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Old 12-27-2008, 11:00 PM   #1
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Rear Gears

Has anyone swapped out their rearend gears? My Jeep has a 3:23 (?I think) My brother has the exact same Jeep I have and says his has 4:10 gears because he has the tow package.

Can I easily swap for the 4:10's?

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Old 12-27-2008, 11:02 PM   #2
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Yes you can swap them but gear set-up is more suited to be done by a professional.
It's not something for the DIY'er.

But ....You MUST do both front and rear if you use 4wd EVER. This is if your JK is a 4wd.

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Old 12-27-2008, 11:18 PM   #3
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Yes it's a 4WD....I would NEVER, I mean NEVER buy a 2WD Jeep!!!, hahahaha

I would deff. get a shop to do the install.

So....I would need 2 sets of gears? You think by doing this it would give the Jeep a little more "pick me up"?
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Old 12-27-2008, 11:35 PM   #4
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Actually, the gears you have now would be preferred for a quicker take off or "pick-up". Going to some 4.11's will give you a higher top speed, but slow down your take off as there are more teeth to cover/rotate. That is why, when going to a taller tire, you need "taller" gears. If you plan on upping your tire size later on, the 4.11's would be a good idea.
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Old 12-27-2008, 11:40 PM   #5
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^^^ he's got the info there.


But you will need more than just the gears them selves for the front and rear.

Master install kits, Fluids. and your installer.
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Old 12-28-2008, 09:44 AM   #6
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^^^^^^^^^^Great info guys! Thanks for the help. I guess I was just thinking back to the ole' days where we used to put 3:73 or higher gears in the 5.0 Mustangs vs. the stock gears and it gave it alot more pick up. Maybe in the Jeep world it's different
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Old 12-28-2008, 09:57 AM   #7
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umm, i gotta disagree, 4.10''s will make it peppier, but you'll lose on the top end, bigger gears lose speed on the hi end. the driveshaft is turning more times per tire rotation. giving the engine more power off the line, but those increased d shaft turns make the top speed decreased.

just like you said, you put lower gear ratio (higher numerically) in the mustang and its faster off the line, jeeps, and all vehicles will react the same. and you will like the results, its a great upgrade.

it is not cheap though, and make sure the people who do it know what they're doing, not even all mechanics really know how to do it. it requires some special tools only used for this, i have over a grand in tools just to set up gears, most mechanics don't spend the money cuz they don't do it very often.
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Old 12-28-2008, 10:06 AM   #8
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The 4:10 gears only come from the factory with the tow package? This is what my brother has told me........

Or maybe a special order?
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Old 12-28-2008, 10:12 AM   #9
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you can order any set of gears you want. i don't know what axle you have, but 4.88 gears are the biggest for the d35 axle.

go to randy's ring and pinion, or find yukon gears, never had problems with them.
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Old 12-28-2008, 11:59 AM   #10
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i have to agree with jpdocdave, lower gears ex 4.10, 4.88 will give u more low end power and take off at the expence of top speed. rubicons come with the 4.10 stock.
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Old 12-28-2008, 08:57 PM   #11
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It may feel peppy with taller gears, but that is just the torque. There are more teeth in a taller gear, meaning a longer rotation... less speed. You want a smaller gear with a faster rotation for quicker take offs.
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Old 12-28-2008, 09:20 PM   #12
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gears are like a 10 speed bike. keep in mind our legs don't spin at thousands of rpm. you take off on a 10 speed bike in a lower gear. you take off easier, and faster. if you try to take off in 10th gear it is harder and slower. lower gear takes off quicker, but doesn't let you go very fast. 10th gear is hard to take off, but once you get going you can go faster.

lower gears in an axle are the same way, with the more d shaft rotations of a lower gear, just as on a bike, you will take off quicker. obviously axle gears don't shift. so its a balance. when you go to lower gears because of bigger tires, its because the bigger tires actually change the final ratio. a 3.73 gear ratio on stock tires becomes higher with bigger tires. making it more like 3.07. meaning the d shaft is turning closer to 3 times per tire rotation than 4. thus making it slower off the line. when you go to lower gears for bigger tires, you are making the d shaft turn closer to its original ratio. giving you better acceleration.

obviously they won't fit, but you could put a 7 point something gear in an axle, it would take off easily and quickly, but it would go about 40 mph top speed. just like on a 10 speed, first gear lets your legs turn the most times compared to the tire turning. but you can pump your legs till they fall off, but you won't go very fast in first after you take off.

start off in 10th gear and you will barely start moving, but once you keep going you will eventually reach a way higher top speed than the lower gear.
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Old 12-29-2008, 08:09 AM   #13
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I replaced my 3.73's with 4.56's to make towing better, especially on the highway. The tires are slightly larger at a true 32" --- the stock 32's aren't really 32...
It's a totally different (read better) vehicle now. It will get 33's next and that's good enough for me.
It you'll be going to 35's, you'll want 4.88 or 5.13, depending on if you tow. The stock gearing in JK's is a mistake.
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Old 12-29-2008, 07:21 PM   #14
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Quote:
Originally Posted by AzTJ View Post
It may feel peppy with taller gears, but that is just the torque. There are more teeth in a taller gear, meaning a longer rotation... less speed. You want a smaller gear with a faster rotation for quicker take offs.

Back to math class for you


just like on a bike, more teeth on the front is taller gearing, more teeth on the back is lower gearing.. differentials are like the back sprockets.
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Old 12-29-2008, 08:27 PM   #15
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Back to math class for you
easy man, i'm sure you're kidding though. but gears and the way they work are one of the more complicated parts of any vehicle.

numerically higher numbers are lower gears, the way they effect rpm and final drive. the differences in trans, t case and axle all working together, what happens on one end, is lost on the other, and so on. its a hard process to keep straight in your head.

i won't flame anyone for confusing it.
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Old 12-30-2008, 03:29 PM   #16
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3.73 in my stock Sahara which works perfect for my driving and seems to be the perfect compromise.
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Old 12-30-2008, 03:50 PM   #17
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doc has it right and explained it well, but i will give you a dumbed down version:

numerically higher gears are considered "lower".

they need more RPMs to go the same speed,

have more bottom end grunt,

but can hurt mpg, as your engine is spinning faster to go the same speed.

4.10s vs your 3.xx will make it feel like you got a lot more power.


yes, do both front and rear, no, its not really cheap

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