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Tach Drive Distributor

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  • Greg S.
    Very Frequent User
    • July 31, 1995
    • 243

    Tach Drive Distributor

    I purchased a tach drive distributor that does not have an ID band to identify its original use. Can anyone identify the original year or intended use from the clues in the dissassembled pictures at the site listed below? I hope this link works.

    Daftar dan mainkan slot gacor dengan RTP tertinggi hari ini. VIPTOTO, situs terpercaya untuk cuan besar dari slot online!


    I believe it is pre 67 but I am not knowledgable about the differences.
  • Duke W.
    Beyond Control Poster
    • January 1, 1993
    • 15610

    #2
    Re: Tach Drive Distributor

    It's possible it can be IDed with the various numbers on parts. I don't see any numbers on the weights, which means they might be aftermarket. The springs look like GM. The shaft is "210", but it was not serviced separately - only with the cam as an assembly (I think weights and springs were also included.), and the same shaft was likely used with different cams, weights, and springs to come up with various centrifugal curves.

    The "047" breaker plate is OE.

    The numbers on the old vacuum advance control will narrow the range if it's original. What are the numbers? They are not readable in the photos. And check both sides of the weights to see if they have any stamped numbers.

    Duke

    Comment

    • Greg S.
      Very Frequent User
      • July 31, 1995
      • 243

      #3
      Re: Tach Drive Distributor

      I believe the vacuum can is 16-163. It's not where I can look at it right now. I don't think the weights have any numbers on either side. I am building a driver distributor for my 62 340 horse using your recommendation to use a B-28 8" vacuum can. My original dual point will be stored for use when being judged. Not quite on topic here. I am looking to improve cooling at idle in traffic on hot days. I am also trying to learn the differences in tach drive distributors. I have read that from 67 on the centrifical advance weight base had nylon buttons where the weights ride. This one has metal buttons. This distributor does not have the nylon button for the tach drive gears. I am not sure why.

      Comment

      • Edward M.
        Extremely Frequent Poster
        • November 1, 1985
        • 1916

        #4
        Re: Tach Drive Distributor

        The nylon button came into being in about 1971 if memory serves. If this distributor housing doesn't have a hole in the back side of the tach drive cross shaft, that would make it earlier than 1971.

        Comment

        • Duke W.
          Beyond Control Poster
          • January 1, 1993
          • 15610

          #5
          Re: Tach Drive Distributor

          I was hoping the VAC was 236 16. Double check when you look at the parts again. The 163 is a common replacement VAC, but since it requires up to 18" to pull to the limit, I don't even recommend it for 250 and 300 HP engines. The B28 is the functionally correct VAC to use on all mechanical lifter SBs.

          I also see some numbers on the bottom of the cam, but can't read them. What are they?

          Something else you can to is put the cam on the shaft and measure the amount of rotation freedom. It should be between 12 and 15 degrees, which corresponds to the 24 to 30 degrees of total centrifugal on C1 and C2 distributors. That will narrow the range.

          The cam was available separately and the stamped numbers are probably the last three or four part number digits, which will ID it and narrow the range of distributor numbers.

          Your '62 340 HP engine should idle better and deliver noticeably improved fuel economy with a B28 VAC. What will be the VAC vacuum source?

          Duke

          Comment

          • Greg S.
            Very Frequent User
            • July 31, 1995
            • 243

            #6
            Re: Tach Drive Distributor

            I will look at the vacuum can tonight. The numbers on the cam are faint but appear to be 536, 586 53x or 58x. The last number is very hard to see but appears to be part of a 6. There is also a CC below the number. The part looks to old and abused to be a Corvette Central repo part. The vacuum source plan is to put a T in the line to the wiper washer can. The source is off the base of the carb as is correct for a 62 340SHP. I also have a hollow carb stud which I could use.

            I also wanted to ask, the old vacuum can has what looks like a limit bushing on the linkage. The new can does not. Should I put the bushing on the new can linkage or leave it off?

            Comment

            • Duke W.
              Beyond Control Poster
              • January 1, 1993
              • 15610

              #7
              Re: Tach Drive Distributor

              None of those are a good match for the last three digits of the cams listed in my '77 vintage Corvette P&A catalog. Try rubbing the area with a Scotchbrite pad and use different light angles. Making a pencil tracing might also reveal the numbers more clearly.

              The B28 VAC should max out at 16 deg. @ 8" plus or minus one deg./" without a bushing. Check it on a dist. machine or on the car.

              Duke

              Comment

              • Wayne M.
                Expired
                • March 1, 1980
                • 6414

                #8
                If the rotating weight plate is 536 CCW ...

                ... which it looks like to me, then it might be from (but maybe not exclusively) a 1111069 ('64 or '65 L76). Reason I say that is because I purchased an over-the-counter "069" in 1980, with tag 0_D_23 (obviously a service unit) and it had this rotating points bump cam. Also, there were no nylon wear buttons for sliding weights.

