Can I swap my 3.07 gears into a 3.73 posi rear axle?

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TJTony

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Gentlemen;

Is there a reason that the following question is not accepted?

I have an '05 Wrangler 4.0 with a 6 speed tranny, 3:07 non-posi rear end and 31" tires. Can I swap these 3:07 gears into a 3:73 posi rear axle?
 
I think the answer is yes if you have two D44s and no if you have two D35s. The carrier break for the Dana 35 is 3.31/3.55 and that splits the gears.
 
@Rob5589 probably knows for sure, but I'm going to agree with what @pagrey said.

But the question is why would anyone want 3.07 gears? I'm not sure that's a good ratio on any TJ... ever... even bone stock with 29" tires.

Maybe I'm missing something?
 
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X2 to not recommending 3.07 gears for 31" tires. More importantly I would never recommend trying to install used gears, they are a LOT harder to set up than new gears. Even expert gear installers will usually either refuse to install used gears or will charge more due to the significantly greater time required to get them set up. The reason for that is used gears have been work-hardened where they meshed and they would have to be shimmed so they meshed at those same exact locations again... very difficult.
 
Probably be smarter to swap carriers if the goal is to get the "posi." At least that's how I looked at it. I think the answer is the same either way.
 
Carrier break on the 35 is 3.31 and down, 3.55 and up. The 44 is 3.73 & 3.92. It sounds like you want to put your 3.07 into the 3.73 differential. If so, not possible on the 35, possible in 44. But, it will take a full set up, you can't just flip the gears over and be good.
If so, you're looking at gear set up, bearings and seals. As well as someone willing to set up used gears, not always easy to find.
 
pagrey said:
The OP said swap into a 3.73 axle, can't they just swap the carriers?
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If a 44. But he said "Swap the 3.07 gears," so I assume he is talking the gears, not the carrier. Sounds like he has a 3.73 housing with limited slip and wants to put his current 3.07 into it. We'll have to see if he can clarify if he returns.
 
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Gentlemen;

It is a pleasure to be among such learned and technically proficient Jeepers. I thank all of you, especially pagrey, Chris (administrator), and Jerry Bransford, et all.
I appreciate all of your cogent replies and suggestions.
To confirm, presently, my TJ has a non-posi rear with 3:07 gears (oem). Since I do considerable highway driving on the interstate, I thought the high ration would be best for mileage, as I don't go off road. Now, I have an opportunity to purchase a posi axle with 3.73 gears in it. Since mpg remains important, I was going to retain the 3:07 gears and install them in the new 3.73 posi axle. If I'm understanding you all, I can't do this with my Dana 35 axle. I was going to have a mechanic do the swap.
Have I misunderstood any of your replies?

Thanx,
TJTony
 
pagrey said:
Looks like you got it. If you don't go off road I wouldn't worry about the factory "posi" anyway. It isn't that great.
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Pagrey: Thanx for your reply. As you know, the rear end of a TJ is very light and useless in the snow. Plus, I reside on the side of a mountain in Vermont. Typically, I just engage the 4x4 to make the hill. Since I had an opportunity, to purchase a posi for reasonable $$$, I thought that I'd do so. In light of all of the replies, I'm rethinking the purchase.

Regards,
TJTony
 
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TJTony said:
Pagrey: Thanx for your reply. As you know, the rear end of a TJ is very light and useless in the snow. Plus, I reside on the side of a mountain in Vermont. Typically, I just engage the 4x4 to make the hill. Since I had an opportunity, to purchase a posi for reasonable $$$, I thought that I'd do so. In light of all of the replies, I'm rethinking the purchase.

Regards,
TJTony
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Just keep putting it in 4wd. Better control and better traction than 2wd with a very small limited slip unit.

Even if the ls was cheap, you still need to have it set up and most likely, a new bearing set. That "reasonable" purchase price will soon become not so.
 
3.07's are the absolute suck. Most do everything in their power to get rid of them. You're the first I've heard that wanted to install them.
 
TJTony said:
They were oem in my TJ. Since I drive mostly highway miles, I retained them for higher mpg.
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The lowest possible rpms do NOT necessarily improve mpg and in fact can reduce mpg from the engine not operating in its power band. When I regeared from 4.88 to 5.38 to gain more rpms due to the engine lugging (42RLE transmission and 35" tires) two years ago my mpg went from <12 to >14 mpg.
 
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Jerry Bransford said:
The lowest possible rpms do NOT necessarily improve mpg and in fact can reduce mpg from the engine not operating in its power band. When I regeared from 4.88 to 5.38 to gain more rpms due to the engine lugging (42RLE transmission and 35" tires) two years ago my mpg went from <12 to >14 mpg.
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this.

my mileage improved going from 3.73 to 4.56 with my 32's on a 5 speed, moving 70mph from to 2270rpm to 2770.

Going from 3.07 to 3.73 would move your 70mph from 2050 to 2500.

I probably have a few thousand feet of elevation on you, but my TJ wouldn't maintain 65 at 2000rpm even at WOT, using way more fuel than easily maintaining 65 at 30% throttle with a few more rpm.
 
@Rob5589,

The 3;07 gears were oem. Since I do largely highway driving, I retained them for better gas mileage, versus installing a lower ratio 4:10, etc. However, given the replies from this forum, not the least of which is from the TJ Moderator; Jerry Bransford, I'm wondering about the gas mileage issue. I was expecting better gas mileage from larger diameter tires (31"), however, that d/n materialize either. I was told that much larger tires; 33" and up, would result in lower gas mileage due to their increased weight and rolling resistance, but 31s should be fine. My disappointment was exacerbated by the fact that the 6th. gear in the tranny was suppose to be overdrive. All of this aside, my TJ is a soft top and nothing but fun for summer drives to the beach. I wouldn't drive anything else.
 
freedom_in_4low said:
this.

my mileage improved going from 3.73 to 4.56 with my 32's on a 5 speed, moving 70mph from to 2270rpm to 2770.

Going from 3.07 to 3.73 would move your 70mph from 2050 to 2500.

I probably have a few thousand feet of elevation on you, but my TJ wouldn't maintain 65 at 2000rpm even at WOT, using way more fuel than easily maintaining 65 at 30% throttle with a few more rpm.
Click to expand...


Jerry;

My TJ maintains 65 mph effortlessly at considerably less than WOT, UNTIL I start up the mountain (7% grade). Then, I must downshift, as 5th. gear is the only way up. The TJ 6th. gear is less than a 1-1 ratio and only good on level or slight upgrades. Btw, when I installed the 31s, the rpms, at 60mph, dropped to about 1900 rpms,depending on the grade. No change in the gas mileage though. Now I'm wondering if I should consider that 3:73 axle.
 
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