Actually it looks like there are 3 lengths of spring. Two for 1982 and later models and one for models prior to 1982 (Mine is a '79). I went out and measured the lengths of the new springs and both are 100 mm. Since the pre '82 model length is not specified I'm guessing that I have the correct length spring. Could it be that the slot in the attachment bracket has elongated with wear over the years?