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Torsion Bars

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  • Torsion Bars

    I am investigating the feasability of machining some torsion bars for a streetrod project that I am doing. Does anyone have info about what material and sizing for spring rates. Any help would be appreciated.

  • #2
    i wouldn't re-invent the wheel on this one. go to a salvage yard, plenty of cars and trucks still use them. if you're building a rod you'll have plenty of better things to spend time on.


    • #3
      Ditto what Steve says.

      Baring self punishment.....Ummmmmm. What about spring steel? I hope you have access to heat treating facilities too.


      • #4
        I haven't made any torsion bars but here is the formula for determining spring rates:

        lbs. per inch = 2,200,000 x d(4) divided by L x l(2)

        The number in parentheses are powers of that number (i.e. diameter to the fourth power)

        Where L = bar effective length, d = bar diameter, and l = lever arm length.

        From what I have been able to ascertain, the material of choice is either 4340 or 4130 and the heat treatment is to 35 on the Rockwell C scale.

        The real fun is making a broach for the splines. It's not impossible, I've done that.

        Hope this helps.

        Guess I'm not doing this right...I suppose that I should be joining the others in telling you to just buy some parts. By all means, check out what is available off of the shelf, but if that does not prove satisfactory or if you just want a challenge...I say go for it!

        I haven't ever figured out how you learn by NOT doing something.


        • #5
          I'm not building a junkyard streetrod. Nor would the spring rates be correct. I was basically seeing if anyone had any differant info than I. Thanks anyway.


          • #6
            No one said you were, You asked for advice ,you got it and some suggestions.
            some people are so Thin skinned.


            • #7

              I don't know if the info that I presented is different than what you have or not. What info do you have?


              • #8
                I think you answered his question completely George.


                • #9

                  Here are some junkyard parts that make a pretty decent looking and great working front end. This used to be a pretty popular adaption back in the early days. It uses the front suspension parts from an XKE Jag along with some homebrew fabrication. The Jag uses a torsion bar for a springing medium. It is just inside the lower control arm pivot shaft on the right side in the photo. I don't remember the specs on the bar but would guess about a 3/4" diameter and an effective length of about 30". The lever arm is fairly long as it is length of the lower A arm.

                  One neat thing about the Jag bars is that the splines on one end are different than the other end. 25 and 26 splines if I remember correctly. That means that the ride height can be adjusted almost infinitely without an adjustable anchor. Just slip the bar out and rotate it however much you need.

                  This setup was on the front of a '32 Ford chassis.


                  • #10
                    They come in, ask a question, and when they don't like the answers they leave in a huff.
                    Same ole song, different tune.


                    • #11
                      IOWOLF, I thought that machinists were on this site not junkyard divers. I am not in a huff just that I am a experienced chassis builder of some 40 years experience and with high end cars I do not use junkyard parts.


                      • #12
                        There are both here, if you searched the threads you would know that.
                        You haven't answered Georges Question,yet.

                        With 40 years exp. why ask any thing here, It was not a machinist type question any way,IMO.


                        • #13
                          Hi George. Not that it matters much but my formulas show a constant of 1,178,000.... JRouche
                          My old yahoo group. Bridgeport Mill Group



                          • #14
                            "It was not a machinist type question any way,IMO"

                            Here, I'll add the word lathe in there, that should make it OT JRouche

                            "M-5 TORSION PENDULUM AND LATHE"

                            My old yahoo group. Bridgeport Mill Group



                            • #15

                              The information that I have came from Paul Van Valkenburgh's book "Race Car Engineering and Mechanics". As to which one is correct, your guess is a good as mine. As you say, it doesn't much matter as I don't think that ecdperf isn't too interested in really learning anyway.

                              I wish that he had stuck around and shown some of his work as I have been fooling around with this stuff since 1959.

                              He might have had some interest in this design exercise as it is torsion bar based.

                              On second thought, he probably wouldn't be interested as the design is for a lowly T-Bucket and he apparently only builds mega-buck stuff. At least the design does not use any junkyard parts.