How to determine center of a repro argentine steering worm gear - NCRS Discussion Boards

How to determine center of a repro argentine steering worm gear

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  • Ian G.
    Extremely Frequent Poster
    • September 3, 2007
    • 1114

    How to determine center of a repro argentine steering worm gear

    Hi all,

    I'm getting up the nerve to tear down the steering gear on my 59 to check its condition and see if I need to rebuild. A while back, figuring I would need to replace the work gear no mater what, I preemptively bought a rebuild kit including the worm gear. I have since read "As the Worm Turns" PDF brought to us from the Corvette Forum by Dave Zuberer. This PDF documents the saga numerous folks from that forum and NCRS went through trying to figure out what was wrong with one poor man's (JPW) steering. In the end if was found that the readily available repro worms made in Argentina are not made to spec and invariably vary in center measurement which affects the steering adjustments needed.

    Within that PDF it shows how to measure the center of an original worm, by measuring the half-way point with calipers opposite of the cutout key. However it isn't clear to me how to measure the repro worm to check for irregularity since the machining looks different. The original appears to have a bit of a sharp "edge" and the repros a bit of a "flat" area. In my pic would I measure from the top arrow, the bottom arrow, or in between the arrows? Dependign how I measure, the worm's center appears more or less better.
    Also, I wanted to verify if I identified the key properly as the repro is a bit different there from an original as well. Pics below.

    Original worm measuring
    pa180063_7e3f85d6551d536d5f27429db9fa06b1e5dec454.jpg
    Original worm "key"
    pa180057_dc0f4b4d6a0d7977d19e3e751c9632213078f169.jpg
    repro worm "key" ?
    IMG_3710.jpg
    Repro worm
    IMG_3713.jpg
  • David H.
    Extremely Frequent Poster
    • June 30, 2001
    • 1526

    #2
    Re: How to determine center of a repro argentine steering worm gear

    Ian

    Isn't "center" just going to be lowest spot on worm?

    Dave
    Judging Chairman Mid-Way USA (Kansas) Chapter

    Comment

    • Richard M.
      Super Moderator
      • August 31, 1988
      • 11323

      #3
      Re: How to determine center of a repro argentine steering worm gear

      Ian,

      I remember that thread well. That's how we figured out all reproduction worm gears are different. Dave is correct. It's just finding center, but it takes a bit of work and pre-knowledge to get it right. You cannot just use the standard procedure in the Service Manual.

      Since it appears the end-face machining of the worm can vary, you'll need a different approach. When I did 2 of these Argentinian repros, the caliper measurements to find center were the very close to the same for both worms. It appears later machined lots, like yours, are different because of the machined end inaccuracies.

      You'll have to find it after assembly by "feel". I know this doesn't sound ideal but it will be the most accurate method.

      First set the shaft endplay to within spec. Endplay is the amount of force needed to turn the wheel without the worm/sector in play. This is done by adjusting the large bearing cup at the end of the steering box. Spec is 3/8 to 5/8 lbs. You can use a fish scale to measure.

      With the sector lash adjustment screw released several turns, center the steering wheel from the lock-to-lock positions. This will put you near worm center.

      Slowly bring the sector lash in a little at a time as you rotate the wheel each way, maybe 180* or so. As you get closer to center, much less. Continue bringing the lash in until you feel a slight drag as you rotate the wheel. Very lightly while turning so you don't stress the worm and sector roller bearing surfaces. They are only surface hardened. You'll feel center as you slowly turn the wheel in both directions.

      Repeat the process until you're certain you've found center. Using a checking scale, measure the tension at center to within spec(7/8 to 1 7/8 lbs). Tighten the lash screw locknut. Place a witness mark on the end of the shaft at the 12:00 position.

      All procedures and specs are in the ST-12 1953-1962 Service Manual, Section 9. HERE

      For those unaware of the reproduction worm/shaft assemblies, there is no witness mark(chisel mark @ 12:00) on the end of the steering shaft for worm center. It's not there because the worm is not made as originals due to the present manufacturing machining process, very different from the original process.

      Because the repro worm is unlike the original and that it's center may be offset, it could affect the Pitman Arm travel. If so you may need to adjust the drag link more or less than typical to gain proper front wheel steering center.

      A few photos below for reference.

      Rich
      Attached Files

      Comment

      • Ian G.
        Extremely Frequent Poster
        • September 3, 2007
        • 1114

        #4

        Comment

        • Roger W.
          Very Frequent User
          • January 29, 2008
          • 567

          #5
          Re: How to determine center of a repro argentine steering worm gear

          I purchased a new OEM worm shaft assembly years ago. Can this original part be used with the reproduction sector shaft and the other parts in the kit rebuild kit?

          Comment

          • Richard M.
            Super Moderator
            • August 31, 1988
            • 11323

            #6
            Re: How to determine center of a repro argentine steering worm gear

            Ian,

            Correct, the repro worm will probably not be equal, but.... Unequal LTL at the steering wheel will never be a problem because at no time will the steering wheel be in either CW or CCW extreme position with all steering components assembled. The steering knuckle "stops" in their castings at the front wheel assemblies will go to their max end positions and stop the road wheels from turning, long before the steering wheel goes full lock. This was likely a design feature that ensured the sector roller would never reach the end of the worm at either end.

            We figured this out back then with Dennis's issue. When in the car, the steering wheel only turns about 1 3/4 turns in either direction when the steering knuckles hit, either side. LTL at the steering wheel is much more by itself, around 2 1/4 turns IIRC.


            Originally posted by Roger Williams (48508)
            I purchased a new OEM worm shaft assembly years ago. Can this original part be used with the reproduction sector shaft and the other parts in the kit rebuild kit?
            Roger, Likely yes, as long as the assembly using the new worm shaft assembly was built to the same specs as the original. If it's a GM part, then I'd say yes.

            As far as I recall a conversation I had with Joe Calgano(longtime NCRS member and restorer) years ago, was that he was manufacturing some of the parts in the Argentinian kit for Corvette Central. I don't recall if it was the sector shaft/roller bearing assembly or not. He said he supplied some of the parts in the kits.

            My gut tells me the sector was made to the exact spec, but I cannot guarantee that. I think the only way you would know for sure is to assemble everything and "test" the assembly by going through the ST-12 procedures and specs to ensure there is no error in the assembly.

            Does your "OEM" shaft/worm assembly have a "chisel mark" at the top of the shaft. identifying worm center?

            ====
            Rich

            Comment

            • Ian G.
              Extremely Frequent Poster
              • September 3, 2007
              • 1114

              #7
              Re: How to determine center of a repro argentine steering worm gear

              They sell these kits with and without worm gears so you'd think they should go with an original worm, but maybe thats a bad assumption on my part. Thanks for the info Rich!

              Comment

              • Roger W.
                Very Frequent User
                • January 29, 2008
                • 567

                #8
                Re: How to determine center of a repro argentine steering worm gear

                Rich. Thanks for your reply. My shaft has the "chisel mark." I bought the shaft from a Chevy dealer years ago. The sector shaft was already no longer available from GM.

                Comment

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