"High School Musical" was a slam dunk hit for Disney 20 years ago, but not for Bart Johnson -- who played Coach Bolton -- because he tells TMZ the movie f***** up his career at first!

It may be hard to believe, but Johnson tells us his acting career took a turn for the worse despite his skyrocketing fame as Zac Efron's on-screen dad and East High's head basketball coach in 'HSM.'

Check out our clip ... Bart tells TMZ he was "put out to pasture" for being a dad in a Disney movie, and it took a whole decade to get his career back on track.

Bart also tells us 'HSM' had a minor impact on his personal life, claiming his kids' elementary school barred him from dropping them off because his presence became too much of a distraction!

But Bart says he always stayed in the game and is now getting work again! In 2024, he landed the part of Aaron in Kevin Costner's "Yellowstone" and has a recurring role in Taylor Sheridan's "Landman."

"High School Musical" debuted 2 decades ago this week and it was a game changer for Disney Channel and many of the film's now big-name actors. As you know, Vanessa Hudgens, Ashley Tisdale and Zac all went on to do big things ... proving the film was the "Start of Something New."

During our interview, Bart also raves about how the 'HSM' franchise is being received by the next generation. And he teases a potential fourth installment after the third film premiered in 2008 ... even telling us he pitched his own idea. It's all in the clip.

Nothing has been picked up yet ... so we will have to "Stick to the Status Quo" and keep dreaming.