelobe

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Let's start with the particulars. 2005 TJ with a 4.0 and auto transmission with OD and Dana 35, Dana 30 with 3.73 gears and 32" tires. I live in the mountains in western NC and my current setup sucks. I've been watching Craig's List and Facebook Marketplace for axles. Today a guy post with a Dana 35, Dana 30 with 4.10 for $1000. After talking to him he mentioned that he has a set of Dana 35, Dana 30 with 4.56 for $1200. He has just let me know he'll give me $400 for my axles. I don't currently have any interest in going to 33" tires. Am I foolish to to trade my current axles and $800 for a set of 4.56 axles?
 

Rubicon88

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You can never have too much gearing..

That said it seems to me you aren't going to swap gears yourself.
You're looking at $$$ for a shop to do it...

4.10 would be negligible.

4.56 will be a nice improvement from what you have.

In a sense that's a re-gear to 4.56 for $400 per axle...

You'll never get close to that paying for parts and having a shop do it.
Chew on that.
 
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L J

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Regearing isn't inexpensive so you'll want to consider a few things so that if you have to spend a sizeable amount of money you do it right and only once.

How long are you going to keep the Jeep?
Do you take it off-road much or at all?
Are you staying with 32" tires in the long term?
Have you thought about adding lockers or limited slips to the Jeep?
 

CharlesHS

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The amount the guy is asking for the used differentials / gearing, you really don't know how the gears were treated plus the amount of your labor to swap the differentials; IF your budget can afford the $2000 to regear the Dana 30 and Dana 35 you will be much better off with the 4.88 gearing. Not only from the drivability in the mountains (as Jerry posted above), but now you have new gears, bearings, seals and you know what the condition of the parts are instead of buying used differentials that barely have adequate gearing for your tire and transmission combination.
 
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Michelobe

Michelobe

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Thanks for the input everyone. The recommended guy in my area for doing gears has closed his shop. He was tired of working 80 hrs a week. I guess it's time to find someone else and get 4.88s (damn that sounds steep) and maybe look at lockers.
 
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SvtLdr

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Or learn to set up gears yourself? It's really not that bad of a job, especially if you have a couple of buddies that want to learn with you. You can split up the cost of a few specialty tools you'll need.
 
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JMT

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456 is substantially better than 373 for 32’s and $800 is cheap compared to parts and labor to regear to 488 (~$2000). That would be a lot of money to pour into a Dana 35. If you’re staying with 32’s, I’d go the cheap route. You will be very happy. Add a lunchbox locker up front and go a lot of places!

I wouldn’t lock the Dana 35 without doing a super35
 

CharlesHS

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I wouldn’t lock the Dana 35 without doing a super35
I have observed on the trail in Moab several times what happens when you install a locker in a Dana 35 with 27 spline axles. You twist off the end splines which remain inside the carrier and the axles slide out the axle tube.
Exactly why I installed a Detroit TT LS....
 
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Rubicon88

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I think you need to take a breath and revisit why you put this question up here.
It wasnt to run 35" tires or larger...
It wasnt to run the Rubicon or Moab.
You weren't conplaining of a traction problem on the trail...

From what I gathered your issue is just a lack of power running 32's on the paved hills of North Carolina.
In other words you're looking for sonething to help maintain your road speed a bit better traveling the hilly terrain you reside in. No?

Have you looked at any gear charts? While they're not perfect because they don't factor in terrain and extra tire weight they will accurately show you the factual rpm. That's completely in lieu of terrain and extra weight.
MPH and RPM don't care about terrain and weight.
In your case you're not moving up in tire size so an added tire weight is null.
You are the only one that knows your terrain and if the rpm change will be enough to help you.
The below chart is running at 65 mph. These gear charts are all based on a 1:1 final drive ratio.
Your automatic would mean 3rd gear.
gear_ratio_chart.png


You're running approximately 2546 rpm at 65 mph. Not knowing your exact tire diameter it won't be exactly 2546 rpm but very close.
Again not knowing if you changed your speedo for running 32's over
29"ish stock tires's your speedo will be off a bit.

