Rasheed Wallace won’t be contributing to the Pistons’ cause anymore. He’s gone, off to the hated Boston Celtics.

Wallace will be missing when the Pistons gather for training camp this fall, but he won’t be missed.

The Pistons won’t have him anymore, but I challenge you to notice the difference.

Wallace has been AWOL from the Pistons for too long now. His signing with the Celtics just makes it official, is all.

Speaking of missing…

Once, Wallace was the missing piece. He was the final addition to the puzzle, when Pistons President Joe Dumars stole him from the Atlanta Hawks in February, 2004. His energy, outside shooting touch, and athleticism in the post was just what the doctor ordered. The Pistons, likely, don’t win the NBA Title that year without acquiring him.

Now, he’s leaving, and whether it’s because the puzzle has changed, or his piece has become deformed, it doesn’t matter. Rasheed Wallace is an ex-Piston and the only regret should be that it didn’t happen sooner.

Wallace was particularly missing last season, when the Pistons could have really used his participation in the wake of the Chauncey Billups/Allen Iverson swap and the Rip Hamilton pouting jag and eventual injury.

Not to mention to provide some veteran leadership, a lot of it gone to Denver with Chauncey.

A rookie head coach could really have used some help from his supposed leaders. A veteran dude like Wallace could have been indispensable.

But Sheed showed his true colors. He lied down on the Pistons, turning in one uninspired performance after the other.

It used to be that you could put up with Wallace’s antics, because his play was in the upper echelon of power forwards/centers in the league. The ill-timed technical fouls, the ejections, the loss of emotional control that would affect his game for several minutes — you could abide that, because Rasheed was good for 15 to 20 points and about 10 boards and a couple of three-point daggers every night.

But each year he was a Piston, his fuse got shorter and his production got smaller.

By last season, Wallace was a shell of the player he was when the Pistons traded for him.

It wasn’t just his age (he’ll be 35 in September) that made his numbers shrink, either. It was his attitude.

It won’t surprise me, not one bit, if Sheed goes to the Celtics and elevates his game. He’s probably at that “needs a change of scenery” part of his career. The Celtics are a better team than the Pistons, and are clearly championship caliber.

The Celtics, in fact, are a much better team than even the 2004 squad that Wallace joined in Detroit.

Maybe he needs to sniff a title to get interested again.

Rasheed Wallace, when he’s engaged both physically and mentally, plays basketball with a fury like few others I’ve covered and watched in my 30-plus years of observing the NBA. When he cares to be, Wallace can be a marvelous player — a bona fide game changer.

He just has rarely cared to be, in Detroit as of late.

Sheed’s mental breakdowns have been voluminous, but perhaps his most egregious example was in Game Five of the 2005 Finals against the Spurs, at the Palace.

The Pistons had drawn even in games, 2-2, and were in a dogfight at the end of Game Five. They managed a two-point lead in the final seconds. The Spurs inbounded the ball.

Wallace, for whatever reason, left his man, Robert Horry, to double-team Manu Ginobili in the corner, a senseless move. Ginobili recognized it right away and kicked the ball back to the unguarded Horry, who had murdered the Pistons in the fourth quarter with his deadeye shooting.

Horry calmly drained a game-winning triple, shoving the Spurs to a 3-2 lead. They won the series in seven games.

In my cleverness and incredulity, I wrote that Wallace left the wolf to guard the sheep.

A couple of years ago in the conference finals, they all but had to drag him kicking and screaming from the arena in Cleveland, after Wallace got ejected while his teammates were trying to force a seventh game.

I, for one, won’t miss Rasheed Wallace. Once, he was the fire and brimstone that the Pistons needed to win a title. That was then.

Wallace, by the end of his time with the Pistons, had denegrated into a disinterested, scowling malcontent. It used to be that Sheed saved his disdain for his opponents and the officials. By the end, even his own team wasn’t immune to his toxic behavior.

Now he’s gone, off to Boston, where the Celtics hope he can do for them what he did for the Pistons five years ago — to be that missing piece.

In Detroit, he was just missing.

No Sheed.