3.55 for 7.3L or...?

[ert01]

I have a 4x4 e350 with the 7.3 (2002), 3.55 gears and 285/75R16 tires (33").

I am currently near the end of a 3 week trip where I flat-towed my Jeep XJ (4500lbs approx) for the first half of the trip and I've left it behind for the second half.

My verdict is that the 3.55's are only good when driving on flat terrain, towing nothing. They get good mileage in that scenario, but for every other type of terrain and for ANY towing, they are sub standard. I will likely re-gear to 4.10's after I get home. This was my first trip towing and it'll be my last towing with the 3.55's...

I've been driving all over BC and Vancouver island and it is shameful to be passed by loaded semi trucks on the highways uphill. The whole reason I bought this 7.3 was for the capacity to tow and it doesn't do so well with the current gears.

[Bbasso]

Let me be clear, I was not suggesting the OP keep his 3.55 but if he does... get a transmission cooler.

Of course I'd recommend 4.10 for a lift, possibly 4.56 if the terrain is challenging. Let the gears work for you, not against.

Might be common knowledge for many but the 4R100 needs to stay well under 215 deg to be happy and live a long life.
Anything above and you risk failure quickly.

[boywonder]

As another data point, I have a 4WD, 5.4L, 4" lift and 3.73's. The only thing I occasionally tow is a small motorcycle trailer.

I live CA and frequently travel around CA and over to Utah; the 3.73's will downshift on anything more than mellow uphill grades at highway speeds. I'm happy with my setup but I don't think it would work well pulling a trailer of any substantial size. I imagine the behavior with a diesel would be different due to the low-rpm torque difference.

[E350]

ert01: Thanks for your post!

How much for your front axle 3.55 ring and pinion?

[MtnVan]

My 7.3PSD E350 Quigley 4x4 with 295/75/16 tires (closer to 33.5") is running 3.55 gears. I use it to pull a loaded horse trailer, do flat road trips, and crawl up class 3 trails. What makes it run strong and still pass car and trucks when loaded with gear and people is working around the weak factory tune from Ford. My recommendations for the 7.3PSD (regardless of gearing):
- bigger exhaust from the turbo back
- tuning software dialed in for a van which has no intercooler (most tuners only have F series tunes)
- gauges to watch temperatures
- maghytec tranny pan (26 quart capacity) and differential cover
- larger trans oil cooler
This set-up pulls hard, cruises 85mph at 15mpg, and crawls smoothly without overheating. But I always pull the horses slowly…

No matter what you do - enjoy that 7.3PSD!

[Vindisl]

Thanks for your input everyone. Very much appreciated! The following advice are especially useful:

1) Transmision cooling: will plan on a large cooler and temp gauge.

2) Fuel Tank Delamination: NO symptoms yet. Have never used biodiesel, additives or offroad diesel. Planning on installing a new larger capacity tank. Losing 7-8 gals of OEM tank capacity is necessary for 4x4 conversion I was told - so might as well bite bullet and get large tank.

3) Shame: No - I don't want loaded semi's shaming me neither! No way! The trick to get the original balance of performance vs. fuel economy is possibly to try and get the wheel diameter vs. gear ratio as nearly OEM as possible. ( Discounting, for the moment, variables such as extra weight and poorer aerodynamics ). OEM 30.5"/3.55 ratio is closest to 35"/4.10. Which leads right up to the next point!

4) Looks: Lifting the van 4-6" and putting 35" rubbers would probably make it look awesome. So be it! If I am changing the gear ratio and, it is a requirement to go bigger than 16", I might as well as well go all the way to 18"X35"/4.10.

This is fun! Thank you for playing.

[ert01]

Originally Posted by E350

ert01: Thanks for your post!

How much for your front axle 3.55 ring and pinion?

Not sure you'll want them... I'm in Canada so shipping could be a pig. I have a kingpin 60 in the front of my van so you'd also need to confirm that they'd work for you.