1985 Silverado speedometer cable problems

[Texas Agman]

My real nice '85 Silverado has 230,000 miles on it and the speedo cable keeps coming apart according to my local rural mechanic. I was told a couple of times that the cable is in two sections and that they separate, rendering the speedometer useless. I checked most of my usual supply houses for parts without success. Have any of you had speedo issues with cables and the parts necessary to change the speedo readings when the rear axle ratio was changed ? This is a first for me and I don't have a clue what I am talking about. Thanks for pointing me in the right direction.