All that aside the facts remain your 3.73 gears and a true 32" tire will get you 2546 rpm at a true 65 m.p.h. with a 1:1 final drive.
You can just multiply this rpm by .69 and get your rpm in overdrive @65 mph
At present your rpm in overdrive @65 mph will be
at or near 1,750 rpm.

4.56 gears will put your rpm nearly 600 higher at 3112 rpm @65 mph with a 1:1 drive ratio (3rd gear)
In OD youll be at or near
2,148 rpm @65mph

Thats a nice improvement over what you have now.

4.88's in overdrive will get 2298 rpm @65

Weighing all things such as your initial goal here...

I think you'll find a very nice improvement over what you have now in the 4.56. Considering it's a nice upgrade for only $400 per axle.

Perhaps you show up with cash you can get it even cheaper.


Good luck in your endeavor
 

JMT

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I think you need to take a breath and revisit why you put this question up here.
It wasnt to run 35" tires or larger...
It wasnt to run the Rubicon or Moab.
You weren't conplaining of a traction problem on the trail...

From what I gathered your issue is just a lack of power running 32's on the paved hills of North Carolina.
In other words you're looking for sonething to help maintain your road speed a bit better traveling the hilly terrain you reside in. No?

Have you looked at any gear charts? While they're not perfect because they don't factor in terrain and extra tire weight they will accurately show you the factual rpm. That's completely in lieu of terrain and extra weight.
MPH and RPM don't care about terrain and weight.
In your case you're not moving up in tire size so an added tire weight is null.
You are the only one that knows your terrain and if the rpm change will be enough to help you.
The below chart is running at 65 mph. These gear charts are all based on a 1:1 final drive ratio.
Your automatic would mean 3rd gear.
View attachment 256319

You're running approximately 2546 rpm at 65 mph. Not knowing your exact tire diameter it won't be exactly 2546 rpm but very close.
Again not knowing if you changed your speedo for running 32's over
29"ish stock tires's your speedo will be off a bit.

All that aside the facts remain your 3.73 gears and a true 32" tire will get you 2546 rpm at a true 65 m.p.h. with a 1:1 final drive.
You can just multiply this rpm by .69 and get your rpm in overdrive @65 mph
At present your rpm in overdrive @65 mph will be
at or near 1,750 rpm.

4.56 gears will put your rpm nearly 600 higher at 3112 rpm @65 mph with a 1:1 drive ratio (3rd gear)
In OD youll be at or near
2,148 rpm @65mph

Thats a nice improvement over what you have now.

4.88's in overdrive will get 2298 rpm @65

Weighing all things such as your initial goal here...

I think you'll find a very nice improvement over what you have now in the 4.56. Considering it's a nice upgrade for only $400 per axle.

Perhaps you show up with cash you can get it even cheaper.


Good luck in your endeavor
I second all of this^^^^Please pay attention to this post, especially the part where 456 rpm's (2148) are compared with 488 rpms (2298) at 65mph. There is not $1200 worth of difference there in my opinion for your purposes.

If I lived in NC and had your goals, I would have already been over there with cash in hand. I also have an 04' with the 42rle, 32's and 373 gears, so I know how it drives now.
 
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Rubicon88

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I second all of this^^^^Please pay attention to this post, especially the part where 456 rpm's (2148) are compared with 488 rpms (2298) at 65mph. There is not $1200 worth of difference there in my opinion for your purposes.

If I lived in NC and had your goals, I would have already been over there with cash in hand. I also have an 04' with the 42rle, 32's and 373 gears, so I know how it drives now.
Exactly...
And don't lose sight of your original intention.
Moreover to regear your current axles it will not be $1200.
You will be faced with lockers or not. Which ones. Might as well do it now since all that shit has to come out if installing one (minus the lunchbox lockers)
Upgrade axles...or not.

