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Old 01-02-2009, 07:04 PM   #1 (permalink)
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Diesel Gear Ratios

I had this thought from another recent post. I often borrow my brothers F-350 Diesel. It is a 2006 and has the 6.0L in it. The current gear ratio is 3.73 as it is 4x4 and has a tow package.

He does tow a heavy trailer and a swamp buggy at least once a month. He claims horrible mileage, but I know alot is driving habits, I am working on correcting that problem.

My question is; What gears can he come down to and still be able to tow near 8000 pounds? I'm sure he will benefit from a gear swap if possible.

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Old 01-02-2009, 07:27 PM   #2 (permalink)
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He could probably drop down to 3.55s, but when you tow heavy (esp if it is up and down hills) even diesels can get pretty bad fuel economy.
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Old 01-02-2009, 09:43 PM   #3 (permalink)
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You could easily end up with WORSE fe if geared too high. It will want to drop to a lower gear all the time.
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Old 01-02-2009, 10:22 PM   #4 (permalink)
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I use 3.08 gears. I have no problem towing 10,000 lb trailers, sometimes through hilly country. These things have staggering torque as low as 800 RPM.

If he is a 4x4, the numerically lowest gears he can get for his front axle is 3.55 and the improvement is not worth the trouble. For 4x4s an overdrive works better. It would give you an overall 2.98:1 ratio. Overdrives are pricey, though. I could not make one make sense and I drive 25,000 miles a year.

A ratio lower than 3.55 could be trouble for an automatic transmission.

Ford now offers a 3.55 ratio as standard on diesel pickups.
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Old 01-03-2009, 08:57 AM   #5 (permalink)
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Quote:
Originally Posted by Big Dave View Post
I use 3.08 gears. I have no problem towing 10,000 lb trailers, sometimes through hilly country. These things have staggering torque as low as 800 RPM.

If he is a 4x4, the numerically lowest gears he can get for his front axle is 3.55 and the improvement is not worth the trouble. For 4x4s an overdrive works better. It would give you an overall 2.98:1 ratio. Overdrives are pricey, though. I could not make one make sense and I drive 25,000 miles a year.

A ratio lower than 3.55 could be trouble for an automatic transmission.

Ford now offers a 3.55 ratio as standard on diesel pickups.
That is correct, they do offer a 3.55, which I may recommend he switch to. He does not however use the 4wd often and the truck does have and O/D. He and I both know MPG's tank when towing, but he wanted to improve his numbers on the street, empty. I had proven to him previously that the truck is capable of at least 22mpg, maybe now he'll change his habits. I just figured I would research all options to help him with this beast.
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Old 01-08-2009, 02:46 PM   #6 (permalink)
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I just yesterday sold a 97 Dodge 2500 with a Cummins diesel. When I bought it the truck had 4.10's and I couldn't get more than 17 mpg on the highway. I swapped in 3.55's in an effort to increase mpg and it really didn't make much of a difference - and may have actually hurt mpg in the city. I did get nearly 19 once - but for the cost of the swap it probably wasn't worth it in hindsight. Oh well - not my problem anymore!
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Old 01-08-2009, 03:41 PM   #7 (permalink)
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I would suggest the addition of a scangauge to help adjust the "nut behind the wheel". There is nothing like realtime feedback to alter behavior patterns.

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