Midshaft tool like quickmick descibed is the best and easiest. I sell them for 25.
If not, you need the hold midshaft with a wrench and carefully heat the back of the aluminum coupler and it will release.
Be careful not to heat the shaft at all or you will cook the midshaft grease seals, etc.
Heat and, although I got ridiculed, candle wax or bees wax on the threads when it's hot. Heat will pull the wax into the threads and ease the removal. An old mechanics frozen bolt trick.
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