I know you can't give me a definate answer to this question, but all things being equal, what kind of mileage should I see with my new 3.54 gears over the 4.10 gears I had? I was getting just under 18 MPG towing a car hauller trailer on the highway. I never checked empty but I'm guessing I was doing a mile or two better.

BTW, I think this electrician now knows more than most of the guys that work in the gear and driveline shops in a 200 mile radius of me. Things I've learned that several people told me would or wouldn't work that were not true. 1) the carrier and gears from the front of a '89 W250 will NOT work in the rear of a Ford F250 D60. 2) The 3.54 gears from the front of a '89 W250 WILL work with the Ford carrier in the rear of a F250 D60.

 

I would think pulling you mpg will go down with the 354 the 4-10's are the pulling gear of choice I know with my crewcab I had 4-10's and big tires and it averaged 18 or better empty pulling i got around 16 but even that was awesome compared to a 440 gasser that was gettin 6 and the only thing it could not pass was a gas station .

 

youll loose some of the low end grunt but once your are up to speed your RPMS will be considerably lower meaning you can tow a little faster and you should get better mileage. What size tire? I have 410s with the stock sized wheels on my truck and towing over 65MPH the revs are just to high and it starts to suck down the fuel. It if had 373s or 354s it would drop it down to under 2k and be more efficient. keep us updated thinking about the swap myself.

 

i have 3:54's and it runs about 2k rpm to run at 65 with slighly shorter than 235 85 r16's loaded i get 15mpgs buts thats about 12k behind me

 

I love my 4:10's and the low end for towing is sweet. At 60 mph the tach is at 2100.

 

I finally have the time to update this. I changed the gears out mid July. I went from my best of 17 MPG with 4.10's to 23 MPG with 3.54's running 70 on the interstate. I went down to 20 MPG @ 75. The truck is way quieter at highway speeds, now I need to do something about the wind noise.

 

The tried and true method to stopping wind noise is to install a louder exhaust

 

Turning up the radio works for me.

 

12 GVW RV with RH47 AT and OD and 456:1 Dana 70 turning 8R 17.5 tires.
I think I'm turning 2300 at 60. Does 411:1 seem like the right numbers asI am definitely going to change something?