Metro has pulled 14 of its newest railcars out of service after discovering a wheel problem that could affect more than half the agency's fleet of rail vehicles.

In a Dec. 10 inspection, Metro discovered that wheels are separating from the spot where they should be affixed to the axle, said Metropolitan Transit Authority CEO Tom Lambert. The cars were recently delivered to Houston by CAF U.S.A., the American wing of Spain's Construcciones y Auxiliar de Ferrocarriles.

The wheel issue is the latest in a series of problems Metro has had with the company, starting in 2010 when a $900 million federal light rail grant was threatened over violations of "Buy America" rules. Subsequent issues included delays in delivering cars, overweight vehicles and faulty seals.

Metro also owns 37 Siemens railcars, purchased in 2004 and 2012.

Officials do not believe the wheel issues compromised the safety of riders or of Metro employees, Lambert said. The defect was discovered long before it could have led to a failure or derailment, officials said. The new cars have been phased into the fleet since January.

'Hugely disappointing'

Removing the 14 cars from service has not affected train operations or led to crowding on railcars, as ridership is typically lower during the holiday season, officials said. The full set of trains will be