Depends entirely on whether the speedo cable broke or its something else thats gone wrong. If the inner cable did break, it could simply have worn through the polyethylene cable liner, which themcatches the inner cable and snaps it. Adding a new inner cable into a worn outer, greased or not, will very likely break the new inner cable too. When I did this many years ago, the new inner cable did not survive a ride around the block. Complete new speedo cable assemblies are now teflon lined and work much more smoothly, likely also living longer.
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