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Discussion Starter · #1 ·
Hello all,

I have a 2012 Ram 1500 ST 4X4 Quad cab with the 4.7L engine in it.

In the rear end I have 3.55 gears with an open differential.


I have a camper that is just bumper pull, fairly small. I'd say we're talking about 4000 pounds, maybe 4500 when its loaded.


Here's the issue I'm running into. Even driving on flat highway, I can't tow in anything above 4th gear. Now, when we start going up a hill 3rd is required for a smaller hill, and if its a big hill, or a long hill, typically 2nd is required to keep up 60-65 mph.


I have looked into trading in for a different pick up, but I have low miles (67000) that it will take a lot of extra money to trade into anything similar to mine with a bigger engine (say the Hemi, or the bigger Chevy). By my calc's and looking around at whats for sale, its safe to say it would cost me at least $4-6k for any upgrade in vehicle and more likely will end up with high millage as well.


That's when I had a bright idea, why not improve my current truck to make pulling better.

Plan: swap out the gears from 3.55 to 4.56 for both the front and rear. Part will run about $500 give or take. Installation is unknown, and I still need to research who would be best at changing them out in the Sioux Falls Area.


While I'm at it, I hate my open differential. I honestly can't fathom why its even an option from the factory, but that's another battle... I found I can get a Detroit trutrac limited slip differential for roughly $500-600. Installation is again a big unknown.



I'd like some input with what I am proposing. I understand that fuel millage may get worse, but I tell you what right now I am lucky to get 14 MPG on the highway, and lucky to get 8 MPG while towing my trailer. I have a feeling the better gear ratio honestly might even help with millage...


Also I just picked Detroit Trutrac, if there is a better option please advise.
 

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DTT is fine. Your around town mileage may improve because the engine isn't working as hard to get the truck moving but keep in mind it's a huge jump from 3.55 to 4.56. Hands down your highway mileage is going to fall badly. You will find it easier to tow with the better mechanical leverage.
 

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Swap

Swapping over from a 3.552 a 3.92 it’s like changing your brakes. Everything should lineup Exact. Considering you have a 4 x 2 I just did it last week and it took about three hours to do the complete job that was also changing pads and rotors. I purchased a used 3.924 $600, the stickers were missing, I feel absolutely no difference. I have a feeling I just swapped out at 3.55 for another 3.55. But the overall swap, pretty easy.
 

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Sell the truck and get the one you need. A lot less head ache than changing both front and rear diff parts. Cost will probably be more than you expect and if you insist on doing it I would get a complete front and rear diffs from an auto wrecker, that way you don't have to worry about if the gears were properly set up for lash.
 

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Swapping over from a 3.552 a 3.92 it’s like changing your brakes. Everything should lineup Exact. Considering you have a 4 x 2 I just did it last week and it took about three hours to do the complete job that was also changing pads and rotors.
No he has a 4x4

Sell the truck and get the one you need. A lot less head ache than changing both front and rear diff parts. Cost will probably be more than you expect and if you insist on doing it I would get a complete front and rear diffs from an auto wrecker, that way you don't have to worry about if the gears were properly set up for lash.
Definitely not the cheaper route. Worst case scenario a couple grand in parts and labor.
 

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Sell the truck and get the one you need. A lot less head ache than changing both front and rear diff parts. Cost will probably be more than you expect and if you insist on doing it I would get a complete front and rear diffs from an auto wrecker, that way you don't have to worry about if the gears were properly set up for lash.

This, at the end of the day you'll still have a 4.7. Honestly it sounds like your truck is doing just fine, its towing, just not going into overdrive, which is really probably better for your transmission
 

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Discussion Starter · #7 ·
Well, I looked around and test drove a couple trucks.

At the end of the day I test drove a 2015 eco diesel. I tell you what, it pulled that camper super easy, real pleasant to tow. But at the end of the day, it will cost over $8k to make that upgrade. Most disappointing thing about the eco diesel was not all that efficient.

Towing with my 4.7 I get 8-9mpg, while the diesel got 12 mpg. Now I can buy a lot of gas before that diesel pays off. Same with high way 15/16 mpg vs. 21.


Still contemplating the gear swap, going to go get some quotes to see what it would cost. At the very least I want to swap to a limited slip differential. I spend far too much time off road or on minimum maintenance roads to have an open differential.
 

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I have contemplated gear swaps numerous times over the years and the estimates always fall in the range of $1000 per axle. I've never pulled the trigger yet but have usually ended up with what I wanted by eventually changing vehicles.

