1957-58 Corvette Powerglide gear ratio - NCRS Discussion Boards

1957-58 Corvette Powerglide gear ratio

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  • David B.
    Very Frequent User
    • March 1, 1980
    • 689

    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.
  • Mike M.
    NCRS Past President
    • May 31, 1974
    • 8383

    #2
    Re: 1957-58 Corvette Powerglide gear ratio

    the differential in 57 250 hp PG vet vin 1093 was almost certainly the original center section and it's ring and pinion(with GM identifiers stamped therein) is a 3.55:1 setup. mike

    Comment

    • David B.
      Very Frequent User
      • March 1, 1980
      • 689

      #3
      Re: 1957-58 Corvette Powerglide gear ratio

      Thanks Mike for your input, only 1392 owners to go before a revision can be made in the 7th edition of the 56-57 Judging Manual.

      Comment

      • Jim N.
        Infrequent User
        • December 1, 1992
        • 17

        #4
        Re: 1957-58 Corvette Powerglide gear ratio

        My '57 250hp PG car #4090 also has the 3.55 gears. It was owned by a family member for more than 50 years so I'm sure it is original.

        Comment

        • Joe L.
          Beyond Control Poster
          • February 1, 1988
          • 43221

          #5
          Re: 1957-58 Corvette Powerglide gear ratio

          Originally posted by David Bartush (3288)
          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.

          David-------


          As far as I can tell, all 1955-61 Corvettes with Powerglide were originally built with a 3.55:1 rear gear ratio.
          In Appreciation of John Hinckley

          Comment

          • Jack M.
            Extremely Frequent Poster
            • March 1, 1991
            • 1155

            #6
            Re: 1957-58 Corvette Powerglide gear ratio

            Looking at the AMA data contained in the 'Information Kits' from the GM Heritage Center (may not be 100% correct), it confirms the 3.55:1 axle ratios for Powerglide transmissions in both the 1957 and 1958 Corvette.

            1957: Page #29 & #31
            1958: Page #14 & #28

            Comment

            • Gary C.
              Administrator
              • October 1, 1982
              • 17662

              #7
              Re: 1957-58 Corvette Powerglide gear ratio

              Dave,

              The chart on page 214 is an explanation of the rear axle ratio codes stamped into the pumpkin.

              Gary
              ....
              NCRS Texas Chapter
              https://www.ncrstexas.org/

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              Comment

              • David B.
                Very Frequent User
                • March 1, 1980
                • 689

                #8
                Re: 1957-58 Corvette Powerglide gear ratio

                Originally posted by Gary Chesnut (5895)
                Dave,

                The chart on page 214 is an explanation of the rear axle ratio codes stamped into the pumpkin.

                Gary
                ....
                Gary,
                If that is the case the chart is very misleading or simply incorrect! To further quote the previous mentioned 149 page Dealer publication:
                "1957 Corvette with 3-speed close ratio transmission has an axle ratio of 3.70 with an optional axle ratio of 3.36"
                Since the 3.36 ratio is an option NO particular prefix can be designated. Would recommend changing chart to:
                1956-57 AE 3.55:1 std Powerglide
                Would simply list 3.36:1 as an option, ditto for 1958.

                Comment

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