Switching from 3.92 to 3.21...

Gatornation9999

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How realistic / costly is it to switch a truck that comes with the 3.92 gear ratio back to a 3.21?

I’ve found several trucks that I like that have the 3.92 instead of 3.21, but I do not need the 3.92 as I do not do a lot of towing.

I realize this may be a really stupid question.
 

Accountant

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I think the problem would be FCA not allowing the sales code to be changed for warranty purposes. Not sure though.
 

Ramjack

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I think the problem would be FCA not allowing the sales code to be changed for warranty purposes. Not sure though.
What does this mean? Why is changing a sales code necessary? Is this what would change the necessary calibrations for the speedo and odometer?
 

Accountant

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Each VIN has a catalog of sales codes which are three digit codes for each accessory in the vehicle. So a tech would need to add this to the VIN using witech which also adds necessary programming for the accessory to function. Some codes are blocked by FCA.
 

Longhorn

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I'm not sure why you would need to change. The differences in fuel economy are negligible .

That answered my question, I was thinking it was because of the mpg’s so that has me thinking. Is the 5.7 best with the 3.92?
 

Billet1500 4x4

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That answered my question, I was thinking it was because of the mpg’s so that has me thinking. Is the 5.7 best with the 3.92?
depends on your driving split. City versus highway. Majority city the 3.92. Majority highway the 3.21. Even split probably about the same maybe 3.92 would do better. The trucks uses the most fuel to accelerate once up to speed not so much so 3.92 will make it easier to get up to speed. 3.92 would be much better if you plan on putting on bigger tires as well. The 275 55 20 on these trucks look small even when they're stock height.
 

Gatornation9999

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I do mostly highway (some city). And only tow a family boat 2-3 times a year. From what I’ve read on here, the differences in highway MPG look to be anywhere from 3-5 MPG, which I do not find negligible. Oh well, probably just named to keep looking or order so that I can get what’s best for my situation.
 

Ramjack

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I don't consider 2mpg to be negligible when the baseline is 15-22 mpg.
 

202snowman

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I don't consider 2mpg to be negligible when the baseline is 15-22 mpg.
It's about $450 a year, assuming 18,000 miles, $3 gas, and 16 versus 18 mpg.

Take that against the cost of changing out 3.92s to 3.21s like the original posted asked and Im guessing you don't get payback for at least 3-4 years...i thought I had read in other forums that it would take a couple thousand dollars to change out the gearing (I might be mistaken)
 

RT70808

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It's about $450 a year, assuming 18,000 miles, $3 gas, and 16 versus 18 mpg.

Take that against the cost of changing out 3.92s to 3.21s like the original posted asked and Im guessing you don't get payback for at least 3-4 years...i thought I had read in other forums that it would take a couple thousand dollars to change out the gearing (I might be mistaken)
3.21’s on my fat heavy limited don’t really make much of a difference when I’m only getting 13-16
 

troutspinner

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You don’t see people swapping from 3.92 to 3.21 but you do see ALOT of people asking to swap the other way around.

This is going to sound harsh but I mean it in the lightest sense. If you’re worried about gas mileage on a 50k+ truck. Maybe you shouldn’t be buying a truck or at least buy a cheaper one or a car that gets great gas mileage.
 

mikemcfarland

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You don’t see people swapping from 3.92 to 3.21 but you do see ALOT of people asking to swap the other way around.

This is going to sound harsh but I mean it in the lightest sense. If you’re worried about gas mileage on a 50k+ truck. Maybe you shouldn’t be buying a truck or at least buy a cheaper one or a car that gets great gas mileage.

toyota prius with a u-haul ?:p
 
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mikemcfarland

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You don’t see people swapping from 3.92 to 3.21 but you do see ALOT of people asking to swap the other way around.

This is going to sound harsh but I mean it in the lightest sense. If you’re worried about gas mileage on a 50k+ truck. Maybe you shouldn’t be buying a truck or at least buy a cheaper one or a car that gets great gas mileage.
hey @troutspinner - you are doing some GREAT things to you ram and a great contributor. can you do a signature and let us all know?
 

Couchsachraga

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I was originally planning on 3.21 myself for the (admittedly marginal) higher mileage, but wanted the extra tow capacity. Salesman said he personally only orders 3.92 (or similar) ratio for himself now as it is "more fun" and the MPG difference was 1-2mpg (which I pointed out was around 10%...). My driving is very mixed - winter time commute is short with some stop and go (eTorque will hopefully help there), but any longer trips tend to have very little stopping (rural area) and "modest" speed (50-60mph... not interstate). I'm assuming it will be similar to my current SUV... we'll see, but either way I'll agree with folks that if you are looking for great mileage you can't look at any of the full size trucks (though the I6 3L diesel in the GMC / Chevy next year looks interesting...)
 

lowell3170

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My 2013 Ram 1500 V6 can pull a 18 foot boat with ease and 3.21 rears. I bought it new in 13 and have 55000 miles on it . My MPG in warm weather id 22.5 to 25.5 and have gotton 27.7 on a full tank run. That little motor will shock you when passing other vehicles. I did order a 2019 Laramie with the V6 in August and waiting for it to arrive. Those 3.92's will kill your MPG. for sure.
 

Ramjack

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It's about $450 a year, assuming 18,000 miles, $3 gas, and 16 versus 18 mpg.

Take that against the cost of changing out 3.92s to 3.21s like the original posted asked and Im guessing you don't get payback for at least 3-4 years...i thought I had read in other forums that it would take a couple thousand dollars to change out the gearing (I might be mistaken)
Yeah, I agree with you that paying to swap out the rear end may not be worthwhile. I guess I was commenting that a 2mpg difference (if accurate) is more than negligible when considering which rear end you might want when initially buying the truck.
 

19RamLimited

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I have 3.21 and my mileage is not any good. Granted I drive it and am not shy with the gas pedal. I don’t think you’ll see any benefit for the cost and trouble. I don’t think you would see any difference.

Plus as someone mentioned above trying to get the truck corrected for the gear change. Trans strategy and engine calibration. The only real way would be to have the sales codes added. And then you need a dealer to download the config and possibly red lash the ecm and maybe trans.
 

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