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I hope everyone is having a terrific Saturday morning. Many will be dubious upon reading this post, but I am attempting to repair the unrepairable return spring on my speedometer needle. Obviously, I am abundantly aware that recalibration will be required (purchasing the necessary equipment). Conventional wisdom will obviously dictate that I outsource this exercise, however, I find it to be quite cathartic.
Seeking a replacement spring from a suitable donor/carcass, please find the attached.
Last edited by Kevin Ritter; 08-19-2023 at 11:40 AM.
Those look like common garden variety clock springs as found in millions of old windup alarm clocks in assorted diameters and coil counts. If you can't locate an exact replacement from a donor speedo, you might try the local thrift stores for old windup clocks or even eBay: https://www.ebay.com/sch/i.html?_fro...acat=0&_sop=15. I think most anything that would fit will suffice as a return spring so long as it is not so strong as to bounce the needle off the peg when it returns to zero. So not the mainspring but rather the balance wheel or striker springs.
Those look like common garden variety clock springs as found in millions of old windup alarm clocks in assorted diameters and coil counts. If you can't locate an exact replacement from a donor speedo, you might try the local thrift stores for old windup clocks or even eBay: https://www.ebay.com/sch/i.html?_fro...acat=0&_sop=15. I think most anything that would fit will suffice as a return spring so long as it is not so strong as to bounce the needle off the peg when it returns to zero. So not the mainspring but rather the balance wheel or striker springs.
Absolutely brilliant response, thank you for taking the time to compose. As you may have noticed from the picture, it is the smaller of the two return springs. The smaller spring is responsible for the very last portion of the needle's journey back to zero. i'm curious as to the importance of spring tension with respect to resistance in the movement of the needle. I suppose that in a pinch, I could count the number of coils and gauge of metal. So in clock parlance, the spring would be referred to as a "return spring correct"?
Absolutely brilliant response, thank you for taking the time to compose. As you may have noticed from the picture, it is the smaller of the two return springs. The smaller spring is responsible for the very last portion of the needle's journey back to zero. i'm curious as to the importance of spring tension with respect to resistance in the movement of the needle. I suppose that in a pinch, I could count the number of coils and gauge of metal. So in clock parlance, the spring would be referred to as a "return spring correct"?
Yes, it would be a return spring and would be smaller than the main spring because it must not overcome that spring that is helping advance the needle upward as speed increases. My guess is that virtually any spring will assist in returning the needle to zero so long as it is not too strong to overcome the force driving the needle upward as the vehicle speed increases.
You could select a replacement spring by sight alone by looking at the number of coils (the more, the weaker the spring action) and the width of coil material in both thickness and depth (the thinner the coil in both dimensions, the weaker the spring action).
08-19-2023, 11:37 AM
1982 Porsche 928 Speedometer Rebuild
