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Old 08-22-2007, 06:56 AM
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rearend ratio

I have a cc dually psd. with a 5 speed. 2wd. i have 4.10 gears with a 235/85-16 tire. they are 1 inch taller than the 215/85-16 that came on it. 235 is stock for 250's obs and duallys 99 and up. i was wondering if anyone has gone from 4.10 to 3.54 gears and if it helped or hurt milage. I am looking to get a little more mileage. i am turning 2900 at 75. i drive about 350 miles a week. I also do not pull a lot. mostly bob tale is how i run. so i know why do i have a big truck. well i am 6'4'' tall 250 lbs. i dont belong in anything else. thanks for your help in advance.
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Old 08-22-2007, 07:29 AM
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I would not go to a 3.55:1 but I would go to 3.73:1 gear ratio. It will drop your rpms to 2,000 at 75 mph.

I don't know what mpg you will get but I know my 2002 F-250 crewcab 4x4 with 3.73:1 gear ratio averages 500miles per tank.
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Old 08-22-2007, 07:48 AM
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I have been told that the expense to change differential gears is not worth the increased mileage. Maybe a better solution for you is double overdrive from a company called gear vendors. I am gonna get their setup eventually. THis would be a great setup for someone that does little towing but alot of highway miles. check them out. Gear Vendors Under/Overdrive Ford 2-Wheel Drive Manual Transmissions.


Hope this helps.

Rob
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Old 08-22-2007, 07:52 AM
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Quote:
Originally Posted by rajharley View Post
I have been told that the expense to change differential gears is not worth the increased mileage. Maybe a better solution for you is double overdrive from a company called gear vendors. I am gonna get their setup eventually. THis would be a great setup for someone that does little towing but alot of highway miles. check them out. Gear Vendors Under/Overdrive Ford 2-Wheel Drive Manual Transmissions.


Hope this helps.

Rob

In a 4wd as yours Rob I would aggree with you. But in a 2wd the cost of changing gears is worth the extra fuel mileage. I just think going to a 3.54:1 or 3.55:1 is to low. I think for performance issues going to a 3.73:1 is better option. Also the 3.73:1 can be found at most junkyards. You can swap out the whole rearend. You maybe even able to trade your rearend with the 4.10:1 gear ratio for part of the cost if you go to the right junkyard. Then you just have to swap out the whole rear axle saving you money and time.
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Old 08-22-2007, 07:58 AM
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I agree that the 3.73 is a better choice if you are determined to change. But it doesn't sound like you drive enough miles to recoup the expense. If you drove more miles per week or if gas prices went up considerably from the current $3/gallon then it would be worth it.

I have a 4.10 and I drive 170 miles per day. I turn 2k rpm at 60mpg and I get 18mpg. If I'm really feathering it I get 21mpg. This is with the stock software.
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Old 08-22-2007, 08:03 AM
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Jacksd3, your comparing your 03 6.0L to an OBS 7.3L. from the dealer being completely stock you get better mpg then the OBS 7.3L. I think the OBS gets around 14-16mpg at best. So swapping out the rear end in his situation would be a good idea. Again that is when you go talk to a junkyard. See what they will do on the cost if you trade out your rear end with 4.10:1 gear ratio with one they have that is 3.73:1 gear ratio. Being the 3.73:1 was a gear ratio used in these the junk yard may have a stock one on hand.
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Old 08-22-2007, 08:20 AM
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Hi bigcountrysg, I agree with your last comments. Should be easy to find a 3.73 at most of the dismantlers.
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Old 08-22-2007, 08:38 AM
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BC I see your point there. And wouldn't a junkyard rather have a 4.10 on hand for the guy that might want one for a hotrod?
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Old 08-22-2007, 03:41 PM
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THAT'S A BIG 10-4 ON THE GEAR VENDORS.......

Quote:
Originally Posted by rajharley View Post
I have been told that the expense to change differential gears is not worth the increased mileage. Maybe a better solution for you is double overdrive from a company called gear vendors. I am gonna get their setup eventually. THis would be a great setup for someone that does little towing but alot of highway miles. check them out. Gear Vendors Under/Overdrive Ford 2-Wheel Drive Manual Transmissions.


Hope this helps.

Rob
Couldn't agree with you more, Rob, on the Gear Vendors! I'm about to do one of those myself.........sounds like it might be just what the doctor ordered for the original poster.

Jerry
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Old 08-22-2007, 04:12 PM
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If it were me I would go to a 3.54 as you stated. Thats what the OBS came with or 4.10's. I believe the 7.3 has enough torque way down low to be able to run the 3.54's. Since you have a 2WD it would be cheaper to change the gears than have a gear vendors installed. If you do pull a load it will take a little longer to get up to speed but since you don't pull that often it would more beneficial to go with the higher (numerically lower) gear ratio.
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