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Axle ratios and Gear Ratios

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Old 02-10-2017, 09:27 PM   #1
62 corvette nut
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Default Axle ratios and Gear Ratios

I'm "Corn Fused" (as my uncle Bill used to say. I have a 62 with a 327 - 340 HP - 4 speed positraction. The Corvette servicing guide (ST-12) on page 14-2 lists 3.36:1 regular ratio but it lists 6 different Positraction ratios. How do I determine what I have?

Also in the transmission section page (14-17) it lists 2 ratios for each of the first three gears. Again how do I tell what I have?

I know someone out there has the answer or can tell me how to calculate it. All help greatly appreciated, i've owned the car since 1968, but never payed much attention to the gearing, now i'm curious.
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Old 02-10-2017, 09:52 PM   #2
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see this one of many threads

http://www.corvetteforum.com/forums/...end-gears.html

also if rear is original it will have a cast date code and part# on drivers side on lateral front facing surface

opposide side there is a stamped code that reveals axle ratio. very difficult to see. scrub clean to see. find codes for vette on differernt vette websites.
codes for 62 chev may not match up with codes for 62 vette.

rear gears could have been changed so follow direction in suggested thread.

trans could be wide ratio
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Old 02-11-2017, 10:37 AM   #3
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Assuming the speedometer gearing is correct for the installed axle.

In forth gear axle ratio = revs @ 60 / 760.

All 340/360 HP engines ordered with the optional four-speed received the close ratio version (2.20:1 first gear).

Duke

Last edited by SWCDuke; 02-11-2017 at 10:40 AM.
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Old 02-11-2017, 11:59 AM   #4
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Simply turn rear wheels one revolution and count revolution of driveshaft. Revolution of driveshaft equals the ratio. Thus driveshaft turns 3.7 times, ratio is 3.70. This only works with positraction.
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Old 02-11-2017, 02:48 PM   #5
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Try what hope2 described.
I believe that typically the car with a close ratio trans (2.20 first gear) had a 3.70 rear gear. The 2.20 first gear and a 3.36 rear would be hard on the clutch and the driver.
Difficult to get the car moving.

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Old 02-11-2017, 11:52 PM   #6
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Quote:
Originally Posted by hope2 View Post
Simply turn rear wheels one revolution and count revolution of driveshaft. Revolution of driveshaft equals the ratio. Thus driveshaft turns 3.7 times, ratio is 3.70. This only works with positraction.


And if you don't have positraction differential, lock one rear wheel in place and turn the other rear wheel exactly two complete revolutions while counting how many times the pinion shaft/driveshaft yoke revolves and that will give you the gear ratio.
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Old 02-12-2017, 05:04 AM   #7
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Quote:
Originally Posted by ohiovet View Post
Try what hope2 described.
I believe that typically the car with a wide ratio trans (2.20 first gear) had a 3.70 rear gear. The 2.20 first gear and a 3.36 rear would be hard on the clutch and the driver.
Difficult to get the car moving.
lol... (2.20, CLOSE ratio...)

Bill

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Old 02-12-2017, 03:17 PM   #8
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Quote:
Originally Posted by ohiovet View Post
I believe that typically the car with a wide ratio trans (2.20 first gear) had a 3.70 rear gear. The 2.20 first gear and a 3.36 rear would be hard on the clutch and the driver.
Difficult to get the car moving.
True that - that's the way my '67 was built. OTOH, I lived with it that way for about 35 years, until I put in a Tremec TKO 500 with a 3.27 1st gear and a .67 5th!
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Old 02-12-2017, 10:03 PM   #9
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Quote:
Originally Posted by ohiovet View Post
Try what hope2 described.
I believe that typically the car with a wide ratio trans (2.20 first gear) had a 3.70 rear gear. The 2.20 first gear and a 3.36 rear would be hard on the clutch and the driver.
Difficult to get the car moving.
If you have how do you like it? What are the Pros and Cons? Who installed it for you, I'm just down the road from your location. Approx. cost to install.What about the clutch (Hydraulic or Manual, Why?

Thanks,

Marty
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Old 02-16-2017, 08:43 PM   #10
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Quote:
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lol... (2.20, CLOSE ratio...)

Bill
Bill I tried to send you a PM, obviously i'm doing something wrong.

Bill,
I spoke with 'Frankie the Fink" on the phone this afternoon he suggested I call you about the 5 speed transmission that you installed in your 62. He says it was from Silver Sport and that it shifts slicker then the Tremec TKO 600. I think he said it was an "RS" model. What is different about this transmission versus the TKO 600.

I am going thru the thought process of installing a five speed in place of my T-10 "Rock crusher".

How long did it take to install? What was the price comparison between the two kits? Thanks for your help.

Marty
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Old 02-16-2017, 09:45 PM   #11
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2.20 is a CLOSE ratio
2.56 is a WIDE ratio

Last edited by DZAUTO; 02-16-2017 at 09:46 PM.
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