I first ordered a Hirschmann mast with a serrated chord since the chord on my existing antenna is serrated. When I went to install it, it wouldn't fit because the base of the mast had a compression sleeve rather than threads that would screw back into the motor unit. The smooth chord mast has the threaded base, so I ordered it. I read on a thread here that a smooth or serrated chord will work. I also thought that maybe 33 years of teeth on a smooth chord would serrate it enough to make me think that it originally came that way, the serrations were very shallow. The motor pulled maybe 7/8's of the chord in, but it wouldn't push it back out. What am I doing wrong? Thanks

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'81 300SD