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Old 03-22-2010, 10:43 AM
blawknox977 blawknox977 is offline
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will changing my rear axle gears improve MPG and power?

hi im new! just bought a 99 F250 SD 5.4L with 60,000 on it. my truck seems very dogish and not much pep i know its not the greatest motor in the world but i would like to beef it up. i was wondering what gears to use that are all around improvement including MPG???

thanks Caleb
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  #2  
Old 03-22-2010, 10:46 AM
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Start with a SCT X3 tuner with custom tunes from 5 Star Tuning. More appropriate gears would be the next recommendation.


Got a 5.4L V8 Ford F150-F250-F350-E Series Van?

5 Star Tuning
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  #3  
Old 03-22-2010, 11:01 AM
blawknox977 blawknox977 is offline
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thanks! now the truck was sitting for a while thats why so low miles, the owner was in and out of jail... a lot...lol you think anything else like injectors or something need to be cleaned or replaced to restore power?
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  #4  
Old 03-22-2010, 11:26 AM
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Change out the fuel filter if you haven't already.
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Old 03-22-2010, 11:31 AM
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I would replace and/or change the following:

Fuel Filter
Air Filter
PVC Valve
Spark Plugs
Test COP's & Replace If Required
Test Battery & Replace If Required
Sepentine Belt
Change Oil & Filter
Change Coolant
Change ATF and Filter
Examine Ball Joints
Examine Brake Pads
Lubricate All Zerks
Get Safety Inspection

Hey, you asked... LOL!
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  #6  
Old 03-22-2010, 11:56 AM
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Quote:
Originally Posted by blawknox977 View Post
hi im new! just bought a 99 F250 SD 5.4L with 60,000 on it. my truck seems very dogish and not much pep i know its not the greatest motor in the world but i would like to beef it up. i was wondering what gears to use that are all around improvement including MPG?
Changing the ring and pinion ratio will not make your engine produce any more power, but it will put the engine power where you can make better use of it.

Gearing is a quirky subject- you find a lot of answers and opinions, and many of them are 180* opposite from one another. With that said, I am all for changing out ring and pinion gears for lower (numerically higher) ratios... especially if a truck has larger than factory sized tires.

Also, I have never seen lower gears dramatically affect fuel mileage. (I'm using I statements here) Tires make a bigger difference in fuel mileage than gearing because an engine's RPM is not the only factor in how much fuel is used. Load (engine vacuum) makes an even bigger difference in fuel mileage than tires do. In most cases where bigger tires are concerned, changing the original ring and pinion ratio actually increased fuel mileage, increased how "peppy" the truck feels, and generally made driving that much more enjoyable.




There are some facts we need to get straight here before you spend a bunch of cash on new gears and the proper installation.

First, you have a '99 model Super Duty with a 5.4L. That means you have one of the weakest inceptions of that engine. Someone will have to help me with the specifics, but your engine was rated for about 260hp from the factory. If I were to re-gear, that fact alone might tempt me to go one step lower in ratios (4.10 to 4.56... 4.56 to 4.88)

Second, which transmission do you have, the auto or the manual? Some people maintain that automatic transmissions can get away with a slightly higher (numerically lower) ratio. The torque converter helps mask gearing disadvantages when taking off from a stop by multiplying engine torque whereas the clutch in a manual has to, perhaps, slip a little more to get a bigger tire rolling or a heavy load moving.

Third, we need to know what tire size and axle ratio your truck currently has in it. If you have factory tires that are 31-32" tall and the 4.10 axle ratio, your about as good as you can get gearing wise. The tuner mentioned earlier will give your 5.4L a few more hp and firm up the shifts in an automatic transmission, but at that point it is what it is. On the other hand, if you're trying to push around 35" tires with 3.73 gears, I'd think real hard about changing out the ring and pinion. The tuner will help in that situation, but it can't correct inadequate gearing.

Lastly, take all the above info and factor in your driving style. A heavily loaded truck driving in city settings needs gears, in my opinion.


Let us know what happens.
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  #7  
Old 03-22-2010, 12:33 PM
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TennesseeMustangPerf TennesseeMustangPerf is offline
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Agreed. All in all, the taller the gears, the better the power is placed to the ground i.e. increase in acceleration, but the higher the gear also means that the truck will get a little less MPGs and see a little less top speed.
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Old 03-22-2010, 03:54 PM
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Originally Posted by TennesseeMustangPerf View Post
and see a little less top speed.
Top speed became less relavant to me with the advent of the overdrive transmission. I can have a ring and pinion ratio of 4.10:1 have 33" tires and still cruise 75mph at under 2500rpm.

Drop the transmission down into direct drive 1:1 ratio, you know the "high" gear of the glorious C6 Ford used for so long, and my engine speeds up over 25%. Back in the C6 days, 4.10 ring and pinions seemed to be associated with "rock-crawling" and "mud-boggin'." Ha! My how the times have changed.

We're about to dawn a new age with double overdrive...
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  #9  
Old 03-22-2010, 06:09 PM
blawknox977 blawknox977 is offline
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wow thankyou seminaryranger!! that gives me a lot to think about.

i have the auto transmission, tire size: 285/75/16r i have the standard 4.1:1 ratio gears everything is stock.

i know im not going to get dramatic changes in MPG but i was just looking for an improvement around +2 or so. i drive on the highway a good amount, couple times a week i drive about 60 miles round trip.

with that size tire a 4.56:1 ratio and considering the year and how weak the motor is maybe thats not to bad a combo.

anything else you need to know to help figer out a good combo?

and i have replaced most of those thing suggested, what are COD's and zerks??
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Old 03-22-2010, 06:34 PM
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alot of guys run 4:30 gears. in my opinion i would go that route. you probably not going to pick up any mpgs. if your 2wd factor $1000 bucks or less to regear. a tuner though will cost $400ish. if you real mission is mpgs go to a 265 or a 245 tire. if you like the looks of the 285 id try tuning first then go to gears. worst case senario the tuner can be sole for half to 2/3 the cost. while gears only cost a $100-200 and the labor to do it are the expensive part.
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Old 03-22-2010, 11:00 PM
moparfrkshw moparfrkshw is offline
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On my 03 250 5.4 with 82K, I get between 12.5 & 14 on the hwy between 60 & 70. I have gotten it to hit 15 running about 60 with the cruise set as well. I run about 55mi one way 5 days a week. We just did the tune up, ball joints & shocks all the way around.

If you are going for fast acceleration, the 5.4 sucks!!! It is a grandpa's truck when it comes to getting up to speed. If you are wanting faster acceleration you are going to just be wasting gas in it. I can tell when my hubby drives it cuz he accelerates like he is in our jeep......kills my mileage.
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  #12  
Old 03-23-2010, 12:25 AM
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Furian Furian is offline
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Quote:
Originally Posted by blawknox977 View Post
wow thankyou seminaryranger!! that gives me a lot to think about.

i have the auto transmission, tire size: 285/75/16r i have the standard 4.1:1 ratio gears everything is stock.

i know im not going to get dramatic changes in MPG but i was just looking for an improvement around +2 or so. i drive on the highway a good amount, couple times a week i drive about 60 miles round trip.

with that size tire a 4.56:1 ratio and considering the year and how weak the motor is maybe thats not to bad a combo.

anything else you need to know to help figer out a good combo?

and i have replaced most of those thing suggested, what are COD's and zerks??

You can use the RPM Calculator (link below) to determine if you want to change the gears in your axles. The automatic transmission (4R100) in your Super Duty has a "Transmission High Gear Ratio" of .71. Your 285/75R16 tires have a diameter of 32.76" or 33" rounded. If you enter the following values into the RPM Calculator, you can determine the RPM's at a given speed.

Miles Per Hour: 70
Tire Diameter in Inches: 33
Axle Ratio: 4.10
Transmission High Gear Ratio: .71

RPM: 2,077

If you change to 4.30 gears, the new RPM's would be 2,177. If it were me, I would not invest the money to change your 4.10 gears unless you plan to run taller tires (35" or 37") in the future.

RPM Calculator

COP = Coil On Plug - There should be a COP attached to each of the spark plugs on your engine. Sometimes these fail due to age and/or heat. They can be tested.

Zerk's - These are the "nipples" that are used to inject grease into ball joints, u-joints, etc. to keep the suspension and drivetrain from binding.

Also, look at the "Combo's" offered at 5 Star Tuning... Specifically, there is Combo 3 and Combo 4 that applies to your Super Duty. See link below for details.

http://www.5startuning.com/combodeals/
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Old 03-23-2010, 12:25 AM
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