For so many years, Knicks head coaches had come, gone and not used Walt Frazier’s knowledge despite him being present on the planes, trains and buses. Frazier, to a man, was always surprised at the lukewarm interest.

In fact, Frazier, the Hall of Fame guard with the NBA’s fastest hands, had told confidants he didn’t understand why former Knicks president Phil Jackson barely talked to him during his failed three-year, three-month stint. Frazier came into the league with Jackson and they were roommates as rookies.

Knicks coach David Fizdale, a people person dedicated to connecting Knicks history to his current group, has broken down the Frazier barrier. While some past Knicks players have only known Frazier best as the broadcaster in the loud suits, the current crop of guards are getting to know Clyde.

On Tuesday, Frazier was invited to the Knicks practice facility in Tarrytown for lunch with Fizdale and president Steve Mills, after which he met with the guards and chatted.

“Clyde came to the gym the other day and spoke to our guards,’’ Fizdale said. “Steve invited him for lunch and I previously invited him to spend time together and watch film. I wanted to introduce him to all of them — the guards — to let them know he will be talking to them very soon.”

While Frazier has traveled with the club for MSG Network, he has never wanted to overstep his bounds with the coaching staff. He’s also quite busy with side businesses — running a successful restaurant, Clyde Frazier’s Wine and Dine, in Midtown and a bed and breakfast in St. Croix, where he owns a number of properties.

“No one defended like Clyde,’’ Fizdale said. “You’re seeing the kind of DNA I’m trying to create with the guards. If they can embody what Clyde brought to the game, we got something pretty good. They may not know everything he’s done, but know he’s a legend.”

That defensive hustle was shown in Brooklyn on Wednesday. The prime example was combo guard Ron Baker diving on the floor for a loose ball and then feeding ahead for a layup and stealing another ball at midcourt for a layup. Fizdale got animated on the sidelines for both plays.

Privately, Frazier has always wanted to share his knowledge with the Knicks players in a formal way. In June, Frazier, key cog on both Knicks title teams, signed a new Puma deal that created a new wave of NBA players joining the old-school sneaker company that the Hall of Famer pioneered.

On Monday in Washington, Fizdale invited Georgetown head coach Patrick Ewing into the Wizards downtown arena for the Knicks’ morning shootaround and he gave a speech ahead of their preseason opener. The Knicks are 2-0 in preseason.

Undrafted rookie SG Allonzo Trier will continue to have the green light as long as he puts up numbers — 38 points in 47 minutes — like he has through the first two preseason games. Fizdale has emphasized ball movement and players not holding onto the rock for more than a second without purpose.

“That rule is out the door for ‘Zo,’’ Fizdale said. “Some kids are just natural scorers. I’m smart enough to know when to stay out of the way.’’

Trier, who lit up Brooklyn for 25 points in 26 minutes, is signed to a two-way G League contract, meaning he can’t be on the Knicks for more than 45 days once the regular season begins. The club likely at some point will rip up the contract and sign him to a regular 15-man roster minimum deal.

“We’re giving out spots to guys who earn it,’’ Fizdale said. “He puts in a lot of time, maybe the most time, to be honest with you. The kid comes back on most nights.’’

Said Enes Kanter, “He’s the same way in practice — amazing motor.’’