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Discussion Starter #1
I was looking at these threads about MPG and was thinking that my highway mileage seemed way less than what most are getting but I really never had a good time to measure just highway. Anyways I was wondering if somone could tell me what my rear end gear ratio was or knew where I could find out?:shrug:

I got this off the diff cover tag:

S 128 P
L55 10 2 7k24

I would really appreciate it, its just somthing I always wondered.:thanks:
 

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You need to call your Ford dealer. Just as for the parts dept. Give them the code & they'll tell you if it's a locking or nonlocking rear end along with the gear ratio. I did the same thing and come to find out I don't have a locking rear end.
 

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On the second line of numbers I'd bet if you went back and looked it'd have a 3 before the "L55" That means you have 3.55 gears and it is a limited slip.
 

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Discussion Starter #5
yep, code C9, 3.55 limited slip :thanks:
 

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you have the good gears for mileage 3.55 the question is how do you drive and how fast to you cruise down the highway.

With my truck on 4.10s I pull 15-16 @ 70 but pull 18-19 if I'm down to 60-65

Oh and if your 4WD then it'll hurt your mileage some too.
 

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BJS said:
you have the good gears for mileage 3.55 the question is how do you drive and how fast to you cruise down the highway.

I'm not so sure about that. I know I've seen some guys that get really good mileage with the 4.10s. Better than I've ever gotten with my 3.55s. And I've heard guys towing getting better mileage with the 4.10 gears too. When I first got my truck I wanted 4.10 gears but not that it makes a little bit of power there is no way I'd want to go to 4.10s.
 

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Discussion Starter #9
yea, I would of thought it would be better for highway too but it seems my milage is better around town.:shrug: I'll get some good highway results since were going wheelin next weekend and its a good 1.5hr hwy drive at around 55-60. Only Thing I can think is on the interstate its easy to eat up every bit of 70-80 to keep up with traffic. At that speed im holding around 2k rpms and it keeps a steady 7psi of boost. Could it be that the 4.10s make it easier to pull the weight of the truck so its not lugging it so much:shrug:
 
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