I had to special order a 2013 F-350 extended cab SRW 4X4 Diesel.I made a big mistake with the axel ratio and just took what came with the truck. It seems like I made a big mistake because the truck came with a 3.31 non-limited slip that is too high with the 6 speed transmission. I feel I should have ordered 3.73 if I had know.
Why do I make the above statement?
I traded in a 2006 F-350 extended cab SRW 4X4 Diesel that had 87000 miles with no problems till 47000 miles then started to blow turbochargers. That truck came with a 7.73 limited slip axle from a dealer lot. The 06 truck got 15.5 MPG non-towing and 10/11 towing. The 2013 truck gets 13.5 MPG non-towing and 9/10 towing. I am towing the same 5^th wheel trailer with both trucks and the same route from Oregon to Texas. The other day I was towing my 1988 Suzuki Samurai on all four weighting 2300 lbs.. I only had to go 30 miles but as a experiment I locked the transmission into 5^th gear and got 15.5 MPG (6^th gear 13.5 non-towing).

I want to change the gears but in reviewing the Ford build and price website for some reason the only way to get the 3.73 limited slip is electronic and DRW only. There are a mess of mistakes on their website (no rear sway bar) and the salesman did not pick up the no sway bar and I feel the too high axel gear. Just two miles per gallon can save over $3000 at 80,000 miles. That’s the cost of the gear change.

What are your thoughts? Don’t tell me I’m nuts, I already know that. It still will not change my mind because I’m a retired old fart who wants better MPG over 80,000 to 100,000 miles that I hope to put on this truck unless someone can give me a VERY GOOD reason why I should not do it.

I really would appreciate any suggestions for or against the gear change or even a better way to do it.

 

3.31's and 3.55's are your only option for the SRW diesel. You can change them, just gotta fork out the $$$ for it, which I don't think would be worth it.

Your empty mpg's concerns me a little, you should be doing better based on what I've read in the 6.7 forum. How many miles on the truck?

 

That pretty much sucks. Did you build it out yourself or did the dealer help? A person experienced in building trucks should have known better. That being said, did you contact the dealer about maybe splitting the cost or something? Of course if YOU specified the specs because you thought the higher geared ratio would get better mileage, it's on you.

Just have a competent person with experience do the swap for you if you decide to do it. Unfortunately, I don't think you will recoup much by reselling the original gears.

 

Thanks for the info sliver.... I don't know why the 3.73 is not offered makes no sense to me because it was on my 06. I don't think going from 3.31 to 3.55 will do much for the MPG. The truck has about 7200 miles on it but right now the dealer has had it for 14 days trying to fix a brake problem. (Yes 14 days to fix brake problem) Who knows maybe the pulling front brake was the MPG problem.

 

Thanks for the info Lx... You are right the salesperson should have been more help. He builds hot rods and been selling for more than 20 years. I guess this mush have been the first truck he help build. I came in with a printed sheet from ford build and price. I had everything on it but NAV and sunroof at a sticker price over $59,000. Due to the fact that this sales person is most likely a member of Enthusiasts I have nothing more to say about sales. This is a small town and there is only two shops that will try a gear swap. Due to the fact that I travel a lot I need to find a Ford dealer to change out the gears, but I think only 3.73, if I do change.
Hope to get more info from this forum. THANKS

 

It gets even more interesting when you get into medium and heavy trucks. The options are endless. You can easily build on paper a worthless truck that will never run for its intended purpose in the real world. I would think light duty would be easier due to limited choices. I'm curious to see what you get after the brake issue is resolved. Let us know!