[2ndAmend]

Ok, just took the plunge and ordered the 3.90. Found a website selling it for $703, and they are less than an hour drive so I can avoid shipping and do local pick up. (No sales tax here.) So, it seems like short money and going to give it a try.

Seems like a pretty straight forward install so I'm thinking about doing it myself. I don't have a regular lift but I have the Quick Jack and the SUV spacers so the lift will give me about 24+", plus the rubber bumpers on the rear lift points add another 1" or so about 25-26" total floor to frame.

Dealer wants about $300 to do it. I do almost all my car maintenance but I don't do engines, trans, and never did a diff. I don't have a real job so I have plenty of time.

I'd like to hear from you guys that did the swap to let me know the difficulty of the job and any suggestions/info/warnings you can share.

Thanks!

 

[Frosty]

With no lift and only $300 to have professionally installed I personally would go that route and I'm like you with not wanting others working on my car. I'd say to bring it over and we could throw it on my lift but that might be a bit of a drive for you ;-)

Tuned in as I'm curious how much of a difference you feel.

 

[2ndAmend]

1MileShooter said in my other thread:

In my 2015 M6 I installed (at the dealer) a 3:90 pumpkin from Mopar at about 15,000 miles (I bought brand new) and it made an immediate difference in all around performance--also much more manageable on hills and in Kalifornia stop and go traffic--the car is geared too high from the factory--the 3:90 gear is an absolute must performance upgrade and "drivability" upgrade--an extra benefit is extended clutch life--when I sold the car with 51,000 miles on it, the car still had the factory original clutch which performed flawlessly. There's NO downside, only improvement--also the car pulled much stronger on the top end as torque was maximized. This should be the #1 modification before all else.

JUST DO IT!

So I...

 

[Frosty]

If it's not to much trouble would you be willing to do a before and after of gear vs rpm at a couple speeds? Like 45mph, 60mph and 75mph (my local highway speed limit not sure what yours is though).

I'm curious on how much higher the car will be reving at cruise speeds. I assume only 100-200 more but real curious.

Also, mind sharing where you are getting it here or in PM? That seems like a good price even if I had to ship.

 

[ezlife45]

If it's not to much trouble would you be willing to do a before and after of gear vs rpm at a couple speeds? Like 45mph, 60mph and 75mph (my local highway speed limit not sure what yours is though).

I'm curious on how much higher the car will be reving at cruise speeds. I assume only 100-200 more but real curious.

Also, mind sharing where you are getting it here or in PM? That seems like a good price even if I had to ship.

Do the math, it's easy. Take your speed rpm numbers and multiply by 3.9/factory ratio.

 

[MXS67454]

delete

 

[Quasar Z]

I did mine with a Quickjack and it wasn’t a lot of fun. Two people would help immensely but I was alone at the time and just wanted to get it done. I ended up nicking one of the axle seals and got to basically do the job twice. I do all of my own work but for $300 I think I would let someone else handle this if I needed to do it again.

 

[snobrdrdan]

I do all of my own work but for $300 I think I would let someone else handle this if I needed to do it again.

x2 on this

I did it myself before and it wasn't too terrible, but wasn't much fun either with the car on ramps and me on the floor.
That said, $300 seems like a VERY fair/good price for someone else to do it

 

[Slidd]

If it's not to much trouble would you be willing to do a before and after of gear vs rpm at a couple speeds? Like 45mph, 60mph and 75mph (my local highway speed limit not sure what yours is though).

I'm curious on how much higher the car will be reving at cruise speeds. I assume only 100-200 more but real curious.

Assuming a loaded tire diameter of 28 inches it works out like this.

3.70
45 - 1259 rpm
60 - 1678 rpm
75 - 2097 rpm

3.90
45 - 1327 rpm
60 - 1769 rpm
75 - 2211 rpm

So not a lot of difference.



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[Varooom]

Would you please post where you got it and the part number?
Thank you,
Varooom

 

[OldMoparGuy]

Assuming a loaded tire diameter of 28 inches it works out like this.

3.70
45 - 1259 rpm
60 - 1678 rpm
75 - 2097 rpm

3.90
45 - 1327 rpm
60 - 1769 rpm
75 - 2211 rpm

So not a lot of difference.



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Hardly seems worth the expense and effort. Greater improvements although more expensive, are made with tranny gearing.

 

[motorheadmike]

Hardly seems worth the expense and effort. Greater improvements although more expensive, are made with tranny gearing.

The mechanical advantage is there without giving up much torque capacity in the driveline by using a TR6060 out of a Scat Pack or going full blown built TR6060 with better gears and internals.

 

[baabootoo]

If you have to ask................ Will you offer a warranty on the work?????? Let them do it and carry the burden.

 

[DSmith]

Found this diff at mymoparparts.com for $709 plus shipping:
68427798AA - FCA Differential. Rear axle | Libertyville IL
I'm curious, is there a better quality aftermarket option available?

 

[2ndAmend]

Would you please post where you got it and the part number?
Thank you,
Varooom

The P/N was on several other threads, I ordered the 68427798AA.

 

[2ndAmend]

If you have to ask................ Will you offer a warranty on the work?????? Let them do it and carry the burden.

Couple things: Serv Mgr said it would not affect the warranty on the rest of the car. Also, though the diff comes with the Mopar warranty, the diff may not be warrantied in a HC, but I trust this SM to stand behind their work (labor).

The downside is 1) $300 (estimated, maybe slightly more), and 2) the installation is in the permanent record. A self install can be reversed with no record of it ever have happened.

 

[2ndAmend]

Hardly seems worth the expense and effort. Greater improvements although more expensive, are made with tranny gearing.

You are absolutely correct, but the 3.90 is relatively cheap and easy, and easily reversed. 16GoManGoHC did the 1st gear change (plus a few other things) and he has a rocket!

 

[2ndAmend]

Looks like lots of dealers are running a web store out of their parts dept, search and maybe you will find one local to you. Here are some I looked at:

	Diff	Ship	Total	Confirm Fit
68427798AA	$690​	$85​	$775​	no	68427798AA - Rear Axle Differential - 2015-2021 Dodge Challenger | Mopar America 2015-2021 Dodge Challenger Rear Axle Differential 68427798AA www.moparamerica.com
68427798AA	$710​	$154​	$864​	yes	2021 Dodge Challenger Differential. Rear axle - 68427798AA | Myrtle Beach SC Differential. Rear axle. 2021 Dodge Challenger. Genuine Dodge Part - 68427798AA. Ships from Myrtle Beach SC www.moparpartsinc.com
68427798AA	$722​	$199​	$921​	yes	2020 Dodge Challenger Differential. Rear axle - 68427798AA | Factory Chrysler Parts, Bartow FL Differential. Rear axle. 2020 Dodge Challenger. Genuine Dodge Part - 68427798AA. Ships from Factory Chrysler Parts, Bartow FL www.factorychryslerparts.com
As of 5/6/21:
68427798AA	$960​	$75​	$1,035​	no	More Information for MOPAR 68427798AA
Rochester, NH
	$703​	$90​	$793​	no	2015-2021 Dodge Challenger Rear Axle Differential 68427798AA | Mopar Discounts 2015-2021 Dodge Challenger Rear Axle Differential 68427798AA www.mopardiscounts.com
	$703​	$77​	$780​		15% Off Shipping on Orders $300+ | GET15

 

[Slidd]

And whatever price Steve White Parts is showing use discount code CHA1 for a little more off.


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[Rcolonfdny]

Im the new guy. Just trying to read and educate myself. Can someone tell me what a 3.90 final drive does? What do our cars come with now? Why would i want this? How does it hurt or help the car?
Thanks