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Hey wondering what people have been regearing their 3.8L dog of an engine in the 2007 4 door sahara Automatic to after putting larger tires on. The 3.8 was a dog even at stock but after putting 33" tires its really a dog now. I've seen 5.13 recommended on some sites but wondering what others have and how they like it.


Thanks!
 

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2007 2 dr manual tranny went to 4.56 gears and 33's tried 35's didn't like them. Like my setup. 4.88's would probably work good for you having an auto.
 

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Hey wondering what people have been regearing their 3.8L dog of an engine in the 2007 4 door sahara Automatic to after putting larger tires on. The 3.8 was a dog even at stock but after putting 33" tires its really a dog now. I've seen 5.13 recommended on some sites but wondering what others have and how they like it.


Thanks!

What is your long term goal? DD?
 

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No, I have other vehicles for a daily driver. I would like it to be able to handle highway speeds (70 mph) and not struggle to get there though.
With that set up and wanting passing power on highways you would not want to go less than 5.13's, but if you think that you will do more off-roading and possibly go up even one size in tires your long term bet should be on 5.38's.

Your chart (automatic);
38gears.jpg

Either will be okay to drive regularly, but the 5.38's might eat a little more gas while on 33's.

Jeff B.
 

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Are you going to stick with the 33's or are you looking to go bigger?

Another note is make SURE you do the gears with the Master install kit. This will get you all new bearings and everything. The way to go when you do new gears! We also recommend and do a ton of the Revolution Gear and Axle line:
https://www.krawloff-road.com/REVOLUTION_GEAR_AND_AXLE_s/2208.htm

If we can help, please let us know!

-Jason
 

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Discussion Starter #8
With that set up and wanting passing power on highways you would not want to go less than 5.13's, but if you think that you will do more off-roading and possibly go up even one size in tires your long term bet should be on 5.38's.
So at the higher gearing, (at a set speed) you're just running higher RPMs right?
 

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Higher gear ratio number means shorter gearing which means more rpms (and power) at a given mph speed.
When you replace tires with larger tires you change the overall gear ration as the diameter of the tires is part of that equation. Re-gearing with a higher number gear ration can bring the overall gear ratio back to where it started or even further to deliver more power at the tires.
The older 3.8 motor with the old auto trans needs all the help it can get, especially with bigger than stock tires. I would think re-gearing to around 4.88 gears would be good for 33" tires. But if you live at higher elevations and / or tow a lot you might want to go further.
 

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Higher gear ratio number means shorter gearing which means more rpms (and power) at a given mph speed.
When you replace tires with larger tires you change the overall gear ration as the diameter of the tires is part of that equation. Re-gearing with a higher number gear ration can bring the overall gear ratio back to where it started or even further to deliver more power at the tires.
The older 3.8 motor with the old auto trans needs all the help it can get, especially with bigger than stock tires. I would think re-gearing to around 4.88 gears would be good for 33" tires. But if you live at higher elevations and / or tow a lot you might want to go further.
He's in the 3.8 not 3.6L and he said its not his daily driver.. 4.88 not deep enough...IMO
 

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He's in the 3.8 not 3.6L and he said its not his daily driver.. 4.88 not deep enough...IMO
Right, 3.8, auto trans, and 33" tires. 4.88 gears is a common option for that. But sure, he can go further, as mentioned. But with a D30 up front I would not go past 5.13 gears.
 

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Right, 3.8, auto trans, and 33" tires. 4.88 gears is a common option for that. But sure, he can go further, as mentioned. But with a D30 up front I would not go past 5.13 gears.
You're spot on with that call.. If the D30 is up front, the D30 gears are going to thin out considerably at 4.88.

Addendum:

You need to upgrade the front axle to a D44 :thumb:
 

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Discussion Starter #13
Right, 3.8, auto trans, and 33" tires. 4.88 gears is a common option for that. But sure, he can go further, as mentioned. But with a D30 up front I would not go past 5.13 gears.
Oh interesting, why would the D30 limit the gear ratio?
... Nevermind... just saw the above response...

thanks!
 

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Oh interesting, why would the D30 limit the gear ratio?
... Nevermind... just saw the above response...

thanks!
To try to explain it further, the gear set on a D30 is smaller than the gear set on a D44 for the same ratio. So at a 4.88 or 5.13 gear set the pinion gear is getting pretty small. As you go to a higher number gear ration the pinion gear gets smaller. That means that there is less gear tooth contact at any given time. So it means the gear set is weaker, so most try to stay at a max of 4.88 or 5.13 gears with the D30.
Personally, I don't think you need a new axle, but I would stay at 4.88 or 5.13 gears as a max. 4.88 gears for 33" tires should be middle of the road good. If you want more torque / power at the wheels, go with 5.13 gears. But I would not go further than that with the D30.
 

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Discussion Starter #15
To try to explain it further, the gear set on a D30 is smaller than the gear set on a D44 for the same ratio. So at a 4.88 or 5.13 gear set the pinion gear is getting pretty small. As you go to a higher number gear ration the pinion gear gets smaller. That means that there is less gear tooth contact at any given time. So it means the gear set is weaker, so most try to stay at a max of 4.88 or 5.13 gears with the D30.
Personally, I don't think you need a new axle, but I would stay at 4.88 or 5.13 gears as a max. 4.88 gears for 33" tires should be middle of the road good. If you want more torque / power at the wheels, go with 5.13 gears. But I would not go further than that with the D30.
I think I just need a new engine... That would solve my problem! lol

Thanks a lot for the info. Yeah, not quite ready to throw $4k at a new axle so I'll stick with the 4.88. I dont think I'll be doing any larger that 33" Tires anyways. How much does re-gearing usually cost? I was guessing around $1500?
 

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I think I just need a new engine... That would solve my problem! lol

Thanks a lot for the info. Yeah, not quite ready to throw $4k at a new axle so I'll stick with the 4.88. I dont think I'll be doing any larger that 33" Tires anyways. How much does re-gearing usually cost? I was guessing around $1500?
It seems to depend on the area you live in. $1500 is about average, but some areas are lower while many are higher. Around here it runs closer to $1800. But re-gearing is a great time to upgrade your diffs to either lockers or limited slips. That can increase the cost, but at a minimum I would add a mechanical limited slip in the rear like a TrueTrac. I have a TrueTrac in the rear and a locker in the front. But the original plan was to go with TrueTracs front and rear. That is what my sister in-law went with and it works really well. But we ended up swapping to a D44 out of a Rubicon up front and it came with the stock e-locker. In the end it works fine, but I still kinda wish I had TrueTracs front and rear.
 

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I think I just need a new engine... That would solve my problem! lol

Thanks a lot for the info. Yeah, not quite ready to throw $4k at a new axle so I'll stick with the 4.88. I dont think I'll be doing any larger that 33" Tires anyways. How much does re-gearing usually cost? I was guessing around $1500?
What part of the country are you in???

I just had mine done for $800 by a rock star custom shop.
 

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What part of the country are you in???

I just had mine done for $800 by a rock star custom shop.
Haha I live in Washington State... it was a total WAG. I have no idea... I was just going off quotes I've gotten for other stuff.

$800 aint bad at all!
 

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Never heard of it and I wouldn't trust it.. A lot of products that come out of foreign countries, made of steel, just don't add up to USA made steel.
I would stick with American made:
Spicer (i'm using now)
G2(I've used previously)
maybe Yukon
If you need a connect, you can call Joe Cruz @ Morris4x4. He's very fair.

You don't have to pay a fortune, but you don't want budget gears either.. not if you expect them to last. IMO
 
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