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  #1  
Old 09-29-2011, 08:12 PM
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Switching To 3:55 Gears

I'm currently running 4:10s and it's really a waste because it's more of a daily driver than a hauler. I bought the truck to tow my show truck to shows and that only happens a few times a year. If I was to re gear to a 3:55 would I see a little better gas milage and quieter engine on the freeway? Also is the task something I could do at home solo? Any help is appreciated. Also any links on where to purchase the gears?
1996 F250
7.3
4x4
5 speed manual
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Old 09-30-2011, 06:06 PM
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iom heard of some people doing that. and yes it would bring down the rpms.

mine has 4.10's as well and at 70 mph its almost 2500 rpm! but don't think that it would be worth the investment but thats just my opinion. i've found both the front and rear diffs here local for $900 for both. plus then your looking at a good days worth of labor..
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Old 10-03-2011, 03:57 PM
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I have a 97 f250 ( 4 inch exhaust, 10k mod, napa filter , FPR shim) with f350 suspention, dana 60 front, heavy rear leafs ect. I have 3.55 and a zf5 and im turning just under 2200 @ 75, about ~1400 @ 50. I have owned the truck for ~ 4 tanks of gas so far @ these are my reported gas mileage


1- 21.9 MPG ( drive home mostly back road @ 60mph speed limit, some hills)

2-17.5 MPG Around town ( just got the truck and was messing around, revving it up much more then I really needed to unloaded...the turbo is fun)

3- 18.6 (Driving mostly to work and back...once again back roads were the speed limit is 50mph, and its not flat, hills ect)

4 - 19.9 ( Driving to work more, with a solid 50ish miles of highway ( went to help my friend get things out of his truck he crashed)

-----Each fillup is approx after 200 miles and I fill at same gas pump until it click off. I have had no reason to drive highway so I do not have any idea what I would get, i'm assuming a solid 23 honestly.

-----My driving style is very laid back, I realize the truck will not be fast, so why push it and throw my mileage down the drain? I start off in second most of the time, and shift into third before applying much throttle, i then accelerate and shift at 1400ish rpm's unless im going up a hill or trying to accelerate.


I do not lug the engine( I like to be ~ 1300-1500 rpm when driving), I feel , if i'm lugging the engine and have 1/2 throttle i feel im buring more then if im at 1500 rpm at 1/4 throttle ( is this correct?)

take it easy, breath.. these engines will sip the fuel ( i would say i also leave my truck idling approx 1-2 hours per tank. Anything under 5 mins I wouldn't dream of shutting her down. Anything over 20, I think about it....and i really hate when somthing is supposed to take 10 mins' then an hour later i walk out and shut the truck off -_-

Thanks!
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Old 10-05-2011, 02:04 PM
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csdwarf11,
Thanks for all the info bud. I'm switching my gears (3.55) at the end of October and I'll be sure to post the changes as well. That 21.9 MPG sounds sweeet! Unfortunately I live in Houston and driving 60 mph on Interstate 45 is not gonna happen. I might get ran over by a hybrid going that slow...haha. I like to keep the truck running on short stops also. Just last week I had an alarm installed with the option of taking the remote with me and leaving the truck turned on. Works great for store/grocery stops. BTW how hard was that D60 swap on youf F250. Does it all bolt right up? What about brake lines etc?
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Old 10-05-2011, 06:07 PM
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I bought the truck with the D60 installed, the guy who did it did a very good job, and as far as I can tell it pretty much bolted up, he used the entire front and rear end of the f350 springs and all, and the brake lines are new, and he made them himself (flange tool, fittings ect).


Sorry i cant help with information of that, but If you would like i can snap some good pictures sometime, any specific things you want pictures of?

________________________

Were i live its all small highways, big hills ect. I finding I can get a solid 19MPG.

I like to run at 60mph because that is were I seem to just start to come onto boost and i can stay off the turbo. The truck has no problem going much faster, just cant give any honest MPG figures at highway speeds 75mph or whatever, but i bet its pretty decent.

The truck will pull 60-80 quickly, and ive had her doing 100 but anything past that I dont know




Sorry i cant be more help!!!!

Last edited by csdwarf11; 10-05-2011 at 06:12 PM.
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Old 10-06-2011, 09:07 AM
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I have 4.10's also, and if I drive 75 (very seldom) I feel like the truck is going to explode at any minute. If I had a 2wd, I would have swapped out the rear end by now to 3.55's. I still get 19mpg on the highway, but I run 60. and like OP said, running 60 you about get run over. I drive 60 from Dallas all the way to Iowa twice a month. I would love to run 70-75, but that would increase my fuel cost from 350-450 on a single trip. And yes I sometimes think I'll swap out the rear end and just take the front drive shaft off, but then I come to my senses and realize that is retarded. LOL

I would think just buying a new ring and pinion would be way cheaper than trying to swap in a whole new axle. You just need to be able to shim it and get everything lined up correctly.

Curious as to any thoughts anyone might have
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Old 10-08-2011, 11:58 AM
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I would go crazy driving 60 mph to Iowa! I have pretty much convinced myself about the swap especially if it's going to my dialy driver now. 19 mpg I hope to be in that range once the swap is done as well.
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Old 10-08-2011, 02:08 PM
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I just made the trip last night, and drove 65. Living on the edge!! HAHA! Still got 18 though. I bet once you swap to 3.55's it will get you into the low 20's. The 7.3's love to run about 1800-1900 RPM. At least that is mine's sweet spot.
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Old 10-10-2011, 03:43 PM
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I have 4.10's too, get about 17-18mpg driving 60, my wife and i took it to galveston for our cruise and driving 70 the whole way I only got 16. I thought about 3.55's but I plan on 36-37" tires so I'm gonna stick with the 4.10's
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Old 10-13-2011, 11:49 AM
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Tires would be a much cooler looking way to lower RPM's on the highway. Good thinking!!
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