Brittany Cartwright Doesn't Believe Rehab Changed Jax Taylor

Brittany Cartwright is putting her estranged husband, Jax Taylor, on blast ... claiming his stint in rehab didn't change him one bit.

The "Vanderpump Rules" alum opened up about her current relationship with Jax on Bravo’s "Hot Mic" podcast, where she said she saw little change in her ex -- despite his 30 days of treatment for his mental health.

As Brittany put it ... Jax didn't change "at all in those 30 days," promising her proof will play out on season 2 of "The Valley" -- which filmed over the summer.

She added ... "A lot of rage texting and stuff was still going on the entire time that he was in rehab. So, for me, I was just noticing like, this is just going to be constant."

According to Brittany, Jax would still call her names and "cuss [her] out" from while doing "therapy 7 hours a day" ... which is why she's confident the Bravo personality is "never gonna change."

This revelation is why Brittany has no regrets about her decision to file for divorce ... calling her separation a "very eye-opening" experience.

Brittany revealed in February that she and Jax had made the decision to take some time apart ... with BC moving out of their shared home.

Amid the separation, Jax, who shares son Cruz with Brittany, entered an inpatient treatment to work on his mental health.