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Old 04-05-2012, 07:11 PM
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Diff Gearing

Thinking about getting a '99 F250 but am thinking about increasing the ratios in the diffs to something that will extend mileage a little more. Not planning on doing a whole lot of towing, but will be off-roading for hunting...nothing "dedicated." Does anyone know if a lower ratio than 3.55 is out there for the diffs in this year range and who might make them?
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Old 04-05-2012, 07:34 PM
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Hum, I think you have either a 10.25 or 10.5 sterling. Same basic diff, different pinion gear shaft length and bearings, and sometimes 3 pinions versus 2. But anyhow, ratios go up to 1:3.08 I believe. I say up, because I think you are wanting to re-gear "up" in ratio to a lower number. If I'm wrong, the other end of the spread is 1:4.56 or maybe 4.88
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Old 04-05-2012, 08:27 PM
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OBS had a 10.25, SD's have 10.5.
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Old 04-06-2012, 08:55 AM
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Thanks. Was trying to find out through VINs or the DANA website. This narrows it down a bunch.
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Old 04-07-2012, 07:51 PM
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3.08 would make it a dog. Something in the 3.3-3.4 range with 30-31" tires (narrow 32's would be ok with 3.4) makes a good combo for weight and RPM.

Gets me 24mpg in a ex cab 4x4 6.5 chevy. I have 3.08's and 29" tires on my 82 6.2 (non turbo) and it sucks for speed but will crusie like no other.
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Old 07-20-2012, 03:27 AM
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look into the 3.31 gear swap. The newer trucks use them alot. I'm looking to swap these into my cummins 6spd manual excursion etc.. currently i have 4.10.. the 6 spd makes the rpm pretty high etc. Only issue is cost I heard the ford dealer is only place to get the new 3.31 gears.. and they may be costly...
Thanks,
deo
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Old 07-20-2012, 04:24 AM
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My automatic OBS has 410's and it has tons of power and great cruising rpms. Granted, I'm on 35's. My 6spd super duty, dont remember gears, would rip a house off of its foundation though.
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Old 07-20-2012, 12:06 PM
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Quote:
Originally Posted by Therabbittree View Post
look into the 3.31 gear swap. The newer trucks use them alot. I'm looking to swap these into my cummins 6spd manual excursion etc.. currently i have 4.10.. the 6 spd makes the rpm pretty high etc. Only issue is cost I heard the ford dealer is only place to get the new 3.31 gears.. and they may be costly...
Thanks,
deo
Those new trucks have a five speed tranny and towing package for the tranny. That's how they can get away with the low ratio and still be usable.

Sent from my EVO using AutoGuide.Com Free App
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