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Way OT - Horizontal Driveshaft Alignment

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  • Way OT - Horizontal Driveshaft Alignment

    Hi Folks, Just completed a motor and trans swap in my little Datsun 510 and need to set driveline phase. Easy enough for vertical alignment using my handy dandy digital inclinometer, but I'll be damned if I can find a good way to measure the horizontal alignment. The engine and trans mounts were fabricated, so stock location and alignment brackets could not be used.

    I was thinking of using a laser pointer on the trans and pinion input set at 90 degrees by milling a pocket in old flanges. I could at least see where they were pointing and whether there was a huge distance on each side, indicating way out of alignment, but that doesn't allow me much accuracy.

    And, in case I am using the wrong terms again (as usual), I need help on the left/right alignment, not the up/down

    Any ideas?

    Many thanks, Derek G
    Last edited by derekg; 10-01-2011, 07:48 PM.

  • #2
    I would bisect (is that the right term...?) the engine by dropping two plumb bobs from the same spot on both sides. I would find the center line of the trans and use that center line established by the two centers and string a tight line back to the center of the differential. Then hang weighted strings over the drive shaft and insure the center string is directly between the two weights. Adjust as necessary. Any deviation in alignment can and probably will cause phasing boom at the least and vibration (up to severe) at the worst.


    • #3
      Years ago, when I was an instructor at a truck tech school, I had a lesson plan that took up 2 day of theory, one day of lab work, on drive line operating angles. For the Cliff Notes version go here:

      There will not be a quiz.



      • #4

        @Joe - I think I got it. Seems logical. The actual measurement of the between the lines would be done by ruler, so the accuracy of the lines, the ruler, my hand, and my bad eyes becomes the accuracy of the driveshaft. It will definitely get me in the ballpark. Thanks.

        @Rex - Thank you also. The link you sent shows the vertical alignment, which I am doing with a digital inclinometer. You wouldn't happen to have that old lesson plan showing the horizontal, would you

        Thanks, Derek G


        • #5
          Horizontal alignment follows the same parameters as vertical. Remember, you are measuring the transmission and
          rear axle pinion angles, not the driveshaft.

          The transmission output shaft and the rear axle pinion shaft need to be (essentially) parallel in both planes.



          • #6
            Rex is correct. If the shafts are parallel, the angles seen by the U-joints will be the same regardless of the horizontal and vertical offset.

            Make a plate that will attach to the rear yoke, and attach a laser pointer to it. Get it reasonable close, and it'll sweep a small circle on a target near the other yoke. Measure from the center of the circle to the center of the yoke.

            Then switch the pointer to the transmission yoke, and put the target near the rear end yoke. Compare the measurements, and adjust until they're the same. Then the transmission output and differential input shafts will be parallel.
            Last edited by winchman; 10-02-2011, 02:31 AM.
            Any products mentioned in my posts have been endorsed by their manufacturer.


            • #7
              Wonder if you could use a tailpipe expander to close off one end?
              mark costello-Low speed steel


              • #8
                I like winchman's idea but could you just not use a set of points from something like the "frame"?

                If it is stock (uni/unit body I think?) there will need to have been some reference points somewhere for collision repair (if needed)...if it is a fully made frame then to make the frame correctly there will have needed to have been some reference points as well...measure off these points and use math (triangulation) ?


                • #9
                  Both the diff pinion shaft and the trans output shaft need to be parallel horizontally and vertically within one (1) degree and do not need to be in line with each other. I have taken two (2) straight edges and put them on the tail end of the trans housing and end of the diff housing and then made the two straight edges parallel to each other by adjusting the trans tail mount. Or if you wanted to be real persnickedy you could put both of the yokes on the diff and trans and then put some round stock thru the yokes and measure between the round stock for parallel.