Gears

DROBICON · May 1, 2014

Kinda new to this so I'd like to get people's opinion before I spend the money. I have a 2007 wrangler unlimited 3.8l and I'm looking into getting new gears to get better gas mileage with 35's. My jeep is my daily driver and right now with the 35's I'm getting 10-11 mpg. Was wondering if new gears would give me better gas mileage but not lose a lot of power. Any input is greatly appreciated. Thanks!

OverlanderJK · May 1, 2014

Gears will give you more power and better mileage. If you plan to stay with 35's I'd go 4.88's.

DROBICON · May 1, 2014

OverlanderJK said:
Gears will give you more power and better mileage. If you plan to stay with 35's I'd go 4.88's.

Thanks for the fast reply! How big of a difference do you think? Right now I have 4.10's

Tindeuchen · May 1, 2014

Not sure about the exact numbers on MPG improvements, but there's a chart under the Axles, Gears, and Drivetrain section of this thread that'll show what RPM you can expect at around 70 mph

http://wayalife.com/forumdisplay.php?75-JK-Newbie-FAQ

OBgrnRUBI · May 1, 2014

Larger gears will help your city mpg but won't really help hgwy at all. I have a 08 with 4.10 stock rubi gears and I make 16-17 ave with my 35s on 87 oct. You may need to do a tune up, and possible seafoam your engine to clean it up a little. I was getting 13 with my superchips flashpaq set on performance 93 and running 93 so I switched back to stock and wa-la!

Sent from my SPH-L720 using WAYALIFE mobile app

wayoflife · May 1, 2014

As mentioned, 4.88's will get you back up to stock performance. If you have an auto, you NEED to make sure to properly calibrate your speedometer so that your shift points are correct as well. This will also help with your MPG especially if you do a lot of around town driving.

DROBICON · May 1, 2014

Tindeuchen said:
Not sure about the exact numbers on MPG improvements, but there's a chart under the Axles, Gears, and Drivetrain section of this thread that'll show what RPM you can expect at around 70 mph

http://wayalife.com/forumdisplay.php?75-JK-Newbie-FAQ

Thank you!

DROBICON · May 1, 2014

OBgrnRUBI said:
Larger gears will help your city mpg but won't really help hgwy at all. I have a 08 with 4.10 stock rubi gears and I make 16-17 ave with my 35s on 87 oct. You may need to do a tune up, and possible seafoam your engine to clean it up a little. I was getting 13 with my superchips flashpaq set on performance 93 and running 93 so I switched back to stock and wa-la!

Sent from my SPH-L720 using WAYALIFE mobile app

Thanks for the info!

DROBICON · May 1, 2014

wayoflife said:
As mentioned, 4.88's will get you back up to stock performance. If you have an auto, you NEED to make sure to properly calibrate your speedometer so that your shift points are correct as well. This will also help with your MPG especially if you do a lot of around town driving.

Thank you! I appreciate it!

DROBICON · May 11, 2014

wayoflife said:
As mentioned, 4.88's will get you back up to stock performance. If you have an auto, you NEED to make sure to properly calibrate your speedometer so that your shift points are correct as well. This will also help with your MPG especially if you do a lot of around town driving.

What brand gears do you prefer?

wayoflife · May 11, 2014

Wrangler2174 said:
What brand gears do you prefer?

Doesn't matter being that they are all made by the same South Korean manufacturer and just packaged in different boxes.

DROBICON · May 11, 2014

wayoflife said:
Doesn't matter being that they are all made by the same South Korean manufacturer and just packaged in different boxes.

Awesome. Good to know! Thank you!

jeeeep · May 11, 2014

i have a 2010, went from 4.10 to 4.88 35's the difference was very noticeable.
your mileage depends on how heavy footed you are but I can get 15 around town - sometimes better, freeway 17-20 and as poor as 9 (head on 40mph winds - worst winds I've been in)
too many factors that'll affect mileage

DROBICON · Dec 31, 2014

A friend just told me that you can change just the rear gears and keep the front the same. I have Dana 30 Solid Front Axle and Dana 44 HD Rear Axle. Is this possible?

cozdude · Dec 31, 2014

Wrangler2174 said:
A friend just told me that you can change just the rear gears and keep the front the same. I have Dana 30 Solid Front Axle and Dana 44 HD Rear Axle. Is this possible?

yes BUT you will not be able to use 4wd. its best to just do them both at the same time.

DROBICON · Dec 31, 2014

cozdude said:
yes BUT you will not be able to use 4wd. its best to just do them both at the same time.

Okay thanks man. You're very helpful

Bacon · Dec 31, 2014

Wrangler2174 said:
A friend just told me that you can change just the rear gears and keep the front the same. I have Dana 30 Solid Front Axle and Dana 44 HD Rear Axle. Is this possible?

No. Well, yes technically. You CAN do that, but then you can't put it in 4wd or you'll blow up your transfer case. So the real answer is no you can't. The front and rear outputs of the task need to spin at the same rate or else it will catastrophically fail quite quickly.

07JKSahara · Dec 31, 2014

Wrangler2174 said:
A friend just told me that you can change just the rear gears and keep the front the same. I have Dana 30 Solid Front Axle and Dana 44 HD Rear Axle. Is this possible?

No, if I'm reading that right.... You're front and rear gear ratio MUST be the same. IE, if you run 4.88 in the rear you can not run anything but 4.88 in the front if you EVER plan to use 4wd. The ONLY exception would be if you needed to do it for a day or do to get to the gear shop. Even then, never 4wd.

Edit: wow, you two are fast typers.

DROBICON · Dec 31, 2014

Bacon said:
No. Well, yes technically. You CAN do that, but then you can't put it in 4wd or you'll blow up your transfer case. So the real answer is no you can't. The front and rear outputs of the task need to spin at the same rate or else it will catastrophically fail quite quickly.

That's what I thought thanks!

DROBICON · Dec 31, 2014

07JKSahara said:
No, if I'm reading that right.... You're front and rear gear ratio MUST be the same. IE, if you run 4.88 in the rear you can not run anything but 4.88 in the front if you EVER plan to use 4wd. The ONLY exception would be if you needed to do it for a day or do to get to the gear shop. Even then, never 4wd.

Edit: wow, you two are fast typers.

That's what I thought. I live in NY ya never know when you need 4wd

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