Lil Wayne Sues Birdman's Cash Money -- I Want Out!

Lil Wayne has made good on his promise to go after Cash Money ... because he's filed a lawsuit asking a judge to end his contract with Birdman's label.

According to the lawsuit, obtained by TMZ, Wayne says Birdman and company violated the deal by withholding tens of millions of dollars Cash Money owes him for his long-delayed album, "Tha Carter V."

Wayne claims because Cash Money is refusing to pay, he's entitled to walk.

But Lil Wayne wants more than just a declaration of freedom. He's suing for $51 MILLION.

And Wayne wants the judge to declare he's the joint copyright owner of all Young Money recordings ... which includes Drake, Nicki Minaj and several others.

Sources connected to Wayne tell TMZ ... if Birdman antes up then he can release "Tha Carter V," but only if Wayne gets paid. Wayne says he was supposed to get an $8 million advance when he began recording in December, 2013 and another 2M when he completed the album a year later, but so far he's gotten nothing.