                I have a total of 8 tach drive distribtors here [5 T.I. and 3 points], and not one of them has the rotating pole/points or auto cam (the part that is brazed to the shaft) whose stamped numbers relate to anything in the P&A30 catalogs. Deep in the bowels of Delco these numbers must have listed specs.

                Look at your cam driven gear; it is bevelled for reverse rotation !!

                As others have mentioned the fact that the cast iron housing is not drilled for and has no nylon thrust button places this part somewhere before mid 1970.

                As far as the nylon wear buttons on the weight plat tying to a specific changeover date from the metal (hardened ?) buttons, this is less conclusive. Other than the OTC "069" mentioned above, I have an almost NOS 1111296 8_B_23 with the buttons on the plate but not drilled on the tach drive thrust. Also a 1111267 9_D_14 (same situation), so in production, the weight plate nylon buttons could well have been introduced around 1967 (maybe others can narrow this down as I'm curious). Maybe it depended on application, as I also have a 1974 1112247 4_E_31 with no nylon wear buttons on weight plate.

                Another thing about stampings on rotating pole/points weight plates. Check link below....


                .... for the same "534" stamped on two different weight plate designs (one is for '71 LT1 (1112038) and the other is off a NOS ball bearing 1111263. So this number must have related to the slot length or other geometry of the plate itself, and not to the assembly on which is was installed. Note the shaft hole on the ball bearing unit (left) is larger and intrudes on the weight advance slot.

                Finally, the pic below is for Duke and/or Joe L. Notice it has the same patent # as your distrib., even though this one is for a points w/shield package, and the shape of the points plate is of different design than yours. I suppose that the patent applies to the function of this part and not the design modification for point shields.
                Attached Files

                Comment

                • Joe L.
                  Beyond Control Poster
                  • February 1, 1988
                  • 43193

                  #9
                  Re: If the rotating weight plate is 536 CCW ...

                  Wayne-----

                  The cam/weight base using the nylon buttons was first used for the 1968 model year in Corvettes. However, it was not used for all applications---only some. The use of both types of cam/weight bases continued through 1974, although I believe that most distributors used in the 73-74 period used the nylon button-type cam/weight bases.

                  Although the tach driven gear nylon thrust button was phased into use beginning in later 1970 or 1971 for both PRODUCTION distributors as well as SERVICE distributors of earlier part numbers, the nylon button-type cam/weight base was not generally phased into use for SERVICE distributors of earlier part numbers. In other words, if the original distributor didn't use the nylon button-type cam/weight base, the SERVICE distributor didn't have it, either, regardless of when it was made.

                  Why the use, especially the concurrent use, of the nylon button and non-nylon button cam/weight bases? I have no idea.

                  Also, the characters, apparently some sort of identifying series, found embossed on the auto cams is not related to the part number of the distributor or the shaft assembly. As you mention, I'm sure that is somewhere correlated, but the information is not provided in any reference that I have.
                  In Appreciation of John Hinckley

                  Comment

                  • Gerard F.
                    Extremely Frequent Poster
                    • June 30, 2004
                    • 3803

                    #10
                    Re: Tach Drive Distributor

                    Greg,

                    The picture below is a 67 original for a 327/300 base engine:


                    Did a little refinish on the vacuum can.

                    Here's what the centrifical cams look like:


                    Not sure what you have, but the pictures are for a 67 base engine.

                    Hope this helps,

                    Jerry Fuccillo
                    #42179
                    Jerry Fuccillo
                    1967 327/300 Convertible since 1968

                    Comment

                    • Greg S.
                      Very Frequent User
                      • July 31, 1995
                      • 243

                      #11
                      Re: If the rotating weight plate is 536 CCW ...

                      The Weight plate is definately stamped 53X. The X being so faint that I cannot tell for sure what the number is. My best guess is a 0 or a 6. It is not a 4. The number is stamped on the bottom, unlike the tops of your examples. I read somewhere that there are over 50 variations of these weight plates which are keyed to the advance requirements of various engine combinations. One more unknown for us to solve.

                      Comment

                      • Joe L.
                        Beyond Control Poster
                        • February 1, 1988
                        • 43193

                        #12
                        Re: If the rotating weight plate is 536 CCW ...

                        Greg-----

                        I think that you're thinking about the "autocam" (the piece brazed to the top of the mainshaft). There were a very large number of different configurations for different mechanical advance characteristics. There were also a large number of springs; not really all that many different weights, though. As far as the cam/weight base, there were more than a few configurations, but I don't think that there were anything like 50. In additon, many of the ones that do exist are functionally identical.
                        In Appreciation of John Hinckley

                        Comment

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