8:10 AM PT -- Brown's rant wasn't all talk ... he just met with team owner Art Rooney II and says they both agreed it's time to part ways.

"Had a great meeting with Mr.Rooney today we discussed a lot of things and we cleared the air on several issues!

"We both agreed that it is time to move on but I'll always have appreciation and gratitude towards the Rooney family and @steelers organization!"

"If your team got guaranteed money ... tell 'em call me" -- Antonio Brown (from his elliptical machine Monday night).

"I ain't got time to waste," AB added ... "I got FIVE KIDS. Ya heard!?"

It was all part of a 9 MINUTE rant on Instagram, which featured Brown working out like a maniac, sweating his face off ... and trying to convince NFL teams to sign his ass.

"This is not a game people. This is not for show. This is not to be cool. This is really to inspire you that no one can determine your destination but you."

"I'm bringing high heat, coach! I'm gonna be relentless this year. If your team got guaranteed money, they wanna get to know me and work with me? Tell 'em call me!"

By the way ... Brown is already in the middle of a huge, 4-year, $68 million contract with $19 million guaranteed. Unclear exactly what he's looking for in a new deal.

As we previously reported, Brown has been talking with Jerry Rice and REALLY wants to end up in San Francisco next season.

But, as NFL.com pointed out ... since Brown is still technically under contract with the Steelers, any team that contacts him directly right now would be "tampering."

Brown doesn't seem to care about that -- he wants a new deal. And, a new nickname, saying he's over being called "A.B." and wants to switch to something sassier... "Mr. Big Chest."