DETROIT (Reuters) - Chrysler Group LLC's success in increasing auto sales this year will cause four of its North American assembly plants to forego the normal two-week summer shutdown this year, the company said on Wednesday.

Those plants are the Jefferson north plant in Detroit that makes the Jeep Grand Cherokee, the Belvidere plant in Illinois that makes the new Dodge Dart, the Toluca plant in Mexico that makes the Dodge Journey, and the Toledo Supplier Park in Ohio that supports the Jeep Wrangler built at the nearby Toledo North Assembly plant.

Two other plants will take one week off rather than the normal two, Chrysler said.

Taking a single-week break this summer will be the Sterling Heights Assembly Plant near Detroit that makes the Chrysler 200, and the Saltillo plant in Mexico that makes the RAM trucks.

Sterling Heights will shut in the week starting June 25 and the Saltillo plant will shut in the week starting July 16.

Other plants will have their normal two-week shutdown, Chrysler said.

Chrysler's auto sales jumped 33 percent in the first quarter, to 523,000 vehicles.

(Reporting By Bernie Woodall; Editing by Gerald E. McCormick)