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No longer Maching out...
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Discussion Starter #1
Hey guys, my car came with gears in it and the dealership had no idea what they were...

before I tuned my car it would stay around 1800 @ 55

but I put 18' wheels on it and changed the tire rev. per mile, I was thinking the gears seem like 3.73's but now when I'm driving 55 the tach says around 2k, and says 2500 @ 75...

What does it sound like to you?
 

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No longer Maching out...
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Discussion Starter #4
I've already checked the tire size differences...but the new tires are 285/35-18
 

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I wanna SPRAY!
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I'm gonna guess 3.73's also. My 5 speed with 315/35-17's cruises around 2500rpm at 75mph also.
 

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I'm gonna guess 3.73's also. My 5 speed with 315/35-17's cruises around 2500rpm at 75mph also.
+1
Plus I'm pretty sure 4.10s are closer to 3k on the highway around that speed. Mine are 3.73s and that's what I get as well...
 

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US Air Force (retired)
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Tire sizes and speedometer corrections... It's really easy to find out. Put the car in neutral and chock the front tires. Jack up the back. Place a mark on the driveshaft and one on the tire. Turn the tire one complete revolution. Count the number of times the driveshaft goes around. 3 1/4 = 3/27 gears. 3 1/2 = 3.55 gears. 3 3/4 = 3.73 gears. And, a little over 4 turns is 4.10 gears.

This is the only way to know for sure without taking apart your differential.
 

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Punching Throats
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I have an the same rims and 285 in the rear and i'm pullin the same rpm's as you.......I was told i had stock gears from the 2nd owner.....WTF!!!!
 

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The motive 3.90 aren't by Ford Racing which could be why it's stumping the mechanics. Also they require special instructions to be installed properly otherwise you can end up with a bad gear whine... while you're testing the driveshaft check for just under 4 turns. I'm curious :p
 

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Discussion Starter #11
I have an the same rims and 285 in the rear and i'm pullin the same rpm's as you.......I was told i had stock gears from the 2nd owner.....WTF!!!!
who the hell knows man...the way I'm thinking is that there is no way my car should be turning 2k at 55-60 with the stock gears
 

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Could be 3.55's since the rmps went up after it was tuned to 3.73's
 

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Discussion Starter #13
I never tried that...I could try the 3.55's tune

I'm just getting tired of messing with the tuner lol
 

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You could always take out the differential, it's stamped right on the top of the pinion
 

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Discussion Starter #16
haha...I'm pretty sure there's not an eaton rear end in it! lol

I'll check it out tho
 
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