I had the same thing happen in my 1975 300D, a few years ago. It is, in fact, the speedo cable. The lubrication inside of the cable dries up after many years and starts to make the screeching noise until it warms up, thereby letting the grease left do its job. I have been told the way to fix this is to replace the cable, for most cannot be lubricated. Hope this helps.


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Chris
'87 300E