Auto parts maker ArvinMeritor Inc. said Wednesday that it is moving its shock and strut manufacturing to Mexico, eliminating about 270 jobs at an Oklahoma plant. The plant is part of ArvinMeritor’s light vehicle aftermarket business — a unit the company has said it plans to sell. The company said that the outsourcing is necessary to keep the business competitive. The company said it will begin shifting operations to its Queretaro, Mexico, facility in September and conclude the move in November. The job cuts account for about 46 percent of the work force at the Chickasha, Okla. factory, which currently employs about 587 people, according to spokeswoman Krista McClure. The company said it will maintain the other operations — packaging, distribution, receiving, returns processing, design engineering and rod manufacturing. “It will continue to be the distribution center. Even the products that are being produced in Mexico are distributed out from Chickasa,” McClure said. Shares of ArvinMeritor slid 3 cents to close at $17.65 on the New York Stock Exchange.