24 F350 Rear Gears

[pacbj]

Looking to buy a new F350 SRW. I currently have a 18 F250/6.7/3:55 rear end, 6 speed auto. Tows the high country like a freight train. I’m seeing a lot of the new trucks with 3:31’s in them with the 10 speed tranny. Wondering if anyone has any experience with the higher gears and your thoughts. Thanks in advance

[NH_Bulldog]

The F350 with the SO and HO 6.7 comes standard with the 3:31, but you can get 3:55 or with a gasser also 3:73 and 4:30. I think the 3:55 is a great all-around gear for a diesel, especially the HO and that's what I would suggest. The 3:31 is for people who don't tow heavy loads and want better unloaded fuel mileage. My 7.3 gasser came with the 3:73 and 10-speed transmission and although not really comparable to the diesel, I have never had an issue towing any 5th wheel, gooseneck, or bumper pull trailer in the mountains or anywhere else.

[jfk69]

I agree with the above comments, the 3.73 (or 3.55) is a great rear end. Can’t go wrong with either with the 10 speed tranny.

[JRTJH]

Originally Posted by pacbj

Looking to buy a new F350 SRW. I currently have a 18 F250/6.7/3:55 rear end, 6 speed auto. Tows the high country like a freight train. I’m seeing a lot of the new trucks with 3:31’s in them with the 10 speed tranny. Wondering if anyone has any experience with the higher gears and your thoughts. Thanks in advance

If you intend to equip the new SRW F350 with the 6.7L diesel, either standard output or high output version, the only available axle ratios are 3.31 or 3.55. You can option for electronic locking axles, or the 3.31 open non limited slip axles. The 3.73 and 4.30 axles are not available with the diesel engine. If you opt for a DRW F350, you can get a 4.10 limited slip axle ratio which is not available in diesel equipped SRW trucks.

I have a 2015 6.7L with the same 6 speed transmission you currently have. My truck is equipped with the 3.31 gear ratio. I tow a 10K GVW fifth wheel and either a 3000 pound boat or a 3200 pound motorcycle trailer behind the fifth wheel on most trips. That's towing the equivalent of a 13-13.2K trailer.

My "version" of the 6.7L has 440HP/950 ftlb torque. I have never had any issues maintaining the speed limit anywhere, on any climb in the mountains or any "engine braking" on the decent of any of those passes. I do, typically downshift to 5th gear and lock out 6th as soon as the truck "downshifts at the start of a steep climb". Otherwise, I don't recall any "downshifting" that has occurred to keep the truck speed up. Usually, the turbo pressure will increase and the truck "just keeps pulling without breaking a sweat" and without downshifting.

While I have no specific experience towing with a 2024 F350 with either the 3.31 or the 3.55 gear ratios, I'd suspect that with the 10 speed transmission, there's no reason to expect a decrease in performance at maximum trailer weight with either ratio. I have talked to a couple of people at the local Ford dealership and they seem to "lean toward what's on the lot" rather than having any "factual or data based evidence to share". Honestly, the people who work there don't have any experience with heavy fifth wheel towing, so I discount any "3.31/3.55 comparisons they might offer as part of the sales pitch".....

I will add that towing or solo, my best fuel performance is about 2300 RPM. The speed limit on Michigan's interstate system is 75MPH outside congested areas. With my 3.31, my RPM at 75 is about 2150. My buddy's 2016 truck with the 3.55 gear ratio at the same speed runs about 2450 RPM. So, neither of us have "the ideal RPM for ideal fuel economy at 75MPH.

[rhagfo]

Originally Posted by pacbj

Looking to buy a new F350 SRW. I currently have a 18 F250/6.7/3:55 rear end, 6 speed auto. Tows the high country like a freight train. I’m seeing a lot of the new trucks with 3:31’s in them with the 10 speed tranny. Wondering if anyone has any experience with the higher gears and your thoughts. Thanks in advance

Now that it seems that 3:31's or 3:55's are the only ratios available i will add to that. We had a 2001 Ram 2500, 5.9 CTD, 5 speed manual, and 3:55's, I did add a small chip. with that truck we pulled a 5th wheel at a bit over 13,000# and could hold 55 mph on hills. I believe that the 10 speed will make the 3:55's work fine with either option.

[JBM3M]

We bought a '23 F350 SRW long bed, with 6.7 and the 10 speed last Oct. I traded a 2000 F350 7.3 manual, blah blah. This new truck is so far beyond the old F350 which was the best you could get back then with the 7.3. I was very hesitant to get the 6.7.
Well, once broken in we did a fairly long RV trip in the winter when the big storm hit up here. I was nicely blown away with towing the 5er. I can go on an uphill ramp to freeway and be at traffic speed before I merge, which is something the 2000 did not manage. We are going over Deadmans Pass this weekend and will get to see how it does on those uphill pulls, but I don't expect any problems.

The gearing is excellent for towing, plus the truck has a "tow" mode along with normal, eco, 4x4, and off road modes...pretty cool. Cab is roomy, comfortable, and quiet...even the cat is happier.
You cannot go wrong getting this vehicle. Make sure you get the tow package and the snowplow/camper package to improve your experience. These puck hitch systems in the bed are very nice. (Tow package gets you a class 5 bumper hitch and the bed puck system for the hitch and a s5th wheel ball.

Fuel mileage has been awesome too. 20 on highway unloaded, 12-14 towing.

Oh, and don't forget the engine brake. Love it.

Can you tell I love this truck?

[JRTJH]

Originally Posted by JBM3M

We bought a '23 F350 SRW long bed, with 6.7 and the 10 speed last Oct. I traded a 2000 F350 7.3 manual, blah blah. This new truck is so far beyond the old F350 which was the best you could get back then with the 7.3. ...

What gear ratio does your new truck have? 3.31 or 3.55 ???

[Dipstick]

That's what I love abot thse fords 12 -15 mpg pulling, it's a great world .

[JBM3M]

I dont know ratio but the off road package defines which set as I remember. iI had no choice, it was what was on the lot that fit our needs. Not sure how to tell what I have.

[JRTJH]

Originally Posted by JBM3M

I dont know ratio but the off road package defines which set as I remember. iI had no choice, it was what was on the lot that fit our needs. Not sure how to tell what I have.

The FX4 Off Road package requires either the 3.31 or 3.55 electronic locking rear axle, so the ratio can be either/or. If you have access to your window sticker, the axle ratio and axle type (locking or limited slip) is listed in the Optional Equipment/Other column in the main body of the window sticker.

The axle ratio is also listed on the "build decal" located on the driver's door panel next to the payload sticker. The axle code on that decal will need to be looked up by code to determine the axle type. But it's listed "written out" on the window sticker.

Here's a picture of where it's at:

[JBM3M]

might be a few hours I have a comittment to complete first.

[JBM3M]

Well the window sticker is among the missing, but if it helps, at 70mph in tenth gear is 1600 rpm, so not sure on gear ratio, sorry. Gosh I love this truck, came over Deadmans, which is no biggie going West, except for being able to manually change gears and utilize the engine brake to it's best performance. Heck I am still learning. Still from home almost all the way is uphill and got 12.7 mpg

[JRTJH]

What is the axle code on the information decal on the driver's door pillar? The decal is located next to the payload sticker. With that 3 digit code, we can determine which axle and axle ratio is in the truck. That information would make your description relevant for the OP, since then he will have your experiences with a specific axle, and that will give him 1/2 of the comparative assessment he is looking for.

[sourdough]

The new trannies with lots of gears are such an improvement. One needs to remember that the transmission with 10 speeds is then limited/helped by the rear axle ratio. Here is a link to the transmission ratios:

https://gearsmagazine.com/wp-content...7.39.22-AM.png

Note that gears 8-10 are overdrive gears (lower than 1:1). They don't do much when towing a trailer because the truck will want "more power" to pull. The "power" will then come from the ratio in the axles - the lower numerically in the axles the deeper the tranny has to dig into its ratios to "go". 1600 rpm at 70....I don't know what that would equate to. Did you have a load or just the truck? Like was mentioned the higher the axle ratio the better the towing experience but less gas mileage when empty. Your VIN may tell you what the ratio is but I'm not familiar with Ford "stuff" anymore these days.

[JBM3M]

That was towing. See sticker

[JRTJH]

Originally Posted by JBM3M

That was towing. See sticker
Attachment 46455

The Ford super duty axle code 3j is 3.55 Electronic Locking axle. The Electronic Locking axles are both "optional at extra cost on the XL, XLT and Lariat lines.

[GlasNav]

3.55 Limited Slip

[GlasNav]

Originally Posted by JRTJH

The Ford super duty axle code 3j is 3.55 Electronic Locking axle. The Electronic Locking axles are both "optional at extra cost on the XL, XLT and Lariat lines.

Thought it had to have an X in front of it for locking?

[JRTJH]

Originally Posted by GlasNav

Thought it had to have an X in front of it for locking?

ALL Ford SuperDuty axle codes start with "X".. On the decal, the "X" is omitted since it's redundant information.

Here's the actual Ford Specification/availability data from the Build Guide:

[GlasNav]

Originally Posted by JRTJH

ALL Ford SuperDuty axle codes start with "X".. On the decal, the "X" is omitted since it's redundant information.

Here's the actual Ford Specification/availability data from the Build Guide:

John: This spurred my interest, so if I understand correctly the W3B indicates 4x4, and when 4x4 is selected the differential locks.