Pros/Cons on gear swap/ GearVendors OD

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smketrfdny

smketrfdny

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One other thing that caused my old 2006 to lose fuel mileage was when I replaced the OEM Michelin tires to the newer Michelin LTX A/T2 and saw a lost of 1.5 mpg, also noticed I could keep air when empty at 60-65 front and 55-60 rear... IIRC my best mpg numbers was 55-57 MPH, as I recall the max TQ with the 3.73 was around 1500 rpm's once over 2050 rpm's MPG started to drop....
Yea, i was told years ago 2k rpm was tops for the better mpg. But im hitting 2k at 65, whereas the 02 F250 i was hitting at 70, im thinking 3.73. i topped 20 numerous times on trips with it (then again, was a 2dr not a 4dr, and obviously less weight). I may go with the 3.73 or 3.55s thinking that a post above made a good point that while the GV is a nice addition, its just another thing to possibly break down. Retiring in Dec, so ill get it done after i retire. Just need to find a good guy to do it.
 

Blue Truck

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My truck has the GV unit, but I'm running 3.73 gears and an NV5600. Drops my 70 MPH RPM from around 2,100 to around 1,700 IIRC. Since I almost never do a full tank of driving that's mostly higher speeds, I can't give you a full tank, scientific MPG comparison, but on tanks where I get to run OD for 1/3 to 1/2 of the tank I'm not noticing a difference in MPG. Yeah, not what I expected either. Aerodynamics are cruel. Realistically, it's probably giving me a slight improvement when it's engaged, but it gets lost in the big picture of my real world driving.

Another thing about the GV unit to consider is maintenance. Last night I was on my back in the gravel driveway to change the roughly 1-1/4 quarts ($25 + tax worth) of Lucas synthetic gear oil, something you should do every 5k miles. One more thing to maintain...

I had 4.10 gears in my 1st gen truck, and I hated them. Bet you'd like your truck a lot more if it had 3.73 gears. Unless you're towing heavy frequently and need the 4.10's, I think you'd be happy with a gear ratio swap and some slightly taller tires. Not sure what the going rate for a F/R axle gear swap and speedo correction is, but I bet it's a whole lot less than a GV install. Bet that the whole GV package with installation would run you $5k or so. Would I buy one if the truck didn't come with it? Nope. If mine ever croaks, will I replace it? Nope, I'll put a stock tail shaft and driveline back in.

YMMV...literally.
 
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smketrfdny

smketrfdny

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My truck has the GV unit, but I'm running 3.73 gears and an NV5600. Drops my 70 MPH RPM from around 2,100 to around 1,700 IIRC. Since I almost never do a full tank of driving that's mostly higher speeds, I can't give you a full tank, scientific MPG comparison, but on tanks where I get to run OD for 1/3 to 1/2 of the tank I'm not noticing a difference in MPG. Yeah, not what I expected either. Aerodynamics are cruel. Realistically, it's probably giving me a slight improvement when it's engaged, but it gets lost in the big picture of my real world driving.

Another thing about the GV unit to consider is maintenance. Last night I was on my back in the gravel driveway to change the roughly 1-1/4 quarts ($25 + tax worth) of Lucas synthetic gear oil, something you should do every 5k miles. One more thing to maintain...

I had 4.10 gears in my 1st gen truck, and I hated them. Bet you'd like your truck a lot more if it had 3.73 gears. Unless you're towing heavy frequently and need the 4.10's, I think you'd be happy with a gear ratio swap and some slightly taller tires. Not sure what the going rate for a F/R axle gear swap and speedo correction is, but I bet it's a whole lot less than a GV install. Bet that the whole GV package with installation would run you $5k or so. Would I buy one if the truck didn't come with it? Nope. If mine ever croaks, will I replace it? Nope, I'll put a stock tail shaft and driveline back in.

