F-350 final drive options?

When I got my 97 F250 HD with the desiel, the options were 355, 373, and 410. I went with the 355 and it was a mistake. I would either stick with the 410 or maybe get a 373.

With the 355, I had to be above 80 for it to run decently. Loaded, below 80 it would lose speed when on cruise control and going up hills. Above 80 (even *way* above 80) it would maintain speed on cruise going up almost anything.

Throwing a whole bunch of gearing at it might not make as much difference with the mileage as you think. I had friends with 410 rears that got better mileage than my 355! (They also drove a little slower, too)

You bought an F-350. Is it a diesel? That thing weighs more than 3 tons, I wouldn't expect very good mileage. If something is wrong with it and you are getting worse mileage than others with the same vehicle than that's what I would fix first. Maybe you should ask what other people have been getting to see if the truck is average.

For gearing if I was worried about mpg I would go with a reasonable gear set, say 3.73. If I was being realistic and realized that I want to put bigger tires on the 4x4 then I would go with the 4.10s.

The cost of regearing or a new axle would probably be lower than the cost for that overdrive unit. Is it a 2wd?

Lots of questions, but I think with the non powerstroke you won't have enough power for tall gearing.

What size tires are you running? The cheapest way to cut the cruise RPM will be to install larger tires. The add on box your referring to is either a Gear Vendors or US Gear unit - $2500 plus installation. Regearing will probably run ~$750 per axle if you have a shop do the work.

Brian

You may want to consider switching to synthetic lubricants.
Not just engine oil, but also tranny and the diff. as well.
Wont do miracles, but it has helped in our shop trucks.
(99 250 SD 5.4V8, 00 250 PS SD, & 01 250 sd V10.)

Not to bum you out though, but i wouldnt expect to get very decent milage out of a truck like that (unless it's a PS), that's not what they're built for.
(i realize that every little bit helps though.) :thumb:

At the last place i worked at we used a F-SuperDuty dually crew cab (460 gas auto.) :scream: to tow a 40' fifth wheel to automotive swapmeets on the east coast. That truck got about 4 to 5 mpg.......weather it was towing the trailer or not. :scream: :scream:

Are you sure you have 4.10s? 2300 rpm at 75mph sounds low for 4.10s and stock height tires. I have 4.10s w/~35" tires and I'm turning 2300 rpm at 75mph. 2000 rpm is 66 mph per my GPS. If you really want to improve you MPG you need to slow down - the wind resistance at 75mph is killing you. I lose 2mpg by increasing my cruise speed from 65mph to 75mph.

Brian

The ford diesel is VERY sensitive to rpm in regard to fuel economy. You have the advantage of a smaller and better aftermarket turbo (the stocker is too big...silly ford guys :confused: ). The milage sweet spot is 1800 rpm to about 2100 rpm on a stock engine it is usally wider with an aftermarket turbo. Above 2100 rpm milage will drop off quickly.

To be honest 16.5 m.p.g. is very good and it not going to get much better.

In cold weather mobil 1 gear oil will also help milage, as I recall your unit did not have sythetic oil in from the factory. Any Ford truck that had an axel filled with sythetic oil will say so on the axel tags held in place by the bolts that hold on the diff cover. Be advised there are oils out there (castrol syntec) that claim to be sythetic and are not :eek: , mobil 1 is the real thing and so is amsoil.

Is you F350 a dual rear wheel or a single. The dual is a dana 60 axel and the single is a visteon. The axels on these trucks do overheat when towing and the input shaft seals start to leak once they have been overheated, axel failure rates on these trucks that tow are very high. For the dana axel (drw) get the Ford diff cover from a F450 and put it on it is by far the best cooling cover out there. For the F250 and F350 srw guys (Visteon axel) get an Ultraduty.com diff cover, it is the same as the f450 cover made to fit the Visteon axel.

Hey, if you do end up wanting to change the gearing, its pretty easy to find ones people have pulled. I put 4.56 in to replace my 3.73 or 3.88, i forget. But anyways, my old ones are in perfect shape (18k mi)and I know of several people that have changed theirs out and just have the gears laying around. But actually Id love to get 16mpg. I usually get anywhere from 6 to 10 mph. Good thing its got a 40gallon tank!