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Discussion Starter #1
Hey guys I have seen many questions over the last couple years about converting to LSD in the 15+ Chargers. I have the Road and Track package with 230mm axles. I just swapped out my open 3.07 to a 3.90 with no issues whatsoever. I didn't even need to reprogram the pcm, speed reads fine, no lights, etc. The Chrysler part # for the 3.90 is 5038703AG., I have a relationship w/ my dealer but purchased it for $730...... Just thought I'd throw this info out there!!
 

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I'm really new to Dodge/MOPAR stuff. Can you expand a bit on what you bought, what was needed to swap and how involved the install was? Thanks from a newbie.
 

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Discussion Starter #3
Yeah, no problem. The part # above is for a complete bolt in rear end/differential. The car uses CV axles so the install is extremely easy. Remove the exhaust for some room, then there are 4 bolts securing the diff to the chassis. There are 8-10 bolts holding the driveshaft to the diff. To the right of the shifter there is a small pocket that has a rubber pad that says “dodge brothers” this can be removed and under there is a latch with a red fabric loop. If you pull up on that then the driveshaft can be rotated to help with the bolt removal. Once the driveshaft is out of the way, and the differential is propped with a jack, you can slide the whole assembly forward a few inches to aid in removal of the back 2 bolts. Then you can slowly drop the diff down until you can pop out the cv shafts. No suspension removal is necessary. Installation is the reverse. Nothing else needed to be swapped. Again I have a 2015 Charger R/T with Road and Track package.
 

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Good info! Is that the rear end from the Mopar 11's?
 

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This is great news.

I am not trying t be a sharp shooter here but I am confused about your speed-o adjusting with the gear change. I take it you compared it to a GPS? Subtle tire size changes can effect it as much as 2mph. To tell the truth I do not fully understand how else the car gets its mph speed to read out.

I use HPTuners (as a novice on Dodge) and there are necessary parameters to adjust for a gear ratio change that would effect transmission shifting and characteristics. This and tire diameter changes (similar to a gear ratio change) need to be compensated for when changes are made.

Now as to the severity of the end-results if you do not re-calibrate for gear ratio is unknown to me on these vehicles (I'm mostly familiar with GM) but I have had to calibrate for trucks and you know how much the difference can be with these truck guys when it comes to gears and tires. When they put bigger tires on they shift too soon lugging into the next gear and will not kick down when they want it to.

Anyways I have posted up to the Dodge tuners about making gear changes without PCM/TCM calibrations and will get back to you be cause I want to know myself.
I run 2.65 gears and can only imagine the fun 3.90's would be and want to know myself how this effects calibration. I had no idea it would be this easy. Heck I would enjoy just doing it back and forth for when I do road trips.

I'll be back.
 

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The speed sensor is on the front wheels, not reading off the rearend like the older ones used too. Changing rear differentials has no impact on the speed. That makes this swap very easy and pain free.
 

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I did some calculations and a 5 speed NAG1 automatic with a 3.59 1st gear and a 3.90 rear ratio would be equivalent in first gear to a classic Mopar muscle car with a 4 speed and a 5.28 rear end ratio. You will get no traction in first gear and it will shift into 2nd pretty quickly. Drag radials will be a must!
 

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I just bought a 3.70 rear end and will be installing it as soon as it arrives. I'm kind of excited, going from the lame 2.62 open to 3.70 limited slip should be fun.
 

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I did some calculations and a 5 speed NAG1 automatic with a 3.59 1st gear and a 3.90 rear ratio would be equivalent in first gear to a classic Mopar muscle car with a 4 speed and a 5.28 rear end ratio. You will get no traction in first gear and it will shift into 2nd pretty quickly. Drag radials will be a must!
The NAG1 with a 3.90 rear axle ratio gives you an overall first gear ratio of 14.00:1. That is less torque multiplication than the 8 speed with the Scat Pack/SRT standard 3.09, which has a 14.55:1 overall first gear ratio. So the 3.90 swap seems reasonable to me for the NAG1. Had I driven a Scat Pack or SRT with a 3.09 while I still owned my 2012 R/T, I would have done the 3.90 swap myself. But my 2012 was totaled and I wound up getting a Scat Pack!

Too bad Dodge doesn't offer the 3.09 with the 5.7L/8 speed that would have been a nice combination.

RamAirV1
 

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Discussion Starter #17
I have decided to go get the pcm calibrated to the correct ratio. I still have no lights, etc. There have been a couple occurrences of the car bouncing off the rev limiter before shifting and super hard/awkward/ill timed downshifts.
I’ll update once I see how the calibration goes.
I would do the swap again in a heartbeat, having your 11 yr old screaming “too much!!!” as you are tail wagging into 4th from a standing start is priceless.
 

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I have decided to go get the pcm calibrated to the correct ratio. I still have no lights, etc. There have been a couple occurrences of the car bouncing off the rev limiter before shifting and super hard/awkward/ill timed downshifts. I’ll update once I see how the calibration goes.
I was going to be kind of shocked if you didn't have to do something. It would be nice though.

Just making shift point changes is kind of a pain in the A because of several table cells in the PCM and TCM pages requiring attention. There are a few threads on the HPT board with folks having trouble getting it right.
I managed to get mine moved up to 5800 RPM.

Please post back. I would like to take my 2.65:1 up a notch.
 

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You can get the 3.07 with the super track pack option in the R/T Road and Track or R/T Plus but the STP option is not available with the R/T Max.
Initially, on the 2015 they did offer the 3.09 on the Road and Track package for the R/T, but at some point the 3.09 option disappeared. It is not even available on the Daytona 5.7 now.

RamAirV1
 
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