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Discussion Starter #1
Sorry accidentally deleted my prior post. So I regeared my 2010 jk 3.8 auto with 3.73s to 4.56s. Was told I did not need to program the pcm by the shop - a couple on here (sorry for the delete - lol) replies. Thank you. I’m still getting some saying it needs done and some saying if a model prior to 2012 there is no need to do so. I just don’t want to tear up my engine or trans due to rpms/shifting issues. I just got it back today from the shop and haven’t really had a chance to test it out fully yet. Anymore feedback is always welcome. anyone else on here have the regear done and yours is a older pre-2012 year? Thanks gang.
 

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^ what he said ...

do you need it ? no, if you don't care about speedo,rpms & mileage accuracy
will it be better to use tuner on it? yes.

 

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The 42RLE doesn't need to know about a change in ring/pinion ratio.

2012+ autos do need to be reprogrammed because of the lack of internal input/output rpm sensors.

A change in ring/pinion ratio won't change speedometer accuracy.
 

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The 42RLE doesn't need to know about a change in ring/pinion ratio.

2012+ autos do need to be reprogrammed because of the lack of internal input/output rpm sensors.

A change in ring/pinion ratio won't change speedometer accuracy.
Your first 2 sentences are correct.
The last one you are wrong. Think about it. The Speedo gets it signal from the output shaft of the transmission. You go to a higher gear ratio the output shaft is going to spin faster to go the same speed, thus showing a fast mph.
But he added 33inch tires without a gear change so the Speedo was showing him going slower than he actually was. Now he adding the 456 gears he might be back in the ball park of his actual mph.

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Your first 2 sentences are correct.
The last one you are wrong. Think about it. The Speedo gets it signal from the output shaft of the transmission. You go to a higher gear ratio the output shaft is going to spin faster to go the same speed, thus showing a fast mph.
But he added 33inch tires without a gear change so the Speedo was showing him going slower than he actually was. Now he adding the 456 gears he might be back in the ball park of his actual mph.

Sent from my LM-V405 using Tapatalk
I think the 2012+ units get the speed input from the wheel sensors, thus changing the gears has no effect.
 

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I think the 2012+ units get the speed input from the wheel sensors, thus changing the gears has no effect.
The vehicle in question is a 2010.
Yes the wheels have speed sensors but they are used for the braking system. Your actual speed is read off of your transmission speed sensors.

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Discussion Starter #8
Sorry accidentally deleted my prior post. So I regeared my 2010 jk 3.8 auto with 3.73s to 4.56s. Was told I did not need to program the pcm by the shop - a couple on here (sorry for the delete - lol) replies. Thank you. I’m still getting some saying it needs done and some saying if a model prior to 2012 there is no need to do so. I just don’t want to tear up my engine or trans due to rpms/shifting issues. I just got it back today from the shop and haven’t really had a chance to test it out fully yet. Anymore feedback is always welcome. anyone else on here have the regear done and yours is a older pre-2012 year? Thanks gang.
Update: This is the information I’ve been looking for and appreciate all the input and feedback. I double checked my programmer (JScan) to ensure proper tire size (285s) 33s actually measuring 32” so that is correct. Before messing with the axle ratio setting I took it for a spin. Previously it would down shift in the slightest headwind or going up the slightest of hills. (Steel bumpers, winch, rock sliders, hardtop, full doors, etc) I had no issue whatsoever ever with the overdrive in the on position! Went up a somewhat steep grade at 45mph without having to push the OD button! No limp mode and my gps app shows correct speed. So I’m assuming the articles I’ve been reading that if the JK is prior to 2012 with an auto (which mine is) then a flash to update the ratio isn’t needed in my instance. 👌. Rpms/speed are fine, shifting feels smooth and accurate and no down shifting! I’ll drive as is for now until my gears are broke in and will post updates if I end up trying to do the flash.
 

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Discussion Starter #9
Thank you. Yeah, I’m not in limp mode and since I’ve flashed for my tire size already, everything appears to be “happy”! 4.56 install with tire size update appears all that was needed.!thank you sir.


The 42RLE doesn't need to know about a change in ring/pinion ratio.

2012+ autos do need to be reprogrammed because of the lack of internal input/output rpm sensors.

A change in ring/pinion ratio won't change speedometer accuracy.
 

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Addressing some posts above...

The JKs, early and late, get speedometer and odometer input from the wheel speed sensors. There is no tail shaft sensor.

