Changing Rearend Gearing

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Nov 6, 2007 | 01:20 PM

#16

snurtle112

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Joined: Jun 2007

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bigrey...id go higher i run 44i tires and i run 5.38 and im at arouns 2k rpm at 65mph

Nov 6, 2007 | 01:23 PM

#17

bigrey6306

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thats pretty good revs at that speed... what engine you have?
what do you think 4.88? higher?whats next? 5.13 or something?

Nov 6, 2007 | 02:40 PM

#18

krewat

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Joined: Jul 2002

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From: Long Island USA

Quote:

Originally Posted by rugermack

Has anyone done a write up on a gear install ? I searched but couldn't find any.

Most likely because no one is willing to take the responsibility of you grenading your gears

With gears, if you know how to do them, you do them.

If you don't, pay someone to do it.

If you really REALLY want to do it yourself, the service manuals will tell you how to do it.

You need some precision tools, preferably have access to a hydraulic press, and lots and LOTS of patience.

There are no shortcuts. Sometimes there are. But not for the patience part

Nov 6, 2007 | 02:40 PM

#19

o'brien

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Joined: May 2007

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4.56 are fine up to 36inch, 37-38 is pushing it anything over 38', go to 5.13, over 42's go to 5.38 or bigger numerically.It's all about the grunt down low and with all the 5 and six speed transmissions now you won't suffer on the mpg.

Nov 6, 2007 | 02:53 PM

#20

redford

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From: Stephensville WI

This site does have a decent selection of calculators that will tell you exactly how to restore the effective gear ratio back to stock (or close to it).

https://www.ford-trucks.com/calculat.../p-tire_sizes/

For example, let's say you have 33 inch tires and a 3.73 differential ratio, but want 44 inch tires. Plug those number into the handy calculator, it tells you to change the differential ratio to 4.9733333333333 to return to a stock effective gearing. (4.88 would probably be about the closest you could find).

Nov 6, 2007 | 09:07 PM

#21

stroken

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38" tires...can any one tell me the rpm and mph with the following gears.... 4.56 and 5.13... I think 5.38 will be a little to large..thanks to all!!!

Nov 6, 2007 | 09:22 PM

#22

redford

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Joined: Sep 2000

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From: Stephensville WI

Quote:

Originally Posted by stroken

38" tires...can any one tell me the rpm and mph with the following gears.... 4.56 and 5.13... I think 5.38 will be a little to large..thanks to all!!!

You can do it yourself

with these calculators:

https://www.ford-trucks.com/calculat...php/p-mph_rpm/

Remember, you have a 0.71 overdrive on your transmission, so you'd calculate the overdrive first.

For example, a 5.38 gear times 0.71 = 3.82 final drive ratio. Using the site calculator, 38 inch tires with a 3.82 final drive would get you 2026 RPM at 60 MPH.