YMMV...literally.
Even better info, thanks. I'll stick with the gear swap as originally planned. Yep, i wont get 30 mpg with a 7000 lb truck with the aerodynamics of a brick, but anything is better than now. Even if i drive nationwide a few months a year with a camper, i dont see me needing 4.10s. While someone posted my 5.9 may be overkill for towing, should i decide to go bigger, the Cummins will be better if i go bigger (doubt ill go with a 5th wheel). With that being said, i may get a side gig after retiring and maty do a ton of driving with things to sell/demo. So im sure the $$ spent on a gear swap may be worth it. Thanks again.
 

rosco11

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Good Afternoon. As i thought, I get better answers here than the usual social media. Anyway, I have the 07 MC 5.9 Cummins SRW with 4.10s. Would prefer better mpg with fuel costs, as I'm sure many would as well. With that being said, upon retirement I am looking into the RV scene. Nothing big like a 5th wheel (would prefer a dually for the 5th), and its just me for now, so prefer a smaller trailer. I do realize I can pull a house with the 4.10s, but also prefer better mpg. And yes, Im aware pulling anything no matter what the gear will lower the mpg.

With that being said, taller axles (3.55, maybe????) may make a difference when not pulling. While i may do a decent amount of traveling towing a camper, I still do a lot of driving without one (not buying the camper till after retirement in December), hence the post. The other option is the GV OD. Not towing, GV will lower the 4.10s to 3.20, which isnt bad, correct? Talking to GV, you cannot tow when using it, so it seems that keeping the 4.10s and adding the GV seems to be the best bet. FWIW, I may have 'answered my own question' and maybe so, but any opinion from those with extensive knowledge with either or would be appreciated. Many thanks in advance, safe travels.
First, to make any noticable difference, you would have to go from 4.10 to something like 3.06. And you are only going to get 2 or 3mpg gain, the trade off being more wear and tear on your engine and transmission. Swapping to 3.73 or 3.50 is not going to get you anything noticable. it will take a hundred thousand miles just to break even for the cost of the gears and labor.

The problem is not your gears. The problem is you expect a 6 to 7000 lb tow beast to give you some efficiency in the fuel tank. The tool you want is at odds with your expectations. Sell it and buy a 1500 and a small travel trailer. That is how you get better millage. Gears will not help you.
 
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smketrfdny

smketrfdny

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First, to make any noticable difference, you would have to go from 4.10 to something like 3.06. And you are only going to get 2 or 3mpg gain, the trade off being more wear and tear on your engine and transmission. Swapping to 3.73 or 3.50 is not going to get you anything noticable. it will take a hundred thousand miles just to break even for the cost of the gears and labor.

The problem is not your gears. The problem is you expect a 6 to 7000 lb tow beast to give you some efficiency in the fuel tank. The tool you want is at odds with your expectations. Sell it and buy a 1500 and a small travel trailer. That is how you get better millage. Gears will not help you.
I'll respectfully disagree. I dont think asking for 20 mpg is a problem. Scroll back and see where i dont expect to get 30 mpg. And where another post the gentleman got 20 with 4.10s and a dually. So i dont see it as a problem with a 7000 lb truck with the aerodynamics of a brick. Ive thought about dropping a 6MT as well and leaving the gears. Would those 2 extra gears make a difference? I'm sure the answer can be posted by you or someone else. Like I posted, if i can improve the mileage, 100k more miles wont be an issue so the break even point wouldnt be that long. And while 150K miles is minor league for you and others, I think its good for another 350K or more. And no issues driving it cross country once retired, it actually rides nice. But for pulling anything, would the 3.06 be too tall? Thanks.
 

06 Dodge

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I'll respectfully disagree. I dont think asking for 20 mpg is a problem. Scroll back and see where i dont expect to get 30 mpg. And where another post the gentleman got 20 with 4.10s and a dually. So i dont see it as a problem with a 7000 lb truck with the aerodynamics of a brick. Ive thought about dropping a 6MT as well and leaving the gears. Would those 2 extra gears make a difference? I'm sure the answer can be posted by you or someone else. Like I posted, if i can improve the mileage, 100k more miles wont be an issue so the break even point wouldnt be that long. And while 150K miles is minor league for you and others, I think its good for another 350K or more. And no issues driving it cross country once retired, it actually rides nice. But for pulling anything, would the 3.06 be too tall? Thanks.
IMO yes 3.06 gears are way to tall, heck Ram stopped using the 3.42 and went back to 3.73 for a reason, with all things being equal to my 06 5.9 CTD SB Auto 4x4 either you got one of those engines that will only get set mpg no mater what, your tires are eating 1-2 mpg, speeding or its your right foot....
 
