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Old 02-02-2010, 02:48 AM   #11 (permalink)
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My 79 F150 with 4.9L 4 speed.
31X10.50X15
3.55 in gear ratio

I get 21 mpg in summer at 60 mph.

That were stock but have 4" lift kit.


Most important you need vacuum gauge and keep 15 psi or higher will help you improve mpg double.

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Old 02-02-2010, 08:35 AM   #12 (permalink)
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Quote:
Originally Posted by Jethro View Post
The 300 is a BEAST of a motor, but I've never heard of it talked about positively for gas consumption. Best of wishes! I'm guessing you have the Ford 8.8 in the rear. You might be able to find some 3.23 gears (assuming it's 3.55) to better use the MOUNTAIN of torque that motor has.
Note: You can find gears at least as low as 3.08 for the 8.8 rear ends. My father in law's truck as them(97 150, MT 4.6 4wd). I've been thinking of switching them out to 3.55's or higher for towing the race car.
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Old 02-02-2010, 08:39 AM   #13 (permalink)
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Where would I find the 3.08's? Also, would I be able to find the same axle ratio for the front tires?
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Old 02-02-2010, 08:47 AM   #14 (permalink)
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If I can't find the same set of gears for both axles, I can't change it.

I still have the gear splitter option, though.
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Old 02-02-2010, 09:04 AM   #15 (permalink)
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I don't know if they switched housings between generations but they definitely made both front and rear diffs in the 97-05? generation.(FIL's truck is a 4x4 and a 3.08). The best way to find a pair(front and rear) for cheap is to go junkyarding. On the drivers door is vehicle certification sticker, on it is an AXLE field. Here is the table you need to find a 3.08.


* 18 — 3.08, non-limited slip, F-150
* 19 — 3.55, non-limited slip, F-150, F-250
* 26 — 3.73, non-limited slip, F-150, F-250
* 27 — 3.31, non-limited slip, F-150, F-250
* 28 — 3.73, non-limited slip, F-150, F-250
* H9 — 3.55, limited slip, F-150, F-250
* B6 — 3.73, limited slip, F-150, F-250
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Old 02-02-2010, 02:54 PM   #16 (permalink)
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You, sir, are my new best friend. Ok, well, not *best* friend, but a friend none-the-less.

Any idea if the carrier for the LSD gears will fit a tighter gear ratio? I'd be amazed to find an LSD rear in the yard, but if I happened across one, I'd be hard pressed to want to pay for both when they'll let me switch and swap parts at my leisure right there on the bed of a truck. (They like me... they REALLY LIKE ME.)
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Old 02-02-2010, 06:37 PM   #17 (permalink)
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I'd guess the factory LSD will fit with the 3.08 but I honestly have no idea. I haven't actually opened up an 8.8 ford, I just did a bunch of research when I was(still am actually) looking to use his truck to to my miata to events.
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Old 02-02-2010, 06:39 PM   #18 (permalink)
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8.8 carriers are all the same. the D44 carrier break is 3.92, but it's way easier to just swap the whole differential.
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Because we are big dumb redneck Americans and we only want V8s that thunder and use lots of gas pushing our empty Super Duties down the highway at 100 MPH in the fast lane while warming our butts in heated leather seats and chowing down on double quarter pounders and texting on our cell phones. We cant understand non-V8 engines because that ain't whut NASCAR uses...
Not this American.
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Old 02-02-2010, 06:47 PM   #19 (permalink)
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Well, I definitely have some considering to do (and some diff covers to pull).
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Old 02-02-2010, 06:48 PM   #20 (permalink)
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How much will the gearing affect my speedo, if I'm going from 3.55 to 3.08? (For instance)

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