Regear question - JKowners.com : Jeep Wrangler JK Forum
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post #1 of 15 Old 02-13-2020, 04:22 PM Thread Starter
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Regear question

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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post #2 of 15 Old 02-13-2020, 06:10 PM
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a programmer will be beneficial to you. It will correct your speedometer and odometer and adjust your shift points where they should be.
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post #3 of 15 Old 02-14-2020, 05:36 AM
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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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post #4 of 15 Old 02-14-2020, 06:49 AM
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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.

2008 Unlimited Rubicon Automatic

Last edited by ronjenx; 02-14-2020 at 06:52 AM.
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post #5 of 15 Old 02-14-2020, 09:01 AM
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Quote:
Originally Posted by ronjenx View Post
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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post #6 of 15 Old 02-14-2020, 09:12 AM
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Quote:
Originally Posted by rich6700 View Post
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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I think the 2012+ units get the speed input from the wheel sensors, thus changing the gears has no effect.

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post #7 of 15 Old 02-14-2020, 09:19 AM
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Originally Posted by Guruman View Post
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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post #8 of 15 Old 02-14-2020, 11:16 AM Thread Starter
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Originally Posted by 2BJPN View Post
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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post #9 of 15 Old 02-14-2020, 11:27 AM Thread Starter
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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.


Quote:
Originally Posted by ronjenx View Post
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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post #10 of 15 Old 02-14-2020, 02:19 PM
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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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post #11 of 15 Old 02-14-2020, 02:47 PM Thread Starter
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Quote:
Originally Posted by ronjenx View Post
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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post #12 of 15 Old 02-14-2020, 03:02 PM Thread Starter
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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.


Quote:
Originally Posted by ronjenx View Post
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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post #13 of 15 Old 02-14-2020, 03:21 PM
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Originally Posted by 2BJPN View Post
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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post #14 of 15 Old 02-14-2020, 03:46 PM Thread Starter
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Quote:
Originally Posted by ronjenx View Post
Quote:
Originally Posted by 2BJPN View Post
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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post #15 of 15 Old Today, 10:27 AM
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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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