The 2012+ auto transmissions have no internal primary and secondary rpm sensors, so they depend on wheel speed sensor data to calculate its internal secondary rpm, thereby making it essential the pcm has correct tire size and gear ratio. Primary rpm is taken from the engine rpm.

The pre-2012 auto transmissions have internal primary and secondary speed sensors, making ring/pinion ratio data unnecessary.
 

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Discussion Starter #11
Addressing some posts above...

The JKs, early and late, get speedometer and odometer input from the wheel speed sensors. There is no tail shaft sensor.

The 2012+ auto transmissions have no internal primary and secondary rpm sensors, so they depend on wheel speed sensor data to calculate its internal secondary rpm, thereby making it essential the pcm has correct tire size and gear ratio. Primary rpm is taken from the engine rpm.

The pre-2012 auto transmissions have internal primary and secondary speed sensors, making ring/pinion ratio data unnecessary.
👍 Thanks again. 👋🔘|||||||🔘
 

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Discussion Starter #12
So there is no need to be concerned about the transmission and transfer case working Properly together then correct? I would assume this we be fine...but just asking. I believe there is nothing else I need to do or be concerned about other than draining my diff fluid after 500 miles and checking the wear and refilling.


Addressing some posts above...

The JKs, early and late, get speedometer and odometer input from the wheel speed sensors. There is no tail shaft sensor.

The 2012+ auto transmissions have no internal primary and secondary rpm sensors, so they depend on wheel speed sensor data to calculate its internal secondary rpm, thereby making it essential the pcm has correct tire size and gear ratio. Primary rpm is taken from the engine rpm.

The pre-2012 auto transmissions have internal primary and secondary speed sensors, making ring/pinion ratio data unnecessary.
 

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So there is no need to be concerned about the transmission and transfer case working Properly together then correct? I would assume this we be fine...but just asking. I believe there is nothing else I need to do or be concerned about other than draining my diff fluid after 500 miles and checking the wear and refilling.
That is correct.

Lots of people with the early JK auto transmissions have been fine with not needing to reprogram for a gear ratio change.

As soon as the 2012 JKs came out, people were finding the transmission would go into limp mode when they changed gear ratios without reprogramming.
 

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Discussion Starter #14
So there is no need to be concerned about the transmission and transfer case working Properly together then correct? I would assume this we be fine...but just asking. I believe there is nothing else I need to do or be concerned about other than draining my diff fluid after 500 miles and checking the wear and refilling.
That is correct.

Lots of people with the early JK auto transmissions have been fine with not needing to reprogram for a gear ratio change.

As soon as the 2012 JKs came out, people were finding the transmission would go into limp mode when they changed gear ratios without reprogramming.
👍 I really appreciate your information and guidance! I’ve been wanting to regear for the last 3-4 years and finally got it done! Again...you’ve been extremely helpful!
 

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if you ever decide you need a tuner, i have a Superchip Flashpag 3875 ill let go for super cheap.
 

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I have an '09 JKUR that runs 5:38 gears and 37s. I reprogrammed both gear ratio and actual tire diameter years ago with an AEV Procal. You should do the same. Doing so corrected the shift points and the speedometer is dead on the money as tracked with a GPS. Procals aren't tuners, they just reset for gears & tire size and have a few other useful features, such as shutting off the stupid sway bar light after you throw that electro-fail POS in the trash, centering the steering wheel via the sensor, and using the dash light illumination switch to increase RPM at idle (winching, etc.). Worth the money.
 
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Have a 2010 JKU and just changed from 3.73 to 5.13...can confirm my speedo is just as off as it was before...runnings 37s without programming
 

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Hi. I’m running on 265/70 R17 (31.6 inches) and I feel (automatic) box like hesitates when it comes to driving at more than 120 per hour. Or it is high (more than 3.5x1000) and the speed is increasing or it is low (less than 2X1000) and the speed is decreasing. It is impossible to maintain a regular RMP / speed. GM decreased drastically. Do you think I have to regear? Do the Barricade roof rack have something to do with that? Thank you


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Your first 2 sentences are correct.
The last one you are wrong. Think about it. The Speedo gets it signal from the output shaft of the transmission. You go to a higher gear ratio the output shaft is going to spin faster to go the same speed, thus showing a fast mph.
But he added 33inch tires without a gear change so the Speedo was showing him going slower than he actually was. Now he adding the 456 gears he might be back in the ball park of his actual mph.

Sent from my LM-V405 using Tapatalk
I thought I was a troll. You win!
Unless you think you actually know wtf you are talking about.
 
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