Differential swap
Our tow vehicle is a 2004 f350 with the v10 and 3.73 gears. It pulls just fine here in flat-land country, but not much of a grade is needed to make it shift down. We'll be heading out West in the near...
Forum Discussion
RCMAN46 wrote:Ivylog wrote:
Why does a tranny have gears... It's to change the gear ratios. Manually gear down and keep the RPMs up... Same going down the pass.
X2
Changing gears will not increase your horsepower period.
What is so important in pulling hills in 5 th gear with a 4+ rear gear when you can do the same with a 3.xx gear in 4 th gear?
No the overall power is not increased... but...
Most importantly, I think that the available transmission gears are effectively closer together with higher numbered axle ratios. With 4.56's as an example, the numerical jump from 4th(OD) to 3rd causes less engine rpm change than a jump from 4th to 3rd, or 3rd to 2nd, with 3.73's. In other words, the difference in transmission ratios really becomes mathematically a smaller percentage of the overall gear reduction. So with lower gears, when the transmission finally does kick out of 4th on a hill, it feels like not such a drastic change into 3rd... and it isn't.
For myself (and yourself) and many others, the swap is probably unnecessary. But for dedicated towing, a gear swap can be pretty valuable. This is especially true when one only has 4 gears to start with (4R100). They are spread pretty wide as opposed to a 5 or 6 speed. From experience, I found this to be true when I casually swapped sprockets back and forth on a vintage 4 speed motorcycle (highway vs off-road). The advantage is great enough to actually be felt seat-of-the-pants. All newer bikes usually have 6 speeds.
For a 3/4 or 1 ton gas truck, 3.73's are probably as tall as anyone might want to go, and that point represents a reasonable compromise at the OEM's best word-of-mouth maximum fuel economy, avoiding a distinct sales disadvantage. Some folks drive these "tractors" back and forth daily to work. When I picked up my "pre-owned" Excursion, the lady had to take her child-seat out of it first. The digital mpg readout said the truck was getting 6 mpg (winter, city) and it has never done better than a dismal 14 highway for me.
The trade-off to installing new, lower truck gears is a probable reduction in unloaded, or light-load, fuel economy and a significant upfront investment expense. For a 90+ percent tow duty and a planned extended ownership, lower gears may make the most sense. I'm satisfied the guys that have done this swap here, have spent a lot of time carefully considering the modification and it seems well spent to me.
Wes
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