Why do we say something is out of whack? What's a whack?

Something that is "out of whack" means that it's illogical. A whack in this context would be logic.

before there was solid state there were tubes and "Air Capacitors" a multi gang fin tuner for radios. Whacking such a electronic unit would jolt dust from between the fin gangs and or realign filaments inside tubes that might have cooled wrong or have warmed up out of alignment of the hot filaments with the charge grids that acted as electron guides in the tubes.

According with Dictionary.com: "Out of whack" Informally means improperly ordered or balanced; not functioning correctly.

The following is an extract from "World Wide Worlds", that support the notion that "out of whack" means "out of order" or "broken":

There seems to have been a phrase "in fine whack" during that century, meaning that something was in good condition or excellent fettle. (It appears in a letter by John Hay, President Lincoln's amanuensis, dated August 1863, which describes the President: "The Tycoon is in fine whack. I have rarely seen him more serene and busy. He is managing this war, the draft, foreign relations, and planning a reconstruction of the Union, all at once".) It doesn't often turn up in writing, though, so there's some doubt how widespread it was.

To be out of whack would then have meant the opposite that something wasn't on top form or working well. It was first applied to people with ailments ('My back is out of whack'). In the early years of the twentieth century it started to refer to mechanisms. It might be that the sense was influenced by the idea that faulty mechanisms responded to a quick thwack.

For the complete article visit:
http://www.worldwidewords.org/qa/qa-out2.htm

Whack as a stand alone word means: to strike, to murder (slang), a sharp blow (or its sound), to masturbate (whack off), to attempt,
crazy, exhausted or under the influence (whack out).

Lots of meanings, uh?

It's pretty quack, yo!

(Like Freud, who was a whack quack)

When in doubt, ask The Word Detective:

La vida lopsided.

Dear Word Detective: I've used this phrase so many times I never pondered its origin, but now I'm curious. When something seems not to be quite right, I'll say, "It seems to be out of kilter." I know what I mean when I say it, but have no idea what "kilter" is. I'm assuming in some ancient Celtic or Germanic language it meant to be "level" or "plumb" or some such builders' vernacular. Am I way off base on this? -- Scott Jackson.

Dear Word Detective: Whence commeth "out of whack"? It can't related to "wacky," meaning "zany or strange," because then being out of it would be to operate normally. And where can I purchase additional supplies of whack in order to be prepared for future shortages? -- Whacking my brain, Martin Ornstein.

Greetings, and welcome to That Ain't Right Week, our annual celebration of all things out of whack, out of kilter, and just plain not the way they're supposed to be. As always, this column comes with our standard 30-day warranty, under which claims for defects may be filed day or night on any day not ending in the letter "y." And remember, your phone call is important to us, so we're keeping our number a secret.

Scott, your theory about "out of kilter," meaning "not in proper order or working condition; defective or malfunctioning," being derived from an ancient building term is entirely reasonable, but, unfortunately, unverifiable. We do know that "out of kilter" has a positive form, to be "in kilter," and that "kilter" first appeared in the 17th century in the English dialect form "kelter" (still used, largely in Britain) meaning "in good condition or health." But the trail is cold as to the antecedents of "kelter" and their possible meanings.

And actually, Martin, "wacky" may very well be related to "out of whack." When it first appeared in the 18th century, "whack" meant simply "to beat or strike vigorously," probably formed from the sound of such a blow. "Wacky" (or "whacky") may simply liken the eccentricities of a "wacko" to the results of a blow to the head. "Whack" as a noun became thieves' slang in the late 18th century for "share of the loot" (possibly in the same sense we use "cut" today) and later came to mean "agreement or bargain." By the late 19th century, "out of whack" had come to mean "out of proper order or alignment," possibly from a further development of "whack" meaning "agreement or expectation."

http://www.word-detective.com/102805.html#kilter%20whack

What we realy should be asking ourselves is how do you get into a whack?

I've heard the saying " out of Whack" and in some form of slang, it means out of order,

It refers to some whom has self fulfilled to numerous a time. I believe its old English ,Or is that wanker? oh well either way.

Back when electronics and other appliances were still in their primitive forms, people used to whack things to make them work right. Often times if you whacked a television that wasn't functioning, it would work again. So for this reason, if something was out of whack, it needed to be whacked

Hope this answers your question

I havent got the whackiest idea!! (",)
+4

A whack is terminology relevant to comedy.

Whacky, means someone is in tune with the crowd to get laughs.

Whacked, usually means someone's whackiness has come to an end- permanently. "I want Him Whacked!

And thus the term: "Out of whack" is a commentary meaning that they're not in tune with the crowd.

When he, she, or it are out of whack, you whack them, then they have enough whack to last a while. lol

The corrective action. (Slang)

Out of whack implies it needs to be wacked (again).