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Old 03-29-2012, 07:59 PM   #1
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Question JK rear end questions?

I have a jk with a stock rear end dana 44 and just put on a set of 35X12.5R18 just wondering if i need to change the gears in the end or will I be ok with what I have?

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Old 03-29-2012, 08:03 PM   #2
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You'll know after driving it for a while. If it feels like a slug, you need to re-gear. BTW, you need to do the front as well.

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Old 03-29-2012, 08:09 PM   #3
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Any ideas on what I should change to? I got this jk bone stock so I could change everything out but not to extreme that I cant use it as a daily driver.
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Old 03-29-2012, 08:23 PM   #4
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Drive it for a while and read everything you can on this forum. Everything is dependent on your tranny, the year of your Jeep, and your current gears.
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Old 03-29-2012, 10:07 PM   #5
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Quote:
Originally Posted by wmwhitey View Post
I have a jk with a stock rear end dana 44 and just put on a set of 35X12.5R18 just wondering if i need to change the gears in the end or will I be ok with what I have?
Give up some details of what you have; stick, auto, year.. Do you know your current gears?
edit: Yeah, like Bert said.

Chew on this a little bit:
Gear Ratio Calculator

The Wolfman will be along shortly. He has educated himself quite well in this area.

I'll check back later to see how it's going. I'm in this self educating mode myself.
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Old 03-29-2012, 10:13 PM   #6
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I have a 2010 jk 2 door sport manual trans and i dont know the gear ratio.
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Old 03-29-2012, 10:52 PM   #7
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I have a 2010 jk 2 door sport manual trans and i dont know the gear ratio.
Somewhere out there is a site you can get your build sheet from your VIN. Sorry I don't ahve the link. When you go down the highway at 60 is your tach running about 1600 in 6th gear? Do you hate seeing a slight hill coming up ahead? Do 18-wheelers regularly pass you by? How about if you get a piece of gum on your tire does it come to a near stand-still? I suspect you are running 3.21 gears; just a guess. That's what I got and I plan to go to 4.88.

So if you answered yes to any of those questions you might want to try this; stop shifting once you get to 4th gear. Maybe 5th, depending on what you have. My jeep hasn't seen 5th or 6th in about a month and I love the way it drives. I can compete on the highway now. I use cruise control and don't worry about the hills anymore. I can ease around slower cars or "18-wheelers" without problems. My rpm runs about 2500 on the highway at about 62 and maybe I lost about 1mpg.

I can't wait to regear. Just waiting on funding. I expect first gear won't be use so much. But won't it be great for crawling. Shifting all the way to 6th will make driving much more fun.

If you ahven't gotten some links to a ton of info by tomorrow I will find some and point you in the right direction. Now i got to regenerate for another work day.
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Old 03-30-2012, 09:47 AM   #8
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Yes, you will benefit from a re-gear. If you have a Sport your gear ratio will be either 3.21 or 3.73, both of which are too tall of a gear for 35" tires. If it were a Rubicon with 4.10 gear ratio you could probably live with it being a manual transmission. The automatic transmission is out of the question.

I am sure once you get the mechanical leverage back that you lost from the larger tires/wheels you will be much more happy with the performance. Also keep in mind that with larger tires/wheels usually comes a lift kit which now changes the frontal area of the Jeep and increases drag and if you are like most of us you are also adding weight from bumpers, winches, skids and tools this all adds weight which compounds the performance loss.

For the manual transmission with 35" tires I would recommend 4.88 gears.

Also, your thread is titled "JK rear end questions", just keep in mind you have to change the gears in the front axle as well.

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Old 03-30-2012, 10:34 AM   #9
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You'll probably want 4.88 or 5.13 for your manual 3.8L. You have to do both axles and the gears will run you about under $600 shipped for the R&P and the master install kits. YOu may want to strenghten your fron axle too with at least some inner c-gussets from Poly Performance.

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Old 03-30-2012, 10:51 AM   #10
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Dang, and I thought I was just about "Done" with my mods....at least for a while.

