Towing with 3:31 gears - Ford Powerstroke Diesel Forum
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post #1 of 18 Old 04-24-2011, 03:45 AM Thread Starter
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Towing with 3:31 gears

Ordered my F-250 4x4 6.7L PSD with the 3.31 gears, but now thinking I maybe should have gone with the 3.55's for towing my 5th wheel camper. My camper weighs around 11,000# and I had no problem towing it with my old 7.3L PSD but I did have the 3.73 axle on that truck. I was wondering if with the 3.31's will my tranny stay locked up like my old truck did or will it unlock and/or downshift on every hill like the gas motors do. Anyone doing much towing with this gear ratio and are happy with the tranny performance? Wish I would have given it more thought before I ordered it.

2011 Ingot Silver F250 XLT 6.7L PSD SB CC FX4 3.31 Gears


Last edited by 8upbowhunter; 04-24-2011 at 04:21 AM.
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post #2 of 18 Old 04-24-2011, 05:11 AM
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The 6.6 transmission is tied to an overdrive transmission so final drive is very different from your 7.3. You can also manually shift with this transmission too. Ford's towing specs says either will work with that load. That said, if you are or expect to be towing in the mountains, or will be towing that load on the flats 75% of the time versus running empty, I would try to change the order; otherwiosee should be fine. If mainly running with light loads stick with what you ordered and your mileage will be better.
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post #3 of 18 Old 04-24-2011, 05:31 AM
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3.31's will tow that all day and not even break a sweat. You gotta think too, you're going from 525ish ft. lbs. of torque to 800 ft. lbs.

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post #4 of 18 Old 04-24-2011, 06:01 AM
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The 7.3 had 525 lbft of torque at the crankshaft, here is the axle torque in the various gears of the 4r100 with the 3.73 diff vs the new powerstroke with 800 ftlbs of torque and 3.31 gears:

..............................................7.3 liter........................6.7 liter
rear axle torque in 1st............5300 lbft .................... 10,512 lbft
............................2nd...........3016.... ...................... 6,143
............................3rd...........1958.... ...................... 4,024
............................4th............1390... ...................... 3,045
............................5th............ n/a.......................... 2,277
............................6th............ n/a.......................... 1,774

These values are only for comparison purposes as they assume no torque loss in drive train. The 6.7 with the 6 speed has so much more torque that even with the 3.31 rear end you will be thrilled if you're comparing to a 7.3.


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post #5 of 18 Old 04-24-2011, 05:00 PM Thread Starter
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I would say that 85% of the time I will be running empty or towing in the deep south. I do make a yearly camping trip to the Smokey Mountains and eventually I would like to go out west. I guess I could live with it since it's probably too late to change my order and I don't want to wait an extra 3 weeks for it to come in. I guess the extra 275 lbft of torque should make up for the gear difference. Thanks for the replies.

2011 Ingot Silver F250 XLT 6.7L PSD SB CC FX4 3.31 Gears

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post #6 of 18 Old 04-24-2011, 07:04 PM
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Quote:
Originally Posted by 8upbowhunter View Post
I would say that 85% of the time I will be running empty or towing in the deep south. I do make a yearly camping trip to the Smokey Mountains and eventually I would like to go out west. I guess I could live with it since it's probably too late to change my order and I don't want to wait an extra 3 weeks for it to come in. I guess the extra 275 lbft of torque should make up for the gear difference. Thanks for the replies.
You won't even know it's back there.

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post #7 of 18 Old 04-24-2011, 08:01 PM
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I also went from a 7.3 (3.73 ratio) towing a 11000 pound 5th wheel and a horses trailer weighing around 8000 to 9000 pounds depending on how many horses loaded. I have towed the horse trailer around 10 times this spring and with tow haul it is a pleasure. You cannot really tell that the truck is working at all. I am very happy with the 331 ratio. Fairly soon We will start using the 5th wheel and I am confident it will do it well with the 3.31 gears. I really like the exhaust brake so far.
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post #8 of 18 Old 04-24-2011, 09:15 PM
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The 3.31 is a whole different animal! I tow a 12,500 lb, 33ft trailer and most of the time forget it's even there except for when I see it in the mirror.
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post #9 of 18 Old 04-24-2011, 11:24 PM
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8upbowhunter,
For the uses you describe I would not change the order- even if there were no time delay.

John D
2011 F450
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post #10 of 18 Old 04-25-2011, 01:05 AM
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My toy hauler wieghs about the same empty 37' 11500lbs cant even tell its there. I pulled my buddies 40' its 16k empty to vegas still had plenty of power the differents is in the fuel mileage it cut in about half. I also have the 3:31 and on top of that have 35" tires so I wouldnt worry about. Enjoy your new truck
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