jacobs4x4

I hear everyone talking about gears and I've never rely thought about it much. But now I am. Some of you say it could increase MPG? My truck is a 97' F250 LD 5.4 V8 4X4, I've got 35" mud tires, I dont drive highway much average speed I would say is around 35mph, some times I pull a 3500lb john deere around town. I'm pretty sure I have the 3.55 now. I've seen some of you say to go with the 4.56 for 37's I think. What would you say for mine with 35's. I found some for like $189.

Will that affect my 4X4? I know the usual dont put it in unless I'm on dirt or something. Is that all or is there more.

My main Q's are

Am I right about the gears I already have.
What gears should I get for what I have/do
Does it help MPG
Is it worth the money

Good old Bill

Obviously, you can't run different gears in different axles, you have to change both. If the truck is doing the work, let it be. Any B/S about extra mileage or power is just B/S. You will NEVER, recoup the expense.

MIRMAN

Really it depends on what rpm's u r turning with your current gears. say at 55 mph a stock vehicle usually is somewhere around 1600 to 1800 and i beat your only around 1400 and it kicks in out of overdrive alot on you. i only say this b/c i had the same problem and i chose to put 4.30 in and it did help my mpg's b/c i wasn't lugggn it to death.

jacobs4x4

Mine is independant suspension I know what you mean tho but is rely a big deal as long as I only use it in the mud

Im not sure about 55 but I'll see today. I do know at 65 im at about 20-2100 so I'm probably running about 17-1800 at 55.

I know I should'nt have done it but last night I did 110 at 4000 rpm's

driver444

I'm almost positive that the only gearing you could get in that truck from the factory was 3.73 or 4.10, being a heavy duty. And if it's a short box, my money's on the 3.73. Also, from the RPM you posted I would guess 3.73. You can look on the metal tag on your rear-end cover and it will tell you.

That's a decent all-around gear for you I think. 4.10 would be better for that size tire for power reasons, but if you're only towing 3500#, (not even close to your rating), as the last post said, Not worth changing. The 4.10 gears would basically put you at the factory tow rating, at factory RPM's except with the 35 inch tires. Increasing tires size effectively raises your gear ratio.

Yes, the gear sets are usually only around $200, but the labor is a killer, (especially on the front end) and gear swaps really do need to be done by a pro. Pro=Expensive.

As far as different ratios in the front and rear end, not only would you grenade something (usually a transfer case) if you ran it on the road like that, but in mud and dirt, they would be fighting against eachother. Your front tires would be turning faster than the rears, and not being able to go anywhere, because the rears would be slowing you down. AND, if you "shift on the fly," you'll in effect be shifting with your front and rear axles traveling at different speeds, and we all know what that does. You'd litterally have to stop to shift to 4wd. Just a bad idea from the get-go.

jacobs4x4

To find out what gears I have what should I look for. I saw a list on here a while back but searched a little and could not find it again.

driver444

There is a small metal tag attached to one of the bolts holding your rear differential cover on. It will have your gear ratio stamped on it. It will say for example...

3 L 37 for 3.73 limited slip
4 L 10 for 4.10 limited slip
3 73 for 3.73 regular axle
4 10 for 4.10 regular axle
Or you could look at the "axle code" on your door jamb sticker. It'll be a 2 digit code like "C5" or "H5". I don't know the codes, but the dealer could tell you what it is. Somebody on this site's gotta know them.

flareside93

4.10s are the biggest you can go in your current axle.
they offer good acceleration off the line when you need it, providing your tires can grip it.
they are good for the low end applications, and wont let you down at highway speeds.

someone who knows more than i do correct me if im wrong.

driver444

I agree that 4.10's are probably ideal for a truck with 35's. I'm not sure that it's as low as he can go though. If that's F250LD, I believe it's a 10.25" axle. Not a 9.75" like most of the rest of us with 5.4 engines. If that's the case, he could use 4.10, 4.30, 4.56, and maybe even 4.88.

Again, I could be wrong, But if it's a 10.25" axle, It's the same that's in my 1996 F350, and all of those gear choices were available to me. But I stand with what I said before.... "leave the truck the way it is if you're happy with the power, and driveability."

willys5555

why do yall say 4.10s are the biggest he can get? i have the 8.8 and did research and i could put 4.88s in it. but i decided to get the 9.75 axle and am going to put 4.88s in that one instead...maybe i mis-read or am just confused but i know you can fit 4.88s in both the 8.8 and 9.75