Dodgers’ Yasmani Grandal is looking for the right stuff

Dodgers hitting coach Mark McGwire confesses he doesn’t know much about switch-hitting. So he shrugs his shoulders and admits he has no explanation for catcher Yasmani Grandal’s performance at the plate this season.

Grandal entered Tuesday’s game against the Washington Nationals hitting .350 against left-handers, second on the team to Enrique Hernandez. But just one of those hits has gone for extra bases.

Step across the plate, however, and Grandal becomes a slugger. All 15 of his home runs and 42 of his 44 runs batted in have come swinging left-handed. Among Dodgers, only Adrian Gonzalez has a higher slugging percentage against right-handers.

But Grandal, who had two walks and scored a run as a left-handed hitter Tuesday, is hitting just .277 from that side, 74 points below his average as a right-handed batter.

“It used to be the other way around,” said Grandal, who hit five of his first nine big league homers as a right-handed hitter.

That changed after Grandal had season-ending reconstructive surgery on his right knee midway through his second big league year, robbing him of his power.

“For me, being a guy who is used to just sitting back on that leg and turning on it, it becomes kind of difficult,” said Grandal, who has three doubles and eight RBIs right-handed since the surgery.

“It’s just a comfort level,” continues Grandal, who writes, brushes his teeth and does virtually everything but throw left-handed. “Even thought my knee is perfectly fine, it’s one of those things were you think about it and you’re used to making a certain move. Or when you do it, even though it’s the right move, sometimes it’s like I don’t want to hurt it again.”

Grandal also said platooning with A.J. Ellis, who gets most of the starts behind the plate against left-handers, has made it tough to get a rhythm going as a right-handed hitter. He’s had just 40 at-bats from that side this season.

And that’s something McGwire, a right-handed slugger in his playing days, does understand.

“The more he plays, if he gets his opportunities, you’ll see more home runs,” the coach said of the catcher. “To me, he’s fine right-handed.”

Kendrick update

Dodgers Manager Don Mattingly said Howie Kendrick’s left hamstring problem was rated between a Grade 1 and Grade 2 strain, on the bottom end of the severity scale. But he still anticipates Kendrick will be out until early to mid-September.

“Any time you say hamstring, you can assume, for me, bare minimum of three weeks,” Mattingly said. “I’m sure it will be more than that.”

Kendrick, who hurt the hamstring beating out an infield hit Sunday and went on the disabled list Monday, was sidelined twice during the 2008 season with strains to the same hamstring. He had an injection of platelet-rich plasma in his leg Monday in an effort to speed up the healing process.

Bullpen moves

The Dodgers placed struggling reliever Joel Peralta on the 15-day disabled list with a neck strain and recalled right-hander Yimi Garcia from triple-A Oklahoma City.

Peralta went on the DL with a similar problem in April and said he was days away from season-ending surgery before being cleared to pitch again in June. But Tuesday’s move comes following a rough trip for Peralta, who gave up game-changing home runs in both Philadelphia and Pittsburgh.

He made appearances in four games on the trip, giving up runs in three of them. For the season he has a 5.40 earned-run average in 25 games.

Garcia compiled a 3-2 record and a 3.99 ERA in 41 appearances during two previous stints with the Dodgers and was thrown right back into the mix Tuesday, coming on in the seventh to pitch two of scoreless innings.

More bullpen changes may be coming. Right-hander Chris Hatcher is eligible to be activated from the 60-day DL this weekend and Mattingly said he could join the team shortly afterward.

kevin.baxter@latimes.com

Twitter: @kbaxter11