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1961 rear axle ratios

harland

Well-known member
Joined
Jan 9, 2007
Messages
63
Location
colorado
Corvette
1961 fawn beige convertible
Good morning, wonder if I could get some help understanding why Chevrolet used, per the owner's manual, a 3.36 :1 ratio for the 3 speed manual, but a 3.70:1 ratio for the 4 speed . I read that the powerglide had a 3.55:1 ratio and I know that usually automatics have taller rear ends , though I confess I don't know the mathematics involved. Your patient education is appreciated. Harland
 

Tom Bryant

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Administrator
Joined
Nov 9, 2000
Messages
7,206
Location
Edgerton, Ohio, United States
Corvette
1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
I suspect that the ratios were intended to give the Corvette a little better off the line performance. In that time period it seems like in full size passenger cars if you got a V8 with Powerglide you got a 3.08 as standard. The low gear ratio in a Powerglide is very much a compromise since high is 1:1. 6 cylinder Powerglides had a lower low gear than V8s also and lots of guys swapped them for better performance in drag cars. I believe that the 3.55 was used strictly to give the Corvette better off the line performance with the 2 speed trans.

I don't have the info in front of me right now but I believe that the 3 speed also had a lower 1st gear than the 4 speed so it used a taller rear axle. I think that before 1962 all 4 speeds were 2.20 1st gear ratios and in 1962 there was a lower 2.54 available depending on engine (250 or 300) and option box checked. The lower 2.54 would be easier to get rolling with the 3.36 than the 2.20. Also the 3 speed car wasn't considered to be as high a performance car as the 4 speed. Full size cars in the mid to late 50s usually got the 3:70 with a V8 or 6.

My 1959 has a non-original 3.36 installed and with the 270 horse engine it doesn't like to roll away from a dead stop without some clutch slipping. I had a 3.70 in it that died and it was a breeze to get rolling.

Tom
 

wallyknoch

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Joined
Nov 9, 2002
Messages
457
Location
Dearborn
Corvette
One owner unrestored Black 1962 FI Corvette
Hi Tom,

Your probably correct on all your talking points but nearly anything under the sun was available from a 3.36-4.56. I would guess that dealer ordered cars for inventory purposes would have followed the advertised recommendations or general purpose gears as opposed to special orders as I did on all my Vettes that were either 4.11 or 4.56.
 

harland

Well-known member
Joined
Jan 9, 2007
Messages
63
Location
colorado
Corvette
1961 fawn beige convertible
rear axle ratios

Thanks for the info. As I live in hilly country in CO, I won't be tempted to try for any taller rear ends. I think the big issue with them related to top end speed and lower RPMs. I don't feel comfortable driving a 1961 Corvette very fast-65, maybe 70, but that's it. Why chance injuring it on the super highways with so many bad drivers all around you. I didn't see the auction, but a fellow tells me a white 1961 Corvette with an accessory hardtop, small engine version, with a non matching number status, went for over $100K and that is something! That is amazing. Regards, Harland
 
Joined
Jan 1, 2002
Messages
7,246
Location
Washington, Michigan
Corvette
'67 Marina Blue Convertible
Because through 1961, the 4-speed was only available as a close-ratio transmission, with a 2.20:1 1st gear; that ratio doesn't work very well on the street with anything less (lower numerically) than a 3.70 axle.

:beer
 

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