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smketrfdny

smketrfdny

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IMO yes 3.06 gears are way to tall, heck Ram stopped using the 3.42 and went back to 3.73 for a reason, with all things being equal to my 06 5.9 CTD SB Auto 4x4 either you got one of those engines that will only get set mpg no mater what, your tires are eating 1-2 mpg, speeding or its your right foot....
May have to go with your engine point. I dont have a lead foot. i keep it under 2k rpm most of the time. Tho i will write off the 1-2 you mentioned due to living in a hilly area, the mpg is still about the same than when i lived on mostly flat long island. I had 3.73s in my 02 F250, and loved it, but had a family for a short time and traded it in for the MC. As posted, even with any change, big or small mpg wise, I'll take the gear change for the traveling. Did most of my camping at Camp Marriott, and Im going intro the RV scene with no experience and very little knowledge. Should i like it, one good reason to keep the diesel should i go bigger. Thanks again
 
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06 Dodge

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May have to go with your engine point. I dont have a lead foot. i keep it under 2k rpm most of the time. Tho i will write off the 1-2 you mentioned due to living in a hilly area, the mpg is still about the same than when i lived on mostly flat long island. I had 3.73s in my 02 F250, and loved it, but had a family for a short time and traded it in for the MC. As posted, even with any change, big or small mpg wise, I'll take the gear change for the traveling. Did most of my camping at Camp Marriott, and Im going intro the RV scene with no experience and very little knowledge. Should i like it, one good reason to keep the diesel should i go bigger. Thanks again
My self I would try bigger tires before going to a gear change... I would check the tire route of going from stock 265/70/17 to 285 or 295/70/17, my OEM Michelin tires had A/S tread similar to this tire in load rage E: https://www.tirerack.com/tires/tire...7DLTXOWL&vehicleSearch=false&fromCompare1=yes

FYI I lost almost 2 mpg mpg city driving when I replaced the stock all season Michelin tires for the Michelin LTX A/T 2 tires....
 

olddog

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My truck has the GV unit, but I'm running 3.73 gears and an NV5600. Drops my 70 MPH RPM from around 2,100 to around 1,700 IIRC. Since I almost never do a full tank of driving that's mostly higher speeds, I can't give you a full tank, scientific MPG comparison, but on tanks where I get to run OD for 1/3 to 1/2 of the tank I'm not noticing a difference in MPG. Yeah, not what I expected either. Aerodynamics are cruel. Realistically, it's probably giving me a slight improvement when it's engaged, but it gets lost in the big picture of my real world driving.

Another thing about the GV unit to consider is maintenance. Last night I was on my back in the gravel driveway to change the roughly 1-1/4 quarts ($25 + tax worth) of Lucas synthetic gear oil, something you should do every 5k miles. One more thing to maintain...

I had 4.10 gears in my 1st gen truck, and I hated them. Bet you'd like your truck a lot more if it had 3.73 gears. Unless you're towing heavy frequently and need the 4.10's, I think you'd be happy with a gear ratio swap and some slightly taller tires. Not sure what the going rate for a F/R axle gear swap and speedo correction is, but I bet it's a whole lot less than a GV install. Bet that the whole GV package with installation would run you $5k or so. Would I buy one if the truck didn't come with it? Nope. If mine ever croaks, will I replace it? Nope, I'll put a stock tail shaft and driveline back in.

YMMV...literally.
I agree with this, it mirrors my experience with Gear Vendors. The GV will not tolerate negative torque such as an exhaust brake. When towing heavy, an exhaust brake is likely to be more important to many users. My Gear Vendors broke into chunks internally from normal towing with the stock Cummins and no exhaust brake at about 60,000 miles. I also removed the unit and had a new driveshaft made to restore the driveline to stock. The Gear Vendors had minimal improvement to mileage. My 2003 has a 3.73 gear with the auto tranny, and I think it's close to perfect for a final drive ratio. I would not recommend the Gear Vendors to anyone for towing, or reliability behind a torque motor like the Cummins.
 
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