The good news is that I get to work on it again (it has been a week after all).
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Old 03-30-2012, 10:54 AM   #11
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Old 03-30-2012, 12:50 PM   #12
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I've researched this quite a lot and based on the information I've gathered you want atleast 4.88's with 35's.

I've got a 09 2dr auto trans Rubicon with stock 4.10's and with only the 33's I'm running the road has to be flat with no hills or I have to take it out of OD. I will never go bigger than 33's and when/if I ever change gears they will be 4.88's
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Old 03-30-2012, 02:19 PM   #13
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Thank you all for the help I get the jeep out of the shop today but it looks like it will be getting new gears soon also. SO THE question I have Is what gears should i got to living here in hawaii lots of hills.
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Old 03-30-2012, 02:34 PM   #14
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4.88 preferrably with your manual trans but if you may ever want to go 37's then do the 5.13's now.

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Old 03-30-2012, 03:04 PM   #15
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Can someone explain to me, the best way to get my stock performance back, starting from cheapest to more expensive mods available, programing, intake, gears, I currently run a 3" bds, lift with 35" tires, on a 2009 jk 2 dr, with 3.75 gears 3.8L, auto trans.

Thanks in advance
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Old 03-30-2012, 03:20 PM   #16
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Quote:
Originally Posted by Rick8240
Can someone explain to me, the best way to get my stock performance back, starting from cheapest to more expensive mods available, programing, intake, gears, I currently run a 3" bds, lift with 35" tires, on a 2009 jk 2 dr, with 3.75 gears 3.8L, auto trans.

Thanks in advance
Superchips Flashpaq
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Old 03-30-2012, 03:59 PM   #17
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Quote:
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Can someone explain to me, the best way to get my stock performance back, starting from cheapest to more expensive mods available, programing, intake, gears, I currently run a 3" bds, lift with 35" tires, on a 2009 jk 2 dr, with 3.75 gears 3.8L, auto trans.

Thanks in advance
When you say the cheapest way to get your stock performance back it is a bit of a convoluted question. The only way to get your stock performance back is gearing. That is what changed from stock when you went with larger tires/wheels.

You cannot magically get back to stock by adding performance enhancers such as a tuner and a cold air intake and exhaust will do minimal on the 3.8 Jeep which is a speed density system. The best of both worlds would be to get the gear ratio correct and then add a tuner. The tuner should give you an increase of approx. 25 HP.

The automatic equiped Jeeps have an even bigger problem in that they came from the factory incorrectly geared. The automatic should have come equiped w/ 4.88 and the 32" tires. If you have 35" tires I would recommend 5.38 gears if you have the d44 (Rubicon) or 5.13 if you have a Sahara or Sport with the d30 front axle.

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Old 03-30-2012, 04:12 PM   #18
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Kinda agree with ya, except the 3.8 and auto/w 5.38 gears-


Quote:
Originally Posted by zmotorsports View Post
When you say the cheapest way to get your stock performance back it is a bit of a convoluted question. The only way to get your stock performance back is gearing. That is what changed from stock when you went with larger tires/wheels.

You cannot magically get back to stock by adding performance enhancers such as a tuner and a cold air intake and exhaust will do minimal on the 3.8 Jeep which is a speed density system. The best of both worlds would be to get the gear ratio correct and then add a tuner. The tuner should give you an increase of approx. 25 HP.

The automatic equiped Jeeps have an even bigger problem in that they came from the factory incorrectly geared. The automatic should have come equiped w/ 4.88 and the 32" tires. If you have 35" tires I would recommend 5.38 gears if you have the d44 (Rubicon) or 5.13 if you have a Sahara or Sport with the d30 front axle.

Mike.
It"s beneficial for the JKU, for any size tire above 32", except tires above 35", then for optimum ops-

You'll need to switch to Dana 60s and diff. ratios in the 6.xx range !

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Old 03-30-2012, 04:57 PM   #19
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I have a 2010 sport that had the 3:21gears. After driving it for almost a year with a 3" lift & 35's I installed 4:88 gears what a difference. Best mod. yet ! You will not regret the gear change.
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Old 03-30-2012, 05:23 PM   #20
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Quote:
Originally Posted by zmotorsports View Post
When you say the cheapest way to get your stock performance back it is a bit of a convoluted question. The only way to get your stock performance back is gearing. That is what changed from stock when you went with larger tires/wheels.

