What rear end does my F250 Have in it?
 

My '96 F250 351 4x4 with E4OD does 2,000 RPM to go 70 MPH with stock tires on it. What rear ends does it have? Is there an easy way to find out? I'd like to get a few more miles per hour with less RPMs. I know I can put taller tires on it, but the stock tires that I have are almost new, so they'll be here for awhile.

Look at the axle code on the door sticker and compare with a axle decoder chart.
Or get under and look at the tag on the axle which should have the actual ratio stamped on it.

So I looked under the truck and saw a sticker on the front axle. It says 4.10 on it, so i guess that's what it has. D-4 8 0-A was written on the sticker. The front axle is not a solid axle, it flexes in the middle.

What is the feasibility of switching the 4.10 out for a higher gear, like a 3.73?

I should explain that i don't plan on towing anything with it, I will mostly use this truck like I did my last one, for summer masonry work, which will occasionally stress the truck but not too much.

It is not going to be cost effective to switch gears. You are looking at between 500-1000 PER axle to change gears and you need to do both. Even IF you were to get 2 MPG better it would take 30,000 miles just to brake even on the gear swap cost. And that is if you get the gears changed for 500 per axle. Make it 60,000 miles if you pay a 1000 per axle(more likely)

2000rpm at 70mph with 31" tires is 3.55 gears, check the axle code on the drivers door decal, should he H5. You don't want anything higher(numerically lower) than this ratio in a truck this big, milage will get worse not better.

Do the axles themselves have to be switched out also?

You can just swap out the gears inside the differential.

IDIDiesel John- That doesn't sound that bad. I thought that maybe the whole thing had to be all taken apart. Who sells gears? I got 246k out of my last truck and this one has only 155k, so I think it might be worth it to do the gear swap. I'm going to take really good care of this truck, I even got some rust fixed at a body shop, which was a first for me... Plus, I used to turn wrenches full time years ago, so think I'm handy enough to do the swap myself.

You can find gears from a junkyard. Or the entire axle if the price is right and you wanna save abit of time.

2k rpm @ 70 with the E40D sure sounds like 3.55's to me too.
my suggestion,rather than swapping in aftermarket gears like 3.08's into a truck used for masonry,would be to just slow down to 60 mph to help improve fuel economy.not much helps fuel economy going 70 mph.too much wind resistance.

the sticker lazy k was referring to,is on the inside of the drivers door jam.there's an axle code there.not on the axle itself(however the is a tag on the axle that shows the ratio,though it's close to the bolt,and may be hard for the novice to understand it.)

If it is 3.55, I would definitely not go any higher.

The sticker says 4.10 on it pretty clear. The stock tires are p235's. the 2000 rpms at 70 mph is obviously somewhat variable depending on the terrain, as I've been driving it up and down the appalachians of western MD. Maybe I should just get a set of taller tires... I had an old crown vic police model that did 80+ mph on 2000 rpms out of almost the same engine, but I know that is comparing apples to oranges.

Umm P rated car tires on a 3/4 ton 4x4 truck? Yikes! That ain't passing a safety inspection anywhere that I know of!

Still fine of you ask me, but as long as you use that truck nothing other than to load groceries in the box.... just the empty weight of the truck alone the tires are at their maximum load capacity.

Sorry about that, its got LT235's on it. What diameter in inches is that comparable to? I put 285's on my old F250 and had to cut back the front bumper just to fit them on, but they were awesome. What percent final drive reduction would 275's get me? It might be easier to do this than to tear the rear ends apart. Plus, it would be bad a$$ to have the truck sitting even higher with more ground clearance.

A 235 should be around 9 and a quarter inches, but that can vary between manufacturers. Also, you can't figure the final drive by width, you need to post up the height ratio also, so 275/whatever.