My neighbor got a JD model 39 sickle mower, but we haven't gotten it hooked up and in operation yet. There is a part of the machine that I'm really curious about, as to when and how it works.
There is a large spring connected to a shackle, and that shackle appears to slide up and down an arm that's about a foot long. Under what circumstances does the shackle slide on the arm?
Part encircled in red in your photo is long to allow lift clevis to slide the length of part if cutter bar hits an obstruction & cutter bar "breaks back" from spring loaded catch encircled in green.
Okay, makes sense now. Once we see it in action, we might experience it although the fields are pretty clean. I suppose if you cut too fast it might come back too. Thanks a lot for the info! Jim