1957-58 Corvette Powerglide gear ratio
Is 1957-58 Powerglide Corvette production gear ratio 3.36:1 correct?
After reviewing the latest 6th edition of the 56-57 Judging Manual I noticed the 3.36:1 ratio was still being listed as correct. However, a footnote under the ratio chart (pg 214) now seems to imply this may be incorrect. I would agree with that footnote and believe the 3.36:1 ratio was Never meant for production automatic 57-58 Corvettes. This error could possibly be the result of Technical Service Bulletin DR #272. This bulletin previewed identification of the prefix numbers for various options of the up coming 57 model year. Under Rear Axle Prefix & Numbers the 2934 series (Corvette) with powerglide is listed as being equipped the 3.:36:1 gear ratio with the stamped designation AE. To help explain how this error might have occurred, one needs to look at another late '56 Chevrolet publication sent to Dealers. This 149 page publication outlined the "the more important design changes from 1956 to be effective at the start of 1957 production". On page 7 under the heading: Rear Axle and Suspension -Passenger car there is a beginning notation. "New rear axle gear ratios adopted as a result of the 14-inch wheel which requires less gear reduction". Simply stated, all 1957 powerglide & turboglide equipped Passenger Cars would have a 3.36:1 gear ratio. It appears the Tech Bulletin writer was unaware the Corvette model continued to use the 15 inch wheel with no change from 1956. If this was the case I am certain the listing would have remained 3.55:1 also with the stamped AE designation. To highlight the 3.55:1 ratio as being correct, note page 268 of the 6th edition of the JG which copied the original 1957 AME specs and 3.55:1 is listed for the production automatic Corvette. While not necessarily further proof, the 1957 Master Parts Catalog lists the 3.55:1 ratio as correct for the '57 Corvette with little or no mention of the 3.36:1 ratio which was considered an option.
After reviewing the latest 6th edition of the 56-57 Judging Manual I noticed the 3.36:1 ratio was still being listed as correct. However, a footnote under the ratio chart (pg 214) now seems to imply this may be incorrect. I would agree with that footnote and believe the 3.36:1 ratio was Never meant for production automatic 57-58 Corvettes. This error could possibly be the result of Technical Service Bulletin DR #272. This bulletin previewed identification of the prefix numbers for various options of the up coming 57 model year. Under Rear Axle Prefix & Numbers the 2934 series (Corvette) with powerglide is listed as being equipped the 3.:36:1 gear ratio with the stamped designation AE. To help explain how this error might have occurred, one needs to look at another late '56 Chevrolet publication sent to Dealers. This 149 page publication outlined the "the more important design changes from 1956 to be effective at the start of 1957 production". On page 7 under the heading: Rear Axle and Suspension -Passenger car there is a beginning notation. "New rear axle gear ratios adopted as a result of the 14-inch wheel which requires less gear reduction". Simply stated, all 1957 powerglide & turboglide equipped Passenger Cars would have a 3.36:1 gear ratio. It appears the Tech Bulletin writer was unaware the Corvette model continued to use the 15 inch wheel with no change from 1956. If this was the case I am certain the listing would have remained 3.55:1 also with the stamped AE designation. To highlight the 3.55:1 ratio as being correct, note page 268 of the 6th edition of the JG which copied the original 1957 AME specs and 3.55:1 is listed for the production automatic Corvette. While not necessarily further proof, the 1957 Master Parts Catalog lists the 3.55:1 ratio as correct for the '57 Corvette with little or no mention of the 3.36:1 ratio which was considered an option.
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