The bouncing comes from either binding of the cable or one of the magnets inside the speedo unit either losing its magnetism or is missing. More often than not, it is in the speedo cable. You are dealing with a 75+ year old part here and it will need a little TLC to get it working properly. If you used a grease, your best solution is to remove the drive inner cable and thoroughly clean it and lube it with a graphite lube. You can also use a very light oil like 3 in 1, but beware, it will very likely loosen any old lube in the sheath and your problem will probably return. Sometimes it is easiest to remove the entire cable assembly and thoroughly clean out all of the old lube that is in it, relube it and reinstall it. Grease, as was mentioned before, it is too thick and will cause bouncing. The best lube is a graphite lube. Messy but it works the best. Good luck with your repair.