I've found a bunch of info on this site already - thanks. In looking at a few different trucks I am seeing different options for tow packages and corresponding axles. I've used this guide :
https://www.fleet.ford.com/showroom/...07_default.asp
but still have a few questions. I'm looking at a 5.4L supercrew, 2wd. Most options I see have the 7050 tow package and a 3.55 axle.

- i see the different axle ratios of 3.55, 3.73 and 4.10. What the heck is it a ratio of and/or to?
- i see for that model the 3.55 versus the 3.73 bumps my towing from 8500 to 9500 pounds. what else does it impact - using a number of 5,000 pounds, would one tow that weight easier than the other? would one give better gas mileage and/or be 'better' on the transmisison in the long run during non-towing times?

Those are the main two questions. What I'd usually be towing would be a trailer loaded w/2 4-wheelers and gear. Short trips would be about 2400 pounds, longer trips 3,000 pounds. So 8500 pound limit is sufficient, just wondering if one is better for a truck I plan to keep a long time and put a lot of miles on.

 

i see the different axle ratios of 3.55, 3.73 and 4.10. What the heck is it a ratio of and/or to?

This is a ratio of the driveshaft to the axle. The drivshaft will have to turn 3.55 rounds to one round of the axle. Thus, as a rule the lower the number the slower your engine will turn at a given speed. The higher numbers give higher towing capacity since the engine winds up higher and gets into its higher torque and HP ranges easier.


As far a s towing 3000 pounds..... any of them will work fine.
As far as fuel mileage..... Look at the epa estimates for a truck with each one. IF memory serves me right the diff in the 3.55 and the 3.73 are nominal. And I think, if you get the towing package it will come with the 373. I would also suggest the limited slip as well if you will be going to off-road situations with your 4 wheelers.
Definitely get the 5.4 vs 4.6. (imho)

Keep up the homework and you will make an educated decision you can live with for many years.

 

If your buying a truck to pull, the one that pulls 10,500 is a XL regular cab 5.4L 2wd longwheel base with the heavy duty tow package and 4.10 gears. The only way you can get the heavy duty tow package and 4.10 gears is in that particular truck, but if you get a 2wd extended cab or screw with the 5.4L and 3.73 gears and 17" wheels, this is the next best truck for pulling.

The 3.55 gears will get better MPG on the highway, but if you pull with them you will strain your whole truck more to get the truck rolling(useing more gas) if you had the 3.73s.

And I agree with BigD, the towing package will come with 3.73s, and I think it comes with a LS, and if it doesn't, get it.

 

You can buy a 2wd 5.4L with the towing package and a 3.55 limited slip rearend. This is what I have with a supercab short bed. I get about 17 hwy/15 city. I don't tow that much but when I do it is usually about 5000-6000 lbs. It does pretty well but you have to turn the overdrive off in the hills to keep it from shifting too much but on flat surfaces you can leave the overdrive on. It get right at 10mpg when towing but keep in mind this is a stock trailer with a large frontal area. Pulling a utility trailer with 4 wheelers will get better because less drag.

 

To answer your 1st question...

The axle ratio is the gear reduction that is applied at the ring gear and pinion within the rear axle of the truck. 3.55 or 3.55:1 would indicate that the driveshaft is turning 3.55 times for evey single revolution of the axle/wheel. A numerically higher ratio (like the 3.73 or 4.10) gives the truck more useable torque, but this comes at the expense of running higher engine rpm for a given tire size and therefore less gas mileage when not loaded.

Axle ratios can be varried to account for larger than stock tires, increased towing performance, better "hole shots", etc.

The towing package does not come std. with 3.73's, the axle ratio is spec'ed seperately.

I have an '06 Screw 5.4L 3.55LS 4x2, factory towing, and have no complaints with it towing up to 6000#. Same with the '04 (same config) that it replaced.

3.55's will get you better mileage on the highway if you use your truck for lots of extended drives.

I agree, 3.73's are the better towing gear, but for 3000# it really doesn't matter at all.

One other thing to think about, many of the 3.73 rear ends also are on trucks sporting 18" rubber (FX4, etc.) The ratio difference isn't as great as it might appear when the rolling radius of the tire is factored in.

In short, if all you are towing will be 3000#, buy the best truck/deal and don't worry about it.

 

Sorry Big D, I missed your explaination of ratios above, thought it was a message quote......

 

No problem!

good job

 

The axle ratios refer to how many engine rpms to 1 axle rotation. In the case of a 3:55 the engine will turn 3.55 turns per 1 axle rotation. With that said lower gear ratios ( higher numbers) will allow the engine to use it's rpm band where it develops more torque. Hence the reason why the lower ratios allow you to pull heavier loads.

Also sometimes the lower ratios will have a bigger ring and pinion gear to handle heavier loads.

The difference between the 3:55 and 3:73 other than tow weight might be a slight reduction in fuel economy going to lower ratios. I have found in this truck when not towing that the 3:73 seems to be a better match, because of the trucks weight, and it keeps the engine rpms in a better part of the torque curve then the 3:55. So in this case there really is no lose of fuel economyas some have stated.

I also suggest that you opt for the limited slip version.

 

Brother you have been given alot of useful infomation aready. I got the feeling your on the right tract. I think any trim and cab with a 5.4L{if for no other reason than the upgrades} running 3:73 will serve you nicely.I had an 05 fx4 scab and my wife still has an 04 fx4 both where 5.4L geared 3:73, we never got under 15 mpg. I really think that with the 5.4L and the fx4 suspention is as close as a light superduty as you can get.

 

Don't forget... with most 4x2's running 17" rims, as opposed to the 18" rims and larger tires on many of the 4x4's, the 3.55 ratio is probably much closer to the same overall ratio as the 4x4 with the 3.73 and big rubber. In other words, the loss of torque is probably not as significant in the 4x2 model because the tire size makes up for some of it. It hasn't been that long ago that 3.73 was the granny gear and 3.08's were common...on 15" rubber.

For the load originally described, 3000#, I would get the 3.55 LS and enjoy plenty of power for towing and better mileage when you're not towing (a majority of the time).

 

Unless you get the 4x2 Lariat you get 18 inch rims are standard. You have a choice between 3:55 and 3:73.

 

Aren't 17" rims still standard on all 4x2's , unless you option them otherwise....

 

A lariat comes with 18"s.

 

first - thanks for all the information - very helpful.

based on a sticker i was sent (requested internet prices) i'm seeing a 2007, SCREW, 5.4L 4X2 with 17inch tires a 3.55 LS axle. Based on all the replies I've seen I don't think that there is any reason to hunt down a 3.73 differential, or avoid it if it's the better deal. but i think for my needs 3.55 will be the best option

now it's price / finance shopping time.
thanks.

 

The 3:73 is a better match for this truck whether towing or not.