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2020 Ford F350 6.7 4x4 gearing selection

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  • 2020 Ford F350 6.7 4x4 gearing selection

    OK folks. I stumped my local Ford sales person - not hard to do. Anyway I am looking at getting a 2020 F350 SRW probably after the first of the year. My current 2004 F350 dully king ranch withe 6.0 makes 325 HP and 560 Ft-Lbs of torque. I am running 4:10 LS gearing in the rear end, Trans is the 6 speed. It pulls my 220RK fine and my previous 12K trailer OK before. Could use a bit more power on steep grades for towing both. Fuel mileage - 16 solo and 10-12 towing.

    Now the 2020 6.7 is producing 475 HP and 1050 FT-Lbs or torque and has the new 10 speed behind it, Gearing on the 10 speed seems to be secrete, except the top 3 gears are OD.
    Rear end has to gears available. Either 3.31 or 3.55. Looking down the road I will probably stay on the smaller 5er side, but for this post assume 12K max on trailer.

    So for mountain towing and keeping up with and for folks (not impeding traffic) do I go with the 3.31 or go with the 3.55 which is where I am leaning as it would put less tress on things and have better gearing for down grade control. Solo MPG is important, but I am not finding much information on the expected differences.

    Hopefully there is an informed gear head that can enlighten this engineer.

    Thanks
    Keith

    PS what is strange now a days is I cant find a towing guide that you input your trailer specifications and it tells you what gearing to get. Back in 04 Ford had that available at the dealers .- no more
    Last edited by Yoda; 11-16-2019, 06:46 PM.
    2018 Reflection 150 Series 220RK 5th whee, Star White 2022 F350 King Ranch CC Long bed (HAL) (CCC 4062lbs), B&W 25K OEM Companion,. SteadyFast system, Trailer reverse lights, rear receiver spare tire holder, storage tube, sumo springs, Victron MultiPlus 12/120/3000, Solar, Custom 6K axles upgrade, and other modifications.

  • #2
    Yoda,

    The final drive ratio is tied to the GCVWR where the differences between a 3.31 and a 3.55 is not all that much different. With over 1k ft lbs of torque you will not have an issue with a 12K trailer. If you know what size trailer you will never exceed, you can make the choice of max tow based on this load and payload where the final drive will then allow for better solo fuel economy. Some folks may advise on getting the largest truck possible. If you know where your headed, you can make a sound decision on a truck and save on fuel and wear.

    Jim

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    • #3
      I am not an engineer, just have pulled many trailers with various trucks. I would go with the 3.55. My 97 ford 7.3 had a 3.73 if I remember correctly and would pull anything I put behind it. I wish I had that ratio now. My 2017 F250 diesel has a 3.55 and does fine pulling a 14,000 lb trailer but at times seems a little sluggish. I would give up the fuel mileage for more pulling power.
      2017 F250 Diesel Superduty SRW SWB
      2020 Solitude 310GK-R

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      • #4
        I'm not a gearhead by any stretch of the imagination, but I've done a ton of reading on this subject. My '17 DRW has 3.55 gears. On the '17 DRW 4.10s were an option.

        Look at the chart below (from the '17 model). The capability difference between the gears for my truck is GVWR. So what does that mean? The 4.10s are meant to get really heavy loads moving. The 3.55s were for "normal" loads.

        The 4.10 is still an option for the DRW (not on the SRW) which makes sense based on the size of the load being carried and towed.

        Click image for larger version

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        The Ford document for the '20 is here: https://www.fleet.ford.com/resources...uide_Sep26.pdf

        Look at page 24 for the F-350 SRW numbers and you'll see the chart like the one I pasted in below. There's no numerical difference in capability from the 3.31 to the 3.55. But it makes sense that the 3.31 truck will downshift before the 3.55 on hilly roads while towing. (Don't forget the chart above is for a DRW, the chart below is an SRW so don't try to compare number-to-number.)

        Once you start looking at what's on the lot you'll discover what "most" people are buying. I had a '17 F-250 SRW (before the truck I have now) and every single one on a dealer lot had the 3.55s.

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        Forum moderators are not GD employees--we are volunteers and owners presumably just like yourself. Unless specifically mentioned otherwise, we have nothing to gain should you choose to purchase a product or engage a service we discuss on this forum.

        2017 Ford F-350 DRW, '19 315RLTSPlus

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        • #5
          Howard you went and did it again. Thanks

          I have the guide https://www.fleet.ford.com/resources...uide_Sep26.pdf that you posted but it does not give you the butt factor. In years past the rule was get the lowest gearing (highest numerical number like 4:10) you could. Now with the high HP and torque out there its not the case. But sometimes its best not to muscle through things. I have broken a lot of drive line parts thinking a little more power would do it in my 4-weeling days.

          Now by butt factor I am talking like pulling away from a stop light. I want to get going, not wait on turbo lag and then get rolling or pulling the I-70 grade on the west side of the tunnel. I don't want to be holding up traffic and still have a bit of extra power to merge or pass. Or my best need is the passing lane is ending, you are still in the right lane having let folks by needing to merge left at the end of the lane and some idiot tries to pass you at the last instant, just when you must move over as the lane has ending and your on the shoulder hoping the oncoming traffic does the same. Happened more than once.

