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Old 08-14-2010, 07:53 AM   #1
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Technical help needed

Ok...I have a 2008 2-dr. 3.8, automatic with 3:73 gears i think. with 33.5s for tires. My problem is in the first two gears when i take off. I have lots of power and torque. But once i get up to cruising speed around 55-60 mph. It falls on its face and is always shifting just to keep up the speed. Is this due to bad gearing? And if so,any suggestions on re-gearing. Oh, i also have a Uni-Chip in place also.

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Old 08-14-2010, 08:29 AM   #2
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Yeah, I'd say thats definitely gearing. Usually the problems don't show up in your power gears but when you get up to cruising or some kind of hill climb like you're saying. I'm new to the jeep scene so I'll let someone else chime in on what gearing to go with or other possible fixes.
From what I've seen, you're just pissing in the wind with chips or other fixes. It'll be cheaper in the long run with less wear and tear on the 3.8 to regear.
What gas mileage are you getting with that setup?

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Old 08-14-2010, 08:40 AM   #3
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I am getting around 15 mpg on a average. Sometimes up to 17 on the highway with a tail wind. i Do have the chip turned off for right now. Im not convinced on the chip thing either. It came with the Jeep.
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Old 08-14-2010, 09:20 AM   #4
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wall98 is correct. when your gears start to get too high from larger tires, OD begins to get elusive.

what's your gear ratio? 33's like to be pushed by 4.10. if your 3.73 you can chip it and be ok. I'm pushing 35's w/a chip on 4.10 (I should be 5.13) and with a little tweaking of my automatic's shift pattern I have almost full use of OD and plenty of giddy up.
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Old 08-14-2010, 09:28 AM   #5
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I've got 4.10 gears and (MEASURED)33.2" Hankook tires, with the auto--

My gearing is RIGHT AT THE EDGE of acceptance for 33" tires/w auto

If you go bigger--need regear !!

I only used the AEV Procal module--no chip, my Rubi operates fine now!!

Good luck

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Old 08-14-2010, 11:30 AM   #6
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So where talking 4:10 gearing? It makes since to me. Now next question is. Is it hard to change the gears out. I am pretty good with tools. But i dont want to get in over my head.
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Old 08-14-2010, 11:34 AM   #7
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If you've never doneit--It's not hard, but


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Originally Posted by castorj29 View Post
So where talking 4:10 gearing? It makes since to me. Now next question is. Is it hard to change the gears out. I am pretty good with tools. But i dont want to get in over my head.
There are tolerant/bushing/torque/clearance measurements and Before/After--

You shouldn't doit--haveit done, because this isn't a comfort mod--it's a drivetrain mod

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Old 08-14-2010, 11:39 AM   #8
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it's very frustrating and time consuming. to the point if my Jeep needed gears, I'd pay the $800 in labor when regears show up at the shop, the mechanics and myself scatter like roaches with the lights on

it requires some shimming, special tools, and patience. you get to the point where you slap an indicator on stuff and tap on things to get it to move .001". that's THOUSANTHS of an inch. .030 is the thickness of a finger nail. I'm a machinist, so a tolerance like that is nothing to me, I've done axles quite a few times, and I still hate it.

if you've never done it, don't. only with an experienced mechanic who has done the job many times, and it takes like all evening to do it. at least me it does
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Old 08-14-2010, 11:40 AM   #9
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Thank Jim........I appreciate your knowledge
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Old 08-14-2010, 11:41 AM   #10
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Thanks Hawg............you guys are the best
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Old 08-14-2010, 12:18 PM   #11
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What's the stock gearing on a standard jk unlimited? I put 33 tires on mine right after I bought it. Am I okay to run that or should I have had the gearing changed?
I'm still a jeep newbie, so I apologize ahead of time for the simple questions. Ha ha
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Old 08-14-2010, 12:37 PM   #12
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if its like mine, you might want to think about
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Old 08-14-2010, 12:46 PM   #13
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Need to know what model unlimited and maybe standard or manual.
For the most part, its a preference thing. From my experience, there is no way that you could miss the fact that you "need" to regear. If you've lost just a little speed you're probably fine and doing no harm to your vehicle. Its all preference.
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Old 08-14-2010, 01:11 PM   #14
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I have a sport auto 2009 unlimited. 17 wheels and 33 tires. I kinda feel I lost a little bit of mpg but it is probably just paranoia.
But I don't even know what that standard gearing is for my model. I do a lot of highway driving weekly and I I could improve the preformance for highway use, it would be nice but not needed. Heck for all I know it's probably not even possible.
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Old 08-14-2010, 01:17 PM   #15
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Quote:
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I have a sport auto 2009 unlimited. 17 wheels and 33 tires. I kinda feel I lost a little bit of mpg but it is probably just paranoia.
But I don't even know what that standard gearing is for my model. I do a lot of highway driving weekly and I I could improve the preformance for highway use, it would be nice but not needed. Heck for all I know it's probably not even possible.
I believe all the autos have 3.73
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Old 08-14-2010, 01:34 PM   #16
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Except the Rubi's and they're, standard 4.10/1


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I believe all the autos have 3.73
I think there's also an option on the other models !!

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Old 08-14-2010, 01:37 PM   #17
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Why are the rubis 4:10? Compared to say mine at 3.73?
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Old 08-14-2010, 01:43 PM   #18
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because the Rubi's have the 4-1 Xfer case and the 4.10/1 diff's is to get the most out of the LOW GEARING !!