You cannot magically get back to stock by adding performance enhancers such as a tuner and a cold air intake and exhaust will do minimal on the 3.8 Jeep which is a speed density system. The best of both worlds would be to get the gear ratio correct and then add a tuner. The tuner should give you an increase of approx. 25 HP.

The automatic equiped Jeeps have an even bigger problem in that they came from the factory incorrectly geared. The automatic should have come equiped w/ 4.88 and the 32" tires. If you have 35" tires I would recommend 5.38 gears if you have the d44 (Rubicon) or 5.13 if you have a Sahara or Sport with the d30 front axle.

Mike.
One R&P manufacturer does make 5.38's for the D30. I think it is Richmond and are now owned or distributed by a company called Just Differentials.(?) I was going to go with 5.38's but with only one shop manufacturing them and one vendor distributing them, I ultimately went with 5.13's.

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Old 03-30-2012, 06:35 PM   #21
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thanks for the info just got the jeep out the shop and it feels ok but I need to drive it more the lift and tires look good.
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Old 03-30-2012, 06:36 PM   #22
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the lift and tires just got done today
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Old 03-30-2012, 07:06 PM   #23
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Looks pretty good, but the front seems much higher than the back--

Do you plan on a new bumper/winch ??

That weight would probably levelit, without going back into the suspension !

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Old 03-30-2012, 07:18 PM   #24
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very nice! Jimbo... looks like it might be a slight rise in the driveway or something...
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Old 03-30-2012, 07:18 PM   #25
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Quote:
Originally Posted by jimbox
:d looks pretty good, but the front seems much higher than the back--

do you plan on a new bumper/winch ??

That weight would probably levelit, without going back into the suspension !

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Old 03-30-2012, 08:52 PM   #26
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the Driveway does have a slant and yes I have a smittybily stinger on the way for it with a 10k winch
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Old 03-30-2012, 09:04 PM   #27
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----BINGO---


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the Driveway does have a slant and yes I have a smittybily stinger on the way for it with a 10k winch
It'll be AOK !

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Old 03-31-2012, 01:48 AM   #28
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Quote:
Originally Posted by zmotorsports

When you say the cheapest way to get your stock performance back it is a bit of a convoluted question. The only way to get your stock performance back is gearing. That is what changed from stock when you went with larger tires/wheels.

You cannot magically get back to stock by adding performance enhancers such as a tuner and a cold air intake and exhaust will do minimal on the 3.8 Jeep which is a speed density system. The best of both worlds would be to get the gear ratio correct and then add a tuner. The tuner should give you an increase of approx. 25 HP.

The automatic equiped Jeeps have an even bigger problem in that they came from the factory incorrectly geared. The automatic should have come equiped w/ 4.88 and the 32" tires. If you have 35" tires I would recommend 5.38 gears if you have the d44 (Rubicon) or 5.13 if you have a Sahara or Sport with the d30 front axle.

Mike.
Guys great info, so I guess with my particular setup your recommending 5.13, is there any draw back, like fuel issues, with gas prices the way they are, I wanna be able to enjoy my ride and not kill my pocket at the same time
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Old 03-31-2012, 10:19 AM   #29
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Just remember, that to change your diff gears --JUST FOR MILEAGE is rather ludicrous--

You will immediately start driving different and your mileage may not get better--

The cost of regearing, may be as high as 2000 bucks----------you may have to drive for 5 to 10 YEARS at a GRANDMA pace--to scientifically realize a balance of profit/loss-

Usually we change the ratio for PERFORMANCE--and maybe the mileage will improve, but probably not !!

Good luck

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Old 03-31-2012, 10:45 AM   #30
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Ok so if I don't regear, is the added weight of the tires and bumper , putting a strain on my tranny in anyway, I don't wanna regear unless it's beneficial to the wear and tear of my vehicle

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