Changing rear end gears

[JExpedition07]

mechanical advantage is still mechanical advantage. No matter how you swing it, its still an advantage.

Its no different than lifting a 100lbs next to your body vs 3 feet away at arms length.

Anything can compromise, like the transmission and such, but its always just that, a compromise......

Yep, I recall someone ran the numbers by the torque multiplication on the 3rd gens. A 5.4 V8 with HD tow (3.73) was putting down quite a bit more torque than a non HD-tow EcoBoost with the base 3.15s at both engines peak powerband. Despite the advertised crank rating the newer one was weaker on twist at the tires was the point proving rear end still is in the game. Rear end always matters. Obviously HD tow ecoboost was the best by far.

 

[Deadman]

So they give you the tow pack with the package, but charge you more for the 3.73's. lol. WTH

 

[Rick Fossen]

So should I take off from a stop in 4L then?

Interesting idea, does anyone have any insight on starting in 4A just to get things moving and then switching back to 2wd when towing close to max with a Non-HDT? Would relieve some pressure on the rear I would think?

 

[wakeboarder]

That’s the same chart for the 18-20’s as well. In 2021 they split the eSLD out of the package but this chart and brochure still reference the HD tow package including the eSLD. Window stickers are all over the place. Some have the HD tow and no charge for eSLD. Some have the tow and eSLD no charge and some charge for both. I would be pissed if I ordered the HD tow and later was told I need the 3:73’s. Or could just order the HD tow and save $1100.00 and get the eSLD for free. But if the 3:73’s are limited to 6K on some models it means the radiator is the bigger advantage like I have been saying all along.
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The 2019 chart is different than the 2021 chart. The 2019 is below. I also put the 2021 axle chart.
Your screenshots show and the charts indicate that all HD tows have the 3.73 gears.
It is possible to get 3.73 gears without HD tow. A 4x4 with eLSD will get 3.73.
I think it shows that eLSD is not important for HD tow. It does not prove or prioritize the rest of the features like 3.73 gear ratio and radiator.

 

[ExplorerTom]

Interesting idea, does anyone have any insight on starting in 4A just to get things moving and then switching back to 2wd when towing close to max with a Non-HDT? Would relieve some pressure on the rear I would think?

Only if you’re getting wheel spin will 4A do anything.

And going to 4hi would probably cause adverse driveline binding if you’re not spinning.

Just leave it in 2hi (or 4A) and tow away.

 

[Fozzy]

The 2019 chart is different than the 2021 chart. The 2019 is below. I also put the 2021 axle chart.
Your screenshots show and the charts indicate that all HD tows have the 3.73 gears.
It is possible to get 3.73 gears without HD tow. A 4x4 with eLSD will get 3.73.
I think it shows that eLSD is not important for HD tow. It does not prove or prioritize the rest of the features like 3.73 gear ratio and radiator.
View attachment 42360 View attachment 42361

So with the HD tow you get the 3:73’s and no eSLD? Open diff?


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[wakeboarder]

So with the HD tow you get the 3:73’s and no eSLD? Open diff?


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Yes and yes. eLSD is a separate option that is only available on the 4wd’s. This applies to the 2021’s.

 

[Fozzy]

Yes and yes. eLSD is a separate option that is only available on the 4wd’s. This applies to the 2021’s.

I wish they made it more clear to the customer. If I had the taller gears it wouldn’t bother me at all. But I use the diff lock all the time. With how low Lake Mead and Lake power are this year I will need a front locker as well.


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[X BRONCO OWNER]

Checking 2018 expedition used rear diff listings on ebay i found that some are listed as a 9.75 inch rear end and some are an 8.8 inch rear. Does anyone have more information on this?

 

[wakeboarder]

Checking 2018 expedition used rear diff listings on ebay i found that some are listed as a 9.75 inch rear end and some are an 8.8 inch rear. Does anyone have more information on this?

Looking at differentials for the 2019 on parts.Ford.com, the 3.15 gear ratio gets the 8.8. The 3.31 and 3.73 get the 9.75.

On a side note, I was surprised to see that for part 4209, it list 3.31 and eLSD as an option. Is that what the FX4 without HD tow get?