When all you wanted was to run with more oomph.

I can appreciate the pain. While I don't like automatic's in Jeeps I can appreciate the hill dilemma. I literally can't drive a mile in any direction without hitting a hill. Some more daunting than others but hills all over the place.

For $400 per axle for more power to basically roll under and go...
 
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roverhi

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Using the above gear chart the 42RLE overdrive brings the RPM with 3.73 gearing down to 1813rpm on 31" tires. That's a barely usable gear ratio on flat ground with a tailwind. In 3rd it's a little high 2628rpm but you lose the transmission lockup which hurts fuel economy. Just an inch larger tire 32" tire looks to make the 4th overdrive with lockup mostly unusable. Seems if you care about fuel economy AND performance on 31" tires, 4.56 would be the minimal gearing. Even with the stock 29" tires and 3.73 gearing, rpm at 65 doesn't break through 2,000rpm. Why didn't Jeep use 4.10 gearing with the 42RLE?? That seems the minimum gearing for the dinky stock tires let alone any tire upsize. Looking at the chart now see why people say go all the way to 5.13 if you are thinking of re-gearing with the 42RLE. Appears that stock gearing is designed for the low end grunt of a Diesel not the higher rpm/torque specs. of the 4.0.
 
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jjvw

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42rle/31.5”/3.73=2059rpm @ 75mph
42rle/31.5”/4.10=2263rpm @ 75mph
42rle/31.5”/4.56=2517rpm @ 75mph
42rle/31.5”/4.88=2694rpm @ 75mph
42rle/31.5”/5.13=2832rpm @ 75mph
42rle/31.5”/5.38=2970rpm @ 75mph

I vote 5.13 because you can't do 5.38. If the Dana 35 can't do 5.13, then you are stuck with 4.88.
 

Steel City 06

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Personally I would go straight to 5.13 myself.

And here is why:

Once you gear past about 4.10 or so, you're going to lose the ability to use 2nd gear at freeway speeds. But at the same time, you're also going to make 4th gear more usable. 3rd will become your replacement for 2nd, and the deeper you gear, the more useful it will be at freeway speeds.

So let's say you're rolling down a freeway at 75 mph. You hit a big hill. Currently you could shift to 3rd and run 3032 RPM for a modest boost in propulsive force, or shift to 2nd and run 4760 (probably closer to 5000 with the torque converter slip) for maximum power to get maximum propulsive force at the ground at that speed.

Once you gear any higher than that, you lose the ability to use 2nd gear on the highway. But as long as you gear appropriately for 3rd and 4th, that's not an issue.

With 5.13 gears, at 75 mph you would be running about 4170 RPM in 3rd (probably closer to 4400 RPM with the torque converter unlocked), which puts you very close to the peak HP RPM (4500 RPM). I would dare say you may get more propulsive force in 3rd with 5.13 than 2nd with 3.73 at 75 mph.

And 5.13 in 4th gear would be turning 2877 RPM at 75 when the torque converter locks. That is still fewer RPMs than several different factory combinations, including the 6 speed Rubicon and some of the 3 speed automatic options. So in 4th that gearing is very reasonable.

So in short, 5.13 would be a great gearing for mountain freeways, and would also be awesome tooling around town or on the trails. If you lived somewhere flat like North Dakota, maybe something taller might be fine.
 
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Michelobe

Michelobe

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To much info, just kidding. A lot of good info for me to think about.

Rubicon88, that's a lot of info to think over and it makes sense. If I spend the $800 and go to 4.56 and I'm still not happy with it at least it'll be better. Then I can can go from there if I feel I need more.


Steel City 06, I grew up just outside of Pittsburgh so I know the terrain. Curious what tires and gears you're running? What you said sounds good but I could never talk myself into trying 5.13 without trying something in between. 5.13 just seem like such a huge step.

 
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