Rear end change?
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Junior User
Joined: Jan 2004
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From: North Dakota
Rear end change?
I have a 1989 F150 short box extended cab 2wd pickup with a 351W, C6 transmission with an 8.80 rear end and 3.55 gears (camper special). I’m thinking of changing the rear end to try to increase the mileage. Wondering if anyone else has done this and might have any pointers?
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From: maine
To change the gears out is not to hard. You will need some good tools, and some time. You could get hole unit used out of a junk yard and put that one in. Depends on you how you feel about changing gears out.
But you probley would like to do this to save money? right? You probley get 12-15 mpg right now. You "might" get 16-20 mpg highway with some 3's or 2.73 gears. But you will probley spend 300$ or more to get to this gear ratio.
Now lets do the math. Lets say 4mpg better. 72 more miles out of a tank. save 4 gallons of gas. 8$ saved in one tank. I will take you 37 tanks of gas to make your money back.
It will take some power away. And will not tow that camper so good any more. It depends on what the truck gets used for.
But you probley would like to do this to save money? right? You probley get 12-15 mpg right now. You "might" get 16-20 mpg highway with some 3's or 2.73 gears. But you will probley spend 300$ or more to get to this gear ratio.
Now lets do the math. Lets say 4mpg better. 72 more miles out of a tank. save 4 gallons of gas. 8$ saved in one tank. I will take you 37 tanks of gas to make your money back.
It will take some power away. And will not tow that camper so good any more. It depends on what the truck gets used for.
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From: North Dakota
The pickup has become more of a car, I have a 2000 F250 PSD to pull horses with. Mostly use this rig to keep the short runs off my PSD. I do end up putting 20 to 30 miles on the pickup a day roughly. The C6 has been overhauled so I don't want to mess with it. I'm getting around 10 to 12 with it. I did put a Fram Air Hog in it which has made a difference, I haven't recheck the mileage yet though.
Last edited by fdaugher; Oct 12, 2004 at 07:51 PM. Reason: forgot
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From: USA
You could swap the whole axle for one from an F150 with 3.08 (popular) or 3.31 (not so common) gears. Another option would be to keep the 3.55 ratio and run taller tires on the truck, which does the same thing as raising (numerically lowering) the gear ratio. A truck that originally came with 29" tires and 3.55 gears would have an effective ratio of ~3.12 with 33" tires on it. Almost the same as switching to 3.08's with stock tires...
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From: North Dakota
I just put new 235/75R tires on last winter. I've been looking into new 3.08 gears for it, about $180 new. I'll start checking the junk yards next for used. What do you know about getting the speedometer back on with these changes?
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From: philly pa
Originally Posted by fdaugher
I have a 1989 F150 short box extended cab 2wd pickup with a 351W, C6 transmission with an 8.80 rear end and 3.55 gears (camper special). I’m thinking of changing the rear end to try to increase the mileage. Wondering if anyone else has done this and might have any pointers?
Where do you live around....i'm in philadelphia pa. i have 2.73's and am looking for 3.55's. we could switch if you dont live far.
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