If you try a pickle fork it is important to use the correct size. The first time I used one on my car it was not the right size and I never got the joint to separate but then I tried a fork that fit properly and it only took 3 or 4 hits to separate. As stated if you push on the end of the threaded portion it can cause it to tighten in the taper but a pickle fork stretches the taper helping it to release.

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1983 300SD
200000miles