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Joined: Jun 2017
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I have a 85 f250 diesel (6.9L) dually. It has a 3 speed auto. I'm planning on switching out the 4:11 axle ratio. But also need to know what tranny i can put in (that will bolt directly in) to raise my fuel economy and drop my rpm's. Any help or suggestions will be greatly appreciated
Cargo Master
Joined: Oct 2005
Posts: 2,295
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From: NJ
ZF5 is the way to go. With 3.55:1 gears going from C6 to ZF5 my MPG unloaded went from 12 to 15 mostly around town and towing 10.5 to 13.5. Unsure of straight highway MPG unloaded, I'd have to check my records for the C6 and I haven't measured that yet with the ZF5. From what I've seen though it seems to be a solid 3 MPG increase all around, in a 6600 lbs 4x4 crew cab.
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Lukes66
Pre-Power Stroke Diesel (7.3L IDI & 6.9L)
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Jun 28, 2011 04:00 PM