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Why are the rubis 4:10? Compared to say mine at 3.73?
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Old 08-14-2010, 01:53 PM   #19
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Any idea how much it would cost to regear a '10 unlimited? Parts & labor.
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Old 08-14-2010, 01:59 PM   #20
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Don't know where you are and it varies all over

Figure $800 to 1800 bucks !!

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Old 08-14-2010, 02:05 PM   #21
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Thanks Jimbox, I am i the Atlanta area. How would the regear affect highway speeds. I am running 35's with a 6sp manual. What would you suggest? The 5.13? Thanks!
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Old 08-14-2010, 02:08 PM   #22
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can't tell you much more, somebody who has the 4.88 or 5.13 and 6spd. will have to join in--


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Thanks Jimbox, I am i the Atlanta area. How would the regear affect highway speeds. I am running 35's with a 6sp manual. What would you suggest? The 5.13? Thanks!
I've got Rubi with auto and 4.10 and 33.2" tires and Im content !!

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Old 08-14-2010, 02:16 PM   #23
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I couldn't imagine going above 4.88s with a manual transmission on a rig that sees the highway.
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Old 08-14-2010, 04:43 PM   #24
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I half wonder if chrysler decided on 4.10's in the rubi to compensate for the larger 32" tires as well as the 4to1 transfer case.

With the four door it does ok stock without it being weighed down. It seems more to be a tranny programming and throttle calibration issue to me that causes the highway driving issues when weighed down and in general. I am trying to decide on a 33s or 35s as well. I will be running the superchips and if I'm not happy I will switch to diablo and get a custom tune written. I still wonder even then what it is going to drive like. I can deal with a little highway sluggishness as long as I retain good offroad performance. That is why my heart says 35s but my brain says go with a tall 33 like what JIMBOX runs.

Hard to judge based off of internet opinions because different people drive different. Different weights are involved most likely. Different gears,2 vs 4 door, auto vs manual. A guy almost just has to take the dive and do what he wants and accept that he might have to pay for the consequences.
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Old 08-14-2010, 04:56 PM   #25
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Good points


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I half wonder if chrysler decided on 4.10's in the rubi to compensate for the larger 32" tires as well as the 4to1 transfer case.

With the four door it does ok stock without it being weighed down. It seems more to be a tranny programming and throttle calibration issue to me that causes the highway driving issues when weighed down and in general. I am trying to decide on a 33s or 35s as well. I will be running the superchips and if I'm not happy I will switch to diablo and get a custom tune written. I still wonder even then what it is going to drive like. I can deal with a little highway sluggishness as long as I retain good offroad performance. That is why my heart says 35s but my brain says go with a tall 33 like what JIMBOX runs.

Hard to judge based off of internet opinions because different people drive different. Different weights are involved most likely. Different gears,2 vs 4 door, auto vs manual. A guy almost just has to take the dive and do what he wants and accept that he might have to pay for the consequences.

Thats why, I choose the Hankooks, one of the FEW tires that are ACTUALLY 33" INSTALLED and based on past history a 2.5" lift, so my driveshafts and pinion angles and Universals would be relatively "unaffected" !!

Now-when you immediately jump to 35" tires (I don't know why) then you start having real clearance/univ./shock/swaybar/diff gear-PROBLEMS

I'm afraid that the majority of NEW JEEPERS THINK that --

It's not a REAL JEEP, unless it has 35" tires/winch/overhead lights/snorkel--onit

Ah well, it's a jungle out there !!

Good day

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Old 08-14-2010, 05:14 PM   #26
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Quote:
Originally Posted by JIMBOX View Post
Good points





Thats why, I choose the Hankooks, one of the FEW tires that are ACTUALLY 33" INSTALLED and based on past history a 2.5" lift, so my driveshafts and pinion angles and Universals would be relatively "unaffected" !!

Now-when you immediately jump to 35" tires (I don't know why) then you start having real clearance/univ./shock/swaybar/diff gear-PROBLEMS

I'm afraid that the majority of NEW JEEPERS THINK that --

It's not a REAL JEEP, unless it has 35" tires/winch/overhead lights/snorkel--onit

Ah well, it's a jungle out there !!

Good day

JIMBO
I agree. Some folks want 35's for less than sane reasons. I think your setup looks great. No need to go bigger and haul around more weight than you need to.

I am going a little higher than you and with flat flares so it would most likely make the same 33's your running look smaller. Not by much though. I do care about looks but performance is paramount. I will be running 32's for awhile with the lift and flares so that might help decide. The more I talk about it the more I lean to the 33's.

Weight for me is a constant concern. This is my wifes daily driver. However we wheel it all the time. For normal day wheeling trips I am not as concerned with weight because we are only packing recovery gear for the most part. We do a ton of camping too far from home. We pack heavy for that and a lot of times bring a chase truck to camp with even more gear. I also have a winch and steel bumpers going on as well as heavy skid plates because I use the jeep smart but hard. Those items are not for show. No snorkel because I never plan on going that deep. Every time I think of a mod I do think of weight. My rig just keeps getting heavier. Plan on towing a trailer soon too. I just have to accept the fact that It's gonna be one fat, heavy girl. Might have to pay the piper with gears and or a hemi conversion down the road.

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