DETROIT — United Auto Workers leaders have approved a proposed contract with General Motors Co. that promises raises, improvements in health care and a hefty signing bonus.

Leaders from GM’s 63 U.S. facilities met in Detroit to discuss and vote on the agreement Wednesday. Now it must be ratified by GM’s U.S. hourly workers. The four-year contract covers 52,600 GM factory workers.

Like a previous contract ratified by Fiat Chrysler workers, GM’s agreement would eliminate a two-tier wage system over eight years. GM now pays recent hires around $15.78 per hour. Under the new agreement, workers with four or more years of experience will make the top $29 hourly wage within four years; workers with less experience would make between $22.50 and $28 in four years and top wages in eight years.

UAW President Dennis Williams had promised – and won – richer benefits from GM, which is a bigger and wealthier company than Fiat. GM reported last week that it earned $1.36 billion in the third quarter. FCA lost $339 million during the quarter because of big recall costs.

Williams said lower-tier workers – who make up 20 percent of GM’s hourly workforce – will now be eligible for traditional health care benefits. Both tiers of workers would get an $8,000 signing bonus if they ratify the contract.

GM’s proposed contract also offers $60,000 for up to 4,000 eligible employees who agree to retire next spring. Williams said that is meant as a reward to longtime workers who stuck with the company and gave up wages and benefits during its 2009 bankruptcy.

The UAW and GM reached the proposed agreement Sunday night just before a deadline the union had set to strike.