I wished my 94 and 95 V10's had 373's instead of 355's, I wished my 03 Cummins dually had 355's instead of 373's. I wished my 02 1500 had 392's instead of 355's and my 03 had 355's instead of 392. See the trend here?

I put just over 225k miles on my 02 Ram QC 2wd with a 4.7 and 3.55's but only did light towing, (tandem jetski trailer plus a 12ft enclosed trailer). Average mileage was 17.8 on my daily commute which ranged from 60-65mph. Mileage dropped to 12-14 while towing on the Interstate at 75-79 MPH. I looked into 392's but the truck never really gave me a real reason to spend the money.

My next 4.7 was an 03 Laramie QC 2wd that came with the 3.92's, (left gears but did swap the OEM LSD for an Auburn LSD), and while it towed better, the mileage was down in the 14mpg range and it was not a great truck to travel the Interstates in. I actually contemplated gearing back up to the 355's but I didn't like the truck enough to invest any more money in it than necessary to keep it on the road.

I never warmed up to the truck so I traded it off on a 2017 Ram Limited with the 5.7 Hemi, 8 spd auto and 392's and I couldn't be happier. I would normally say the 392's are too low a ratio if you plan to do any amount of highway driving but the 8spd transmission makes a huge difference and keeps the rpm in a reasonable range.

Based off my personal experience, I'd stick with what you have until you are ready for a real upgrade.
 

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It cost me $1200 but i did a complete rebuild of my factory axle in addition to swapping the OEM LSD for an Auburn unit. If I had wanted to do gears at the same time, it would have only cost me the amount of the actual gears which would have been around $150, IIRC.

Had I known I was going to be changing jobs and doing way more highway driving, I would have swapped to 355's.
 

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Discussion Starter · #11 ·
Good info. I think I've been convinced to keep my current set up, but I'm going to work on getting a new differential so I can play in the snow and not have to shovel so much!
 

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The Ecodiesel will blow away the highway mileage on the 4.7, both empty and towing. You said yourself how easily it pulled your TT. I have had 33 mpg hand calculated on my 15 4x4 CC ED with a 6'4" box Your 4.7 will never touch that and the ED has more available and torque than even the Hemi. If the ED has the Anti-spin rear it will give you all you need to do what you are looking at and is a lot newer than your current vehicle. My ED gets me 16-18 pulling my 6k TT.
 

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Discussion Starter · #13 ·
The Ecodiesel will blow away the highway mileage on the 4.7, both empty and towing. You said yourself how easily it pulled your TT. I have had 33 mpg hand calculated on my 15 4x4 CC ED with a 6'4" box Your 4.7 will never touch that and the ED has more available and torque than even the Hemi. If the ED has the Anti-spin rear it will give you all you need to do what you are looking at and is a lot newer than your current vehicle. My ED gets me 16-18 pulling my 6k TT.

The Eco I drove didn't get anywhere near what you're saying.. I was honestly really disappointing because I wanted it to be as good as what you're saying. I did the math, and because diesel is more expensive than regular, the ecodiesel was barely cheaper per mile. At today's fuel prices ($2.75 gas, $3 diesel) the one I drove came out to be $0.136/mile highway (60mph) and $0.25/mile towing (60mph). My 4.7L can do $0.171 highway (75MPH) and $0.30/mile towing (60mph).

Looking at those values, I can't justify the price of the ecodiesel. It was a massive let down to be honest. Made I got a bad truck, but I was really let down from almost all points of view...
 

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I got a bad Cummins so it does happen. No fault of the manufacturer, it was an ex oil field service truck, buyer-beware kinda deal. It made great power but the low mileage and extensive repairs quickly undermined any justification I used to convert from V10's to the Cummins.

IMO, diesel for a daily driver/occasional tower hasn't made economical sense since the late 90's when diesel passed the price of gas and they started trading torque for HP.

There used to be a big gap between the gassers and diesels as far as pulling power with the only options being big blocks getting under 10 mpg. The newer V8's have closed that gap with more pulling power than ever while getting mileage that was unimaginable just a few short years ago so if your not maxing out your payload on a regular basis, the justification just isn't there. Not financially anyways.

I hate the smell and clack-clack sound of the diesels too, so for me, it's an uphill sell right from the get go. I do love the torque they can put down but I'm past the stage in life where my testicles make my decisions. :)
 

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I saw a truck stop last weekend with diesel for $2.99/ gallon which I thought was pretty good, but that was the cash only price and gas is still cheaper. I'm not aware of many, if any, areas in the US with diesel that costs less than gas
 
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