If you have a hammer you can never be "out of whack"

I think the term comes from the so called hammer mechanics. People who think hitting something will fix it.

If you can't hit it really hard and bend it back, then it's "out of whack" or too far bent to whack back... thus out of whack!

(don't believe a word I said except about the hammer mechanics)

I also searched my OED dictionary and found nothing of interest or pertaining to origins. Just out of adjustment.

Although the flyrod is askew on the tredle will suffice for most of an explaination.