New Truck: Differential Choice

[LaunchnRetrieve]

If a 3.15 differential is rated to tow at my weight needs, is there a reason to get the 3.73 which tows even more? Will I notice a difference in towing between the two diffs if the lower one is rated above my needs?

[dodge_guy]

If getting something to tow anything significant, always go with the lower gear (numerically higher). The fuel savings is so insignificant, that it isn't worth it.

[Chad_Brooks]

ynotTurbo, what rpm are you seeing at 70mph? We just traded for a 2016 Ram 3500 CTD 4X4 with the Aisin and 3.73 gears. I just picked it up yesterday and I am really impressed so far. It looks like we are around 1900 at 70mph in 6th and around 2200rpm at the same speed in 5th.

[YnotTurbo]

I always get as much gearing as possible. 4:10 is my only choice,,, but if I could not get that, I would have the 3:73's. I still get 16 mpg empty with my Ram. I get between 7-11 when towing my fiver. I honestly did not buy my truck for the fuel mileage. That is why I added a 50 gallon aux fuel tank in the bed.

[LaunchnRetrieve]

lenr wrote:
Good Grief 2! The Duramax usually (always?) comes with an Allison 1000 transmission that has a top gear of .61. With a diesel the Ford 140 transmission has a top gear of .67. So, an Allison with a 3.73 rear is functionally equivalent to a Ford with a 3.40. Ford offers 3.31 and 3.55--but, with with any "heavy" options Ford forces you into 3.55.

IMO the reason that ones sees so many 4x4 in tow vehicles is that one sees a lot of diesel engine tow vehicles. The heavy diesel engine kills the front to rear weight ratio giving pretty bad traction on slick surfaces. I rarely use 4x4 in my F-350, but I would not be without it.

To the OP--I still strongly recommend the 3.73 because peak torque for your engine is 2500 RPM and th3 3.73 will get you closer to that engine speed in a higher gear. However, the transmission will shift to whatever gear is necessary to achieve the HP necessary to do the work that you're trying to do. If you don't want the Max Tow package that will likely be stuck with the 3.73 ratio, then I suggest at least the 3.55 ratio.

Thanks for the technical advice. Appreciated.

[lenr]

Good Grief 2! The Duramax usually (always?) comes with an Allison 1000 transmission that has a top gear of .61. With a diesel the Ford 140 transmission has a top gear of .67. So, an Allison with a 3.73 rear is functionally equivalent to a Ford with a 3.40. Ford offers 3.31 and 3.55--but, with with any "heavy" options Ford forces you into 3.55.

IMO the reason that ones sees so many 4x4 in tow vehicles is that one sees a lot of diesel engine tow vehicles. The heavy diesel engine kills the front to rear weight ratio giving pretty bad traction on slick surfaces. I rarely use 4x4 in my F-350, but I would not be without it.

To the OP--I still strongly recommend the 3.73 because peak torque for your engine is 2500 RPM and th3 3.73 will get you closer to that engine speed in a higher gear. However, the transmission will shift to whatever gear is necessary to achieve the HP necessary to do the work that you're trying to do. If you don't want the Max Tow package that will likely be stuck with the 3.73 ratio, then I suggest at least the 3.55 ratio.

[LaunchnRetrieve]

Chuck_thehammer wrote:
I am old school... never considered a turbo V6 as a towing rig. Sorry.

in that case... 3.73 or ask for a 4.30

still No mention of weight or size.

my question.. Why are so many tow rigs using 4x4... you tow a trailer in marshes.

I haven't had 4x4 before, but lost a couple of months of boating to the drought because I could no longer launch with 4x2 when the water level dropped below the end of the launch ramps, but 4x4s could still launch. Drought, or no drought, 4x4 would give me peace of mind on steeper slimier launch ramps.

Also have experienced steep dirt roads with tight approaches in camp ground that had a lot of wheel slippage trying to tow out.

Other than that I'm not excited about getting 4x4.

The size is my 18 foot ski boat or my 25J Prowler 2003 (trailer is stored at campground so I can't be certain of weight right now). If I recall correctly the trailer is 5000 lbs dry weight.

[rhagfo]

Interesting no mater the engine or transmission 3.15 seems ver tall. Now that the F150 comes with a 10 speed auto it might work there depending low the lower gears are in the transmission.

[KD4UPL]

Sport45 wrote:
With single rear wheels the Duramax only comes with a 3.73. There's got to be a reason for that...

Forget the single rear wheel part. Durmax = 3.73 period.


As for why the 4x4 trucks for towing? I can't afford a towing only truck. Mine has to haul firewood, drive in the snow, make it to muddy construction sites, and have some resale value when I'm done with it. Around here it's hard to give away a 2wd truck. I use my 4wd at least once a month.

[Chuck_thehammer]

I am old school... never considered a turbo V6 as a towing rig. Sorry.

in that case... 3.73 or ask for a 4.30

still No mention of weight or size.

my question.. Why are so many tow rigs using 4x4... you tow a trailer in marshes.

[time2roll]

Deleted

[Sport45]

With single rear wheels the Duramax only comes with a 3.73. There's got to be a reason for that...

[jmtandem]

Another vote for 3.73.

[Farmerjon]

3.73. My 2000 and 2015 F350 diesels have 3.73 gears and I'm very happy with both.

[lenr]

Good grief not enough information! Final ratio depends on the top gear ratio and tire size. In Ford land, options and final ratio are usually tied together. In an F-150 in past recent years the max tow package got you a 3.73 and a 3.73 got you a max tow package. In fact until I complained to Ford about it a few years ago, the only way you could get a max tow package in the on line build a truck tool was to first select a 3.73. Suggest the OP get the 3.73. Higher numeric ratios do not hurt gas mileage as much as it hurts diesel mileage.