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Old 01-05-2012, 04:11 PM
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Rear end gear question

I have a 1996 F-350 2WD quad cab long bed with 4:11 gears.

I'm getting 18 to 20 MPG depending on how, and where I drive.

I'm thinking about putting 3:55 gears in it, or taller, for better fuel mileage since I drive 60 miles a day to work and back.

I found 3 rear ends in the local junk yards with the 3:55 gears, but they where not limited slip. 2 with the code 39 one with 29. I know the limited slip will have a 3 digit code with a dash A. B. or F with the 355 gears, but in what year trucks should I be looking for for the limited slip that will work with mine without modification? I know mine has a electronic speedo.

2nd question. How much will putting the taller gears in this thing affect pulling? Keep in mind I do not pull heavy loads very often, maybe once a year for 30 miles. The rest of the time it's just a bed full of crap.

Thanks
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Old 01-05-2012, 05:13 PM
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If you need a vehicle good on gas, buy one built for it. Dont make a heavy duty truck designed for work into a baby truck.

Aside from that, your not gonna do much better than 20mpg on the highway with an auto. You MIGHT be able to hit 22-23mpg highway... but that would be the absolute highest for an auto 7.3 obs. And thats going 70mph or less.
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Old 01-05-2012, 05:36 PM
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Quote:
Originally Posted by 85_305 View Post
If you need a vehicle good on gas, buy one built for it. Dont make a heavy duty truck designed for work into a baby truck.

Aside from that, your not gonna do much better than 20mpg on the highway with an auto. You MIGHT be able to hit 22-23mpg highway... but that would be the absolute highest for an auto 7.3 obs. And thats going 70mph or less.
Your post is one example of the reasons I am doing this. I made a 5k Lb gas truck run high 11's in the 1/4 and get 16 MPG. I like doing things people say "you should not or can not do"

And I WILL get better than the mileage you posted. It will take time, but I will get it done.

So does any one have a helpful hint?
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Old 01-05-2012, 05:41 PM
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You mean a supercharged 5.4 v8 actually ran 11's?!

Ok... welcome to the 21st century. I'll post vidoes of John Deeres that will burn that f150. Hell, I'll post vidoes of tractor trailers that will burn that f150. Speed is nothing new. Making stupid things go fast is nothing new; look at all the honda guys since the 90's that try getting ****box's to go fast.
Speaking of which, I'll show you video's of 1.8liter hondas making 4-500hp that run 8second 1/4s... traction limited.

My point is, you aren't the first, you wont be the last. Trying to make a heavy duty truck into a grocery getter is just stupid. I have a diesel Volkswagen that gets 50mpg city and 63-64mpg highway, and it's smoked about 6 new 305hp v6 camaro's/mustangs, and hung-in with a 330hp/380ft-lb 2800lb M-Series 135i. Then I've got my lifted f250 for when I need to get some work done. What your doing is silly and been done before, and all the time and money and research you put into doing it, your gonna be mighty pissed when a stock whatever else rolls by and gets better mpg, holds more people, and goes faster.


355's came stock in some obs trucks, and you dont see them getting better than 22-23 EVER. How much weight you plan to pull?
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Old 01-05-2012, 05:52 PM
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Muddman I'll just say that with a lower number gear you should be able to get better fuel mileage. But you are only talking 1 to 2mpg at best. Plus with all the weight you are tyring to move, having a 3.55 rear instead of the 4.10 might actually make the motor work harder, know what I mean?
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Old 01-05-2012, 06:24 PM
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That's exactly what I'm trying to tell him. 22-23mpg is pretty much unheard of in an obs. 21-22highway is at least somewhat heard of. 1-2mpg is exactly right for 355s, but you also lose a good amount of torque, which is going ti kill you when pulling.
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Old 01-05-2012, 08:16 PM
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Quote:
Originally Posted by 85_305 View Post
You mean a supercharged 5.4 v8 actually ran 11's?!

Ok... welcome to the 21st century.

. Trying to make a heavy duty truck into a grocery getter is just stupid.


Your a real charmer there aren't you.

Opinions are like what?

I don't really care what you think is stupid. I was asking for ideas, knolage or facts, I'm not interested in what you think MY truck should be or should not be used for or done with.

But just to peek you interests. I do know where there is a truck that gets a lot better fuel mileage than you think they are capable of. I'm trying to duplicate it or surpass it, despite what you think, or your opposition. When I'm done MY truck will do exactly what I want it to do. Not what you think I should do with it.


BTW 23 MPG is not even the low end of what I'm looking for.

So again....If any one has any tips. I would appreciate it.
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Old 01-05-2012, 08:22 PM
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Quote:
Originally Posted by Lilfarmrboy View Post
Muddman I'll just say that with a lower number gear you should be able to get better fuel mileage. But you are only talking 1 to 2mpg at best. Plus with all the weight you are tyring to move, having a 3.55 rear instead of the 4.10 might actually make the motor work harder, know what I mean?
Thank you.

1 or 2 MPG increase at a time is good. The more info I can get the better off I will be, and closer to the goal I set.

As far as hauling. I rarely pull a trailer. I do put a ton or so in the bed from time to time. But for the most part. This truck is my DD and my latest experiment.
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Old 01-05-2012, 09:22 PM
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Quote:
Originally Posted by Muddman View Post
I have a 1996 F-350 2WD quad cab long bed with 4:11 gears.

I'm getting 18 to 20 MPG depending on how, and where I drive.

I'm thinking about putting 3:55 gears in it, or taller, for better fuel mileage since I drive 60 miles a day to work and back.

I found 3 rear ends in the local junk yards with the 3:55 gears, but they where not limited slip. 2 with the code 39 one with 29. I know the limited slip will have a 3 digit code with a dash A. B. or F with the 355 gears, but in what year trucks should I be looking for for the limited slip that will work with mine without modification? I know mine has a electronic speedo.

2nd question. How much will putting the taller gears in this thing affect pulling? Keep in mind I do not pull heavy loads very often, maybe once a year for 30 miles. The rest of the time it's just a bed full of crap.

Thanks
I've had both and the 3.73's. In my experience and others that I know personally going from the 4.10 to the 3.55 was gaining 2-3 mpgs on the hwy. The 3.55 will tow fine for the work you describe.
I have a good friend that went across eastern Oregon w/a RegCab powerstroke running 3.55 gears and auto and calculated over 25mpgs. He couldn't believe it and I still give him heck but he swears on it.
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Old 01-06-2012, 04:55 AM
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Quote:
Originally Posted by Muddman View Post
Your a real charmer there aren't you.

Opinions are like what?

I don't really care what you think is stupid. I was asking for ideas, knolage or facts, I'm not interested in what you think MY truck should be or should not be used for or done with.

But just to peek you interests. I do know where there is a truck that gets a lot better fuel mileage than you think they are capable of. I'm trying to duplicate it or surpass it, despite what you think, or your opposition. When I'm done MY truck will do exactly what I want it to do. Not what you think I should do with it.


BTW 23 MPG is not even the low end of what I'm looking for.

So again....If any one has any tips. I would appreciate it.
Oh, your talking about the superduty that gets around 30mpg? I'm giving you some 'knolage' and facts.. buy a car if you cant afford diesel.

My superduty with the 6spd would get 21mpg in city driving all day long with no problems. My 12v 5spd cummins could hit 25-26mpg highway.





My Volkswagen gets 50mpg city, no matter how hard I romp it.
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