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5/20/10 12:49am - Original Message: 'How to figure out gear ratio'
brightbox
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Lake Villa, IL - USA

Vette(s):
1972 Coupe 454 4-speed. Original, 69,000 miles.

Joined: 10/27/2009
Posts: 2
From what I've read, the differential case on my 72 vette should have a production code stamped on it. The first two letters indicate the gear ratio. For example, AA would indicate 3.55:1.
 
From under the car, I've tried to find the production code, but I don't see it.
 
Can anyone tell me where it's located on the differential case? (Front, back, left, right, etc.)
 
Thanks!
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5/20/10 8:06am - Reply: 'How to figure out gear ratio'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 19449
Check the code location/description out here...



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5/20/10 10:42am - Reply: 'How to figure out gear ratio'
VetteSpecialties
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Mounds View, MN - USA

Vette(s):
70 LT1 coupe, 69 350 HP coupe, 69 390HP 427 coupe, 71 LS5 convert, 85 coupe, 93 coupe

Joined: 5/24/2007
Posts: 1031
Then, since your car is almost 40 years old, you might want to count the ratio anyway.  Jack up both sides of the rear and make sure both wheels turn together.  Then turn the wheels one turn, and count how many turns the driveshaft turns. 

Larry


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5/22/10 5:46pm - Reply: 'How to figure out gear ratio'
JMB Gold Member
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Cohasset, MA - USA

Vette(s):
1968 Black Prime Coupe, 427 custom built, 4 speed (M20), 3:36 rear end, Recaro seats, Intro wheels, Nitto tires, and Flowmasters. Restoration awaiting painting.

Joined: 1/5/2004
Posts: 36
You can multiply miles per hour times 1000 and divide by the engine RPM. For a 3.08:1 the ratio is 25.6, for 3.36:1 is 23.1, for 3.55:1 is 22.2, for 3.70:1 is 21.3, for 4.11:1 is 19.2, and for 4.56;1 is 17.0. Do it at different speeds and in different gears and you should get a pretty good average.



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5/24/10 1:35pm - Reply: 'How to figure out gear ratio'
VetteSpecialties
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Mounds View, MN - USA

Vette(s):
70 LT1 coupe, 69 350 HP coupe, 69 390HP 427 coupe, 71 LS5 convert, 85 coupe, 93 coupe

Joined: 5/24/2007
Posts: 1031
That method depends on tire size.  The only correct way is to count the turns.

Larry


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5/24/10 3:36pm - Reply: 'How to figure out gear ratio'
brightbox
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Lake Villa, IL - USA

Vette(s):
1972 Coupe 454 4-speed. Original, 69,000 miles.

Joined: 10/27/2009
Posts: 2
Thanks everyone.
 
With the information you provided I was able to find the production code and then I verifiyed the gear ratio manually by turning the tires.


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5/25/10 2:40pm - Reply: 'How to figure out gear ratio'
anips
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sonoma, CA - USA

Vette(s):
72 LT-1 AC coupe,69 l-36 coupe

Joined: 8/9/2002
Posts: 783
larry must have spent some time in wreaking yards, me to.

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7/16/10 5:39pm - Reply: 'How to figure out gear ratio'
VeteransVette73
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Flat Rock, MI - USA

Vette(s):
L48 coupe, red on red.

Joined: 4/4/2010
Posts: 14
I tried Larry's post (marked rotor and drive shaft) and it came out to be 3 and a 1/4 turns.  The 73 vette did have a 3:26.  The AW273E2 on the rear comes up in reference book as a 3:08.  The build sheet for the motor has major upgrades but I have no paperwork for anything else.  Think it could be a gear swap? 

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7/16/10 10:23pm - Reply: 'How to figure out gear ratio'
anips
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sonoma, CA - USA

Vette(s):
72 LT-1 AC coupe,69 l-36 coupe

Joined: 8/9/2002
Posts: 783
IT USUALLY NEVER COMES OUT PERFECT, YOU SHOULD ALLOW FOR SLOP.

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7/17/10 1:05pm - Reply: 'How to figure out gear ratio'
philip
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Marana, AZ - USA

Vette(s):
1982 Silver Blue

Joined: 4/8/2010
Posts: 104
[QUOTE=anips]IT USUALLY NEVER COMES OUT PERFECT, YOU SHOULD ALLOW FOR SLOP.[/QUOTE]

x2 it is probably the stock 3.08 gear set.


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