          Now do I need the Binford 2000? - probably not. Its been a while since I was truck shopping. I have driven all 3 brands of 19 models and will do the same with the 2020's. Right now the Ford F350 interior and seat fits me better (8 way power). you need to be a tall lean Texan for the dodge. be of good lean build for the GMC and Chevy (there is a difference between them) and the Ford just fit. I am a short round dude (short arms, long torso and short 28" inseam legs) and the current Ford seat fits me. Dodge lumbar was too high with little side support (truck rattled too). Chevy I had trouble getting a comfortable fit with the peddles (GMC Denali trim level was exception with an OK fit but $$$$$$$$.)

          This will probably be my last forever truck for when both of us are retired (I may even wait a year or so) I guess the engineer in me wants to crunch numbers. Sooner or later the 10 speed ratios will be out so I can compare to the 6 speed and my current gearing. I guess that makes me an official gear head

          I am bummed about the 4x4 esof - my 04 KR has the manual 4x4 system with the locking hubs. I know for sure when its locked in. My 03 that I lemon-ed had the esof and it never worked correctly - had to be moving for it to engage, so if stuck you were well .s out of luck. I have been told the current ESOF works.

          I know I am over engineering this...so back to my corner

          Thanks everyone
          Keith
          On edit from the other place
          Last edited by Yoda; 11-17-2019, 01:14 AM.
          2018 Reflection 150 Series 220RK 5th whee, Star White 2022 F350 King Ranch CC Long bed (HAL) (CCC 4062lbs), B&W 25K OEM Companion,. SteadyFast system, Trailer reverse lights, rear receiver spare tire holder, storage tube, sumo springs, Victron MultiPlus 12/120/3000, Solar, Custom 6K axles upgrade, and other modifications.

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          • #6
            Yes you are correct. Page 25 of the guide has 5th wheel. Either gear set will work. Wish I knew how to get the chart in here.
            2018 Reflection 150 Series 220RK 5th whee, Star White 2022 F350 King Ranch CC Long bed (HAL) (CCC 4062lbs), B&W 25K OEM Companion,. SteadyFast system, Trailer reverse lights, rear receiver spare tire holder, storage tube, sumo springs, Victron MultiPlus 12/120/3000, Solar, Custom 6K axles upgrade, and other modifications.

            Comment


            • #7
              Yoda,

              From your description it looks like the 3.55 is the choice, since you mention towing in the mountains. Odd that Ford would not just pick the 3.55 as a single selection anyway. Turbo lag is pretty much a thing of the past where there is some measurable lag but its very short. Trucks today are torque managed off the line, so it should not be possible to destroy parts.

              Jim

              Comment


              • #8
                Originally posted by MidwestCamper View Post
                Yoda,

                From your description it looks like the 3.55 is the choice, since you mention towing in the mountains. Odd that Ford would not just pick the 3.55 as a single selection anyway. Turbo lag is pretty much a thing of the past where there is some measurable lag but its very short. Trucks today are torque managed off the line, so it should not be possible to destroy parts.

                Jim
                "it should not be possible to destroy parts"

                Jim - you really know how to make me laugh - I break everything without even trying, especially with a sawsall. Its good the know modern technology helps manage things, but that means computers and they get expensive. Sometimes I wish I had my old 80 Scout II with no computer. Just points, plugs and ignition wires and maybe a fan belt to wear out. No computer - true plug and play. And I managed to destroy a LS diff (split it in two) and twist off a drive shaft, and break springs.

                But you are correct - looking like the 3.55 is the way to go.

                Thanks Keith
                2018 Reflection 150 Series 220RK 5th whee, Star White 2022 F350 King Ranch CC Long bed (HAL) (CCC 4062lbs), B&W 25K OEM Companion,. SteadyFast system, Trailer reverse lights, rear receiver spare tire holder, storage tube, sumo springs, Victron MultiPlus 12/120/3000, Solar, Custom 6K axles upgrade, and other modifications.

                Comment


                • #9
                  Yoda,

                  Understand. I have a 1967 Chevelle SS 396 and a 45 Willys MB where they are very easy to understand.....and break. Today we have abuse codes and can also detect if aftermarket calibrations are present. Its actually really hard to tear up a modern vehicle these days. But not impossible if not maintained.

                  Jim
                  Last edited by Guest; 11-17-2019, 01:14 PM.

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                  • #10
                    An anecdote to ease your mind:

                    We went across the country, last year (Birmingham to Seattle and back) towing a 9000# 2950RL with our 2017 F-350 SRW PS.


                    I thought the Tetons and Rockies were supposed to be white-knuckle-only drives.

                    Wrong!

                    Put 'er in Tow/Haul mode, turn on the Automatic Engine Brake, set the cruise control and relax.


                    Off the line?

                    I have outrun economy cars on the entrance ramp to the highway towing the rig!


                    3.55 is plenty.
                    Last edited by Najataagihe; 11-30-2019, 10:42 AM.

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