Has anyone here ever done this of considered this as it seems like these f550's could be enhanced towards efficiency. The GVWR is 17,500 on my 2000 f550 and have seen many f450's pulling comparable weight. just a thought as there is a wealth of wisdom on here, thanks, Ron

 

Do you mean Gross Combined WR or do you mean you can put about 8000 on the truck itself, or tow rating?
Joe

 

Most F-450 chassis cabs have the same axle ratio as the F-550 trucks for the same given engine type. If you need better fuel economy then you need a smaller truck. Fuel economy is way down the list of concerns for anyone who needs an F-550 truck.

 

been driving the big rigs for years and well aware they only get 8 mpg so there should be a way for these f450's and f550's to get in the teens loaded. The mind set of 8mpg being acceptable was okay in the industrial age then diesel was less than a $1 a gallon. somethin seems fishy here. Pullina set of doubles empty or loaded we always got between 7.5 and 8 mpg

 

What fuel mileage are you getting? I know people with dump bodies that get double digit fuel mileage with the 2000+ 7.3l powerstock diesel loaded. They have manual transmissions.

Your big rig engines is probably close to twice the displacement of these engines with two less cylinders. Bore and stroke are completely different as well as the number of gears. Big difference in performance between the two also, especially acceleration.

 

getting 11 and 12 mpg with the slushbox, did a few things like ebpv delete and 6637 intake , so am basically interested to learn of the best mpg's attained with these trucks. sure it depends on hauling , and empty miles, and a few other variables and certainly seems that the zf6 models are more efficient.

 

If you are already getting 11 or 12 with your 2000 F-550, gas or diesel, then you are doing great.

If the goal is saving money, the costs of swapping in an F-450 axle of the same year make take a while to recoup. And unless you downgrade to a taller rear ratio, there will likely not be any gains at all.

Plus, since the drop in third member of the 550 axle extends further forward, and since the U joint yoke size is different, you will need a new driveshaft, as it will have to be longer to reach the 450 axle, with a smaller yoke.

And, since the 450 axle is round tube, and the 550 axle is square tube (for 99-04 models with 8 lug (not 10 lug) 19.5 wheels on 225mm bolt circle diameter), you will not only need new U bolts, which is a standard practice anyway, you will also need new spring seats and caps, because the new U bolts will need to be mounted upside down for the round tube axle.

And, you may need new brake lines, and possibly a new emergency brake cable, because the F550 brake calipers are mounted forward of the rotors, while some F450 brake calipers are mounted rearward of the rotors, and that will effect the entrance direction and length of the brake lines. There was some variation of brake caliper orientation during those years, so that issue may be axle dependent.

You mentioned the fuel economy of the big semi's. And a responder pointed out that the semi's have 10, 13, and 18 speed transmissions. They also have a narrow rpm band, that typically doesn't exceed much more than 2000 RPM. The real power is between 1200 and 1800 rpm. By contrast, an F550 as well as an F450 with 4.88 gears will have to cruise at 2500 RPM to keep up with traffic on the highway. If you have a V10 with a 5.38 ratio, then your RPMS are all the more higher. Down grading the gear ratio will have much more of an impact over downgrading the axle hardware.

You can downgrade your GVWR capacity by going to a taller rear ratio in the same axle that you already have. The ring and pinion may not be available from Ford, but it is available from Dana. You can get ratios for the Dana S135 as tall as 2.81

Here is a list of available ratios taller than what you may currently have, along with the Dana Part number to the matched ring and pinion gear set:

2.81 360KG114-X
2.92 360KG115-X
3.07 360KG100-X
3.21 360KG102-X
3.38 360KG103-X
3.54 360KG104-X
3.73 360KG105-X
3.91 360KG106-X
4.10 360KG107-X
4.44 360KG108-X
4.78 360KG109-X
4.88 360KG116-X
5.13 360KG117-X
5.38 360KG120-X

These ring gears are 14.2" in diameter (larger than the current F550), so they won't be cheap. You'll also need a new differential case flange half and cap half with all the bolts, because if you change ratios beyond one or two steps, a new differential case (not axle housing) is required.

Here's the part numbers to the new case kit you'll need, that depend on the ratio you choose:

2.81 thru 3.21 360KQ100-X
3.38 thru 3.73 360KQ101-X
3.91 thru 4.44 360KQ102-X
4.78 thru 5.38 360KQ103-X

You may also need a bearing and seal kit, especially the seals: 360KS100-X

And the bearing and cup for the Inner Pinion Kit is: 360KS102-X

And the bearing preload spacers... you can get a kit that has about seven thicknesses of shims that range from .300 to .306 in increments of .001: 360KV100-X

One caveat to keep in mind that changing the ratio to a taller gear can sometimes WORSEN fuel economy, depending on terrain and loads. The taller gear may end up keeping the transmission in 3rd gear more often just to pull a slight grade, which may increases average cruising rpms higher than what they with shorter ratio that allowed the transmission the use of its fourth gear. With one less gear to maximize the use of the engine's power band, there may not be any savings at all.

Flat lands and lightly loaded, there may be some small gain. A big gain will by how much quieter the motor is cruising at 2000 rpm versus 2500.

Hope these part numbers help you. I had to hand type them from paper notes, as I have not found them anywhere online. I made some mistakes that I already caught and corrected. These parts are circa 2000, so they are built for your model year axle, but they are not Ford part numbers, they are Dana's.

 

had to reread this info as Im considering a purchase of a 2001 f450 4x4 5 speed and it has a bolt snapped off in the carrier. Fortunately since the last time i posted on this topic i bought a 2004 f550 parts truck and saved all the axle springs so it would be a direct bolt on. Currently researching if the carrier u bolts snapping are a common concern in the f450 axle.

 

look into a compress natural gas add on kit. it basically augments what you have now and provide fuel savings and more power.

its about a $2000 upgrade. if you run a lot of miles, the payoff on return on investment could be practable.

 

$2000 for everything?

When I looked into this years ago, the cost wasn't in the kit per se, it was in the tanks.

By the time the costs of new tanks... used not permitted, and most CNG tanks have a 20 year maximum rated life before being pulled from service, and even then, they still must be inspected every 3 years... that are DOT certified, 3,600 PSI rated, sufficient enough GGE size to last between high pressure filling stations that are few and far between, equipped with the pressure relief device, one way valve, electronic shut off, strapped and shielded... we were in the $12,000 to $15,000 range out the door.

The lions share of this cost was in the tanks (fully compliant tanks that is). If in an accident, I would not have the resources to personally shoulder the liability of negligence that would not be covered by insurance from not being compliant.

Now prices and supply may have changed in the nine years time since I last looked into this, but $2,000 still sounds like some cost factors are missing in that estimate.