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gear ratio on 63 lark

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  • gear ratio on 63 lark

    Is there any way I can find out what my gear ratio is?

  • #2
    crawl under the car and scrape the grease off the diff cover. there should be one or two tags attached to the bolts holding the cover on. One of them should indicate the gear ratio, and if a second one is present it will say "45B" or "45C" indicating a Twin Traction (limited slip) differential.

    If the tags are not present, put the rear axle on jackstands and count tire rotations vs. driveshaft rotations. Available rear axle ratios would be 3.07:1, 3.31:1, 3.54:1, 3.73:1, 4.09:1. I believe the standard ratio for a '63 4-speed would be 3.31:1, but since yours is an R2, I'm not certain of that (green pages in parts book do not indicate what the standard ratio would be; 3.31 is the standard ratio for a '63 J-body V-8.)

    Obviously if the rear end is a TT unit when you turn one wheel the other wheel will turn in the same direction; if it is not, it will likely turn in the opposite direction so you will have to chock one wheel to count the driveshaft rotations (and then divide by two)

    If the ratio tag is present but not the "45" tag, if you remove the fill plug you can see if it is a TT without jacking the rear up by just looking in the hole. If the carrier is right up against the hole, so you can barely poke your finger in to the first knuckle, then it's a TT unit.

    hope this helps...


    55 Commander Starlight
    55 Commander Starlight


    • #3
      Hey thanks Nate,

      It gives me an excuse to have to go out in the garage and spend time out there and...
      It is a 3.31 if anyone was wondering


      • #4
        That is a surprise. Most of the R2 four speeds were 373 from what I have noticed

        58 Packards
        62 & 63 Larks