2019 F350 SRW axle
#1
11-15-2018, 08:28 AM
#2
11-15-2018, 08:50 AM
It is really a matter of personal choice. I opted for the slightly better mileage of the 3.31. Coming from a 5.4 Expedition, I figured 925 ft-lbs through a 3.31 was more than enough (and it is), and did not see a need for the 3.55.
The locker is a must. It gives you 3 wheel drive when you need it, With the open diff, you are only ever sending power to 2 (one front, and one rear).
The locker is a must. It gives you 3 wheel drive when you need it, With the open diff, you are only ever sending power to 2 (one front, and one rear).
#3
11-15-2018, 08:59 AM
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I chose the 3.55 because I pull frequently through the Rocky Mountains. A pass at 11,000' elevation is not unusual. My bumper pull trailer has a GVWR of 11k. I wanted the drivetrain to have the easiest time pulling up the mountains. Would I be able to tell the difference between 3.31 and 3.55? Probably. Am I worried about the MPG? Nope.
#4
11-15-2018, 09:09 AM
I’ve had both. My 2017 F350 Lariat SRW Diesel had a 3.55 and my current 2019 F350 Lariat SRW Diesel has a 3.31. Both with e-lock rear. I cant tell much difference and I tow a 14000 lb 5th wheel 25% of the time.
Being i ordered with 18” tires, in order to get a 3.55 I would have needed to order HD front springs, camper pkg or snow plow pkg. which I didn’t want. With 20” tires you can order either rear without a HD front springs.
So bottom line, with 20” tires I’d probobly order 3,55 e-locker. With 18” tires I’d order 3.31 e-locker. If I was snow plowing then I’d order snow plow front springs and 3,55 e-locker.
At 65 MPH the RPM on my 3.55 was about 1,600. On the 3.31 it’s about 1,500.
#5
11-15-2018, 09:37 AM
I still, after all the threads about 3.31 or 3.55 (specifically with 6.7L) don't get why anyone would be worried one way or the other. The amount of torque being delivered is so ridiculous that gearing - especially with a very minimal difference between 3.31 and 3.55 - I just can't see how there's a "wrong" answer.
For what it's worth, I ended up with 3.31 w/e-locker and 18" wheels. I plan to tow a 5th at some point, and I've towed (previous diesels include Ram 2500 and 1500 EcoDiesels) all over the Sierras. I guess my point is, there's a lot of other stuff to decide that will drive you nuts, but don't see 3.31 vs 3.55 when we are pushing 930+ lb/ft as one of them lol.
For what it's worth, I ended up with 3.31 w/e-locker and 18" wheels. I plan to tow a 5th at some point, and I've towed (previous diesels include Ram 2500 and 1500 EcoDiesels) all over the Sierras. I guess my point is, there's a lot of other stuff to decide that will drive you nuts, but don't see 3.31 vs 3.55 when we are pushing 930+ lb/ft as one of them lol.
#7
12-02-2018, 08:06 AM
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#10
12-02-2018, 01:59 PM
E-Locker, no brainer, I never had a Limited Slip that I was happy with, also Limited Slip has a life span, in my experience. 3.55 is a great gear with the torque the 6.7 has, but I would go for the 3.31 unless I was towing heavy all the time. The "effective" gear ratio of 3.31 with 275/70/18 is 3.14, with 3.55 it is 3.37.
#11
12-02-2018, 06:51 PM
Fleet Mechanic
If you don't get the e-locker, you don't get limited slip. You get an open diff. It will act like a good limited slip though due to the electronic traction control system.
That said, I got the e-locker because it just wasn't that much added cost. I doubt I'll ever need to use it. I got 3.55 gears because of my 20" wheels and desire to pull a 10-12,000 5th wheel later on.
That said, I got the e-locker because it just wasn't that much added cost. I doubt I'll ever need to use it. I got 3.55 gears because of my 20" wheels and desire to pull a 10-12,000 5th wheel later on.
#12
12-02-2018, 09:30 PM
Cargo Master
#13
12-03-2018, 01:53 AM
Laughing Gas
#14
12-03-2018, 10:52 AM
#15
12-03-2018, 01:20 PM
Fleet Mechanic
I think that's a result of the 3.55 ratio only being available with the heavy service front springs, camper package, or 20" wheels. A 4x2 doesn't have a smaller front axle diameter. It doesn't even have a round front axle that you could measure the diameter of. The smaller GAWR just reflects the spring rating as equipped.
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