4.10 to 3.73, worth it? - I've been reading a few other posts about swapping the ring and pinion gears to get a different ratio but I just want some ...

I've been reading a few other posts about swapping the ring and pinion gears to get a different ratio but I just want some more feedback. I have the 4.10 ration and I want to switch to a 3.73. I have the 1500HD truck and I want to maintain some of it's towing ability but I don't tow all that much so I was hoping to get better gas mileage by swapping the gears. It's 4WD so I would need to change the front and rear and it's a bit more expensive than I thought (~$500 for both sets, not including shims, bearings, gaskets, etc.)

My question is: will I really see a noticeable difference in gas mileage by going from a 4.10 to a 3.73 ratio?

I think not, but I just want to see what everyone else thinks. If it were $200-$300 I think I would do it but at somewhere close to $800, I question if it would even pay for itself before I get rid of the truck. I imagine that it's the 6.0L that's killing my gas mileage, not the gears...

I would say not. Unless your like me and put between 25-30k a year on your truck. I had an 05 Avy with 4.10's that I traded in on my Silverado with 3.08's. Both have 5.3's the Avy had a 4 speed and the Silvy has the 6. Going back and forth to work I've only seen about a 2 mpg increase with the Silvy.

If the ratio is raised (lower number) the truck may loose power, especially on hills and thus you might not gain any mileage. When changing gears on a 4x4 the front and rear must be the same ratio when operating in 4x4 or you will damage the transfer case or other drive line components.

Also, I am not sure you can fit 3.73 gears in the 4.10 housing, so you would need to change out the complete axle assembly.


Changing to oversize tires will lower the ratio.

I had an Avalanche with the 5.3 and 4.10 gears. My new Sierra had the 5.3, with 3.42 gears. Unfortunately, it's not a direct comparison, because the Sierra has a 6 speed tranny, and the Avalenche did not.
Anyway, the Sierra does get better mileage, but it may be the tranny. My guess is the fuel savings would not offset the cost of the change. If you do it, don't just go to 3.73. Go to 3.42 or 3.08 so you get more benefit. The engine will tow fine either way.

You may see about .5 MPG difference between the 4.10 and 3.73 maximum. Again, being a 4WD you would need to change both front & rear axle gearsets to same ratio. Housings are the same for 4.10, 3.73, 3.42 and 3.08 ratio gearsets. The drive pinion head is larger in diameter as the gear ratio decreases, gets smaller, but the machining of the ring gear compensates for it by being machined to different "thicknesses" for the various ratios. Example, a 4.10 would have a small diameter drive pinion head and a "thick" ring gear, where a 3.42 ratio would have a larger diameter drive pinion head, and a "thinner" ring gear. Same structural strength, just machined this way to keep differential cases common for manufacturing. All of the ratios EXCEPT the 3.08 have 41 teeth on the ring gear, and they vary the number of teeth on the drive pinion head to determine ratio. Example, 4.10 has 10 tooth drive pinion, 41 tooth ring gear. 3.73 has 11 tooth drive pinion, and 41 tooth ring gear, and 3.42 has 12 tooth drive pinion and 41 tooth ring gear. The 3.08 has a 13 tooth drive pinion, and 40 teeth on the ring gear. Not worth the costs, time or effort to go from 4.10 to 3.73 in my opinion.

Hey, thanks for the feedback guys. That was my hunch that it wouldn't make much of a difference. I was debating over installing a 3.42 ratio but then that would give me, what, a 1 mpg increase? I was crunching some numbers earlier and figured out that even with a 2mpg increase, it would take me 2-3 years to break even so if I'm only going to get a 0.5mpg increase, that would make it take like 8 years... I like wrenching on motor vehicles, and I've never done a gear swap before, so I thought it would be fun to do one weekend, but it seems like that's all it would be is fun!

From what I understand, the 1500HD had the option for the 4.10 or 3.73 ratios from the factory, thus my desire for the 3.73 gears. I guess it's wishful thinking to get "good gas mileage" from a 6.0L. I knew what I was getting into when I bought this truck to be a daily driver, but I was hoping for a little better than 12mpg average without towing anything. Oh well, I still love the truck, I'm an American, what can I say!

Do not change the ratio. Leave it as is.

I won't be changing the gear ratio. I figure that money could be put to good use elsewhere. Like nerf bars or new wheels... Or better yet, a down payment on a new two wheeled machine

feel good you get 12mpg My 6.0 L at best get 10mpg

The only time you should change out the gears is if you've put bigger tires on. The bigger tires will rob you of power and gas mileage. It's all about the math. If you go on google they make calculators so you can figure out where you want to be (power/mileage).