I don't really remember if the car was running or not, try it without it running. If it does not work, then try it while its running. So, you should have the tool holding up the rod so that the knob can be screwed on.
-Joe

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'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.