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Old 09-18-2013, 10:00 AM   #1
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gear/tire question... got the best of me.

So I have spend the last 2 days trying to determine what gears i'm running, and being a OCD I just cant figure it out exactly. I've got a 2003 Jeep wrangler X 4.0l I6 5 speed manual with a dana 35 rear. For the longest time I thought they were 3.73s but when requested my build sheet based off the VIN it said they were 3.07. It dropped my jaw because they don't feel like 3.07 at all. I've done 3 different formulas, and checked for the tags that went there, and all the formulas come out to something different. I read somewhere if it has the towing package it will have 3.73, and I don't know if mine has it or not but its got a uhaul hitch that is bolted to the frame.

I've got 31x10.50x15 bfg all terrains that measure about 29.5 inches in diameter.
when im in 4th (1:1) going 60 mph i'm pulling 2250 rpm
when im in 5th going 60 I pull about 1750 or 1800 rpm

hope someone can help me..

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Old 09-18-2013, 09:36 PM   #2
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Not the way to do it but if all measured accurately in 1to1tranny gear

Your distance traveled per minute at 60 mph is one mile so 5280 feet

Rpm x diameter in feet x pi all divided by distance in feet is the ratio

So if in 4th 2250 rpm at 60 mph

Ratio= 2250 * [29.5/12] *pi /5280 =3.29

The way you really find ratio

Jack up one back wheel if you have an open Duffy

Block front wheels put transfer case or tranny in neutral leave one back wheel on the ground release park brake

Put chalk mark on rear drive shaft u joint and chalk mark on bottom inside jacked up tire

Slowly turn drive shaft counting rotations while making jacked up tire turn two full rotations

The rotations of driveshaft to get the two tire rotations is the ratio ie if you turned drives shaft almost 4 and an eight rotations you have 4.11 gears

If you have limited slip jack up both rear wheels so they can both spin together and count driveshaft rotations for one full tire rotation to get ratio
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