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Old 04-28-2013, 05:14 PM   #1
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33x12.50 do i need to switch gears ?

I have 33x12.50 on 15 inch rims. I dont know if they had the gears changed the jeep is new to me. What would indicate if they have been changed ? Or do i have to take the plate off the pumpkin? ? Would the 33's make 5th gear sluggish ??

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Old 04-28-2013, 05:32 PM   #2
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I have the same set up however I was the one who did the switch.....things that tell you that you need to regear.........
1) Speedo doesn't match GPS!!
2) When taking off from a light in first gear, it is possible to get all the way through the light and still be in first gear whithout the motor screaming at you.
3) When shifting from 4th to 5th and merging with traffic on the highway your jeep slows down.
4) and Lastly...your Jeep doesn't really feel like it is running right unless you are running 70 or better on flat ground with a tail wind...feels as if no power in 5th gear.

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Old 04-28-2013, 05:39 PM   #3
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Well going through the intersection. I shift at 2 or less on the rpms but its almost all the way through. In the wind in fifth its not too bad but its no race car. I know the transfer case was redone or regeared in 08 i have a 99 tj 4.0 manual. On the back of the transfer case it had a circle plate with stamped numbers m/d/y nd it was in 08 so idk
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Old 04-28-2013, 05:58 PM   #4
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It sounds like your differentials probably have stock gears of either 3:07's or 3:73's. There should be a metal tag on the rear end that says what the ratio is. With a 4.0 5 speed with 33" tires, the optimum gear ratio would be 4:56, which means a regear would be a good thing to pursue.
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Old 04-28-2013, 06:01 PM   #5
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Sweet thanks for the info how much does that run ? And ill look at see what it says.
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Old 04-28-2013, 06:02 PM   #6
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This is how you can for sure tell and take the guess work out. Jack the rear tires off the ground enough they can freely rotate. Get under the jeep and turn the drive shaft. Count how many drive shaft rotations it takes for one rotation of the tires. (Note: if only one wheel spins, then count the number of DS rotations for two full rotations if the tire). If it spins about 3 times, you've got 3.07's. If it spins just under 4, you've got 3.73's. If it spins right at/just over 4 turns, you've got 4.10's. About 4.5 turns is 4.56's. And just under 5 turns would indicate 4.88's.

Just curious, you have the the 4.0L or the 2.5L? That'll help narrow it down a bit.
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Old 04-28-2013, 06:07 PM   #7
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Cool ill do that tonight and its a 4.0
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Old 04-28-2013, 06:25 PM   #8
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So as already said, because its a 4.0, you've either got 3.07 or 3.73's most likely. It's possible you have 4.10's though. It was an option for a few years.
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Old 04-28-2013, 08:29 PM   #9
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You need to spin a rear tire precisely two revolutions for the differential to rotate the rear driveshaft the number of times that equals the axle ratio.

If you have a GPS, tell me what your engine RPMs are at 60 mph per the GPS in 5th gear & I can tell you your axle ratio.
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Old 04-28-2013, 08:54 PM   #10
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I did 4.56 gears in my 5sp,4.0 & at 65mph Im at 2500rpm
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Old 04-28-2013, 10:33 PM   #11
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2000Rpm at 60 mph in 5th gear ?
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Old 04-28-2013, 11:53 PM   #12
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If your GPS is showing 60mph in 5th gear and your engine is turning 2000 rpm, looks like 3.73 gears. Don't trust the vehicle speedometer if they didn't change the speedo gear.
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Old 04-29-2013, 12:01 AM   #13
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Ya i think its been changed i went through The speed cameras going five over and it didn't go off and several other school zone radar its right on. So i need 4:56 for it, it looks like $200 or so for the gears and a sat to change them out. Thank ya'll
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Old 04-29-2013, 01:50 AM   #14
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I have 3.73's on 33" and @ 60mph your at the same rpms I am. I have a HUGE dilemma in that, I just bought a 2013 Polaris rzr..its weighs 1000lbs dry and my trailer weighs 700...sooo im working my tranny way way way to hard. After looking on here and talking to a local six states driveline shop, im going to 4.56's. It'll increase my highway ability to keep speed without downshifting every small hill in encounter..towing or not. Also, my gas mileage should improve..will improve with towing. Also, 4:56's give me the ability to go to 35's a little more comfortably and only sacrifice about a 200 rpms difference vs the 600-800 im sacrificing now. A REAL good driveline shop should quote you about $2000-2500. 2500 if they have to change every bearing and seal with the axles itself. I was quoted about 16 hours labor and the rest in parts...they are going factory Dana gears. I was quoted all sorts of prices from a bunch of shops. And yea, I was sticker shocked. But as I have never done gears myself and know I don't have the proper tools to fix handle the lash adjustments and whatnot I feel more comfortable having pro's do it and warranty it. But that's just me! GL keep us posted!
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Old 04-29-2013, 08:02 AM   #15
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Ya ill upgrade to the new gears i need to find a shop and a price. 35s are in mind soon... thanks
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Old 04-29-2013, 09:36 AM   #16
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Quote:
Originally Posted by Robert C. View Post
2000Rpm at 60 mph in 5th gear ?
That calculated out to a 4.10 ratio. A good online calculator is at http://www.manoian.net/jeep/gear_ratio_calculator.html though it doesn't have all the TJ's possible transmissions.
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Old 04-29-2013, 09:52 AM   #17
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Oh ok ill look it up and it might be possible that it is slightly less on rpms i checked again on the way to work and at 60 its just touching 2 grand so idk if its less ir not
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Old 04-29-2013, 02:27 PM   #18
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Originally Posted by Robert C. View Post
Sweet thanks for the info how much does that run ? And ill look at see what it says.

I just had mine changed out from 3.07 to 4.56. I have 33's and the 4.0. I never knew that the gear swap could make so much difference. I absolutely love it. It feels like I've added 100 hp to the engine. It was fun to drive before, but now, wow! Should have done this a long time ago. My cost was around 1800.00, but my old gears were worn out along with the axles, bearings, spiders, so I got the open differential replaced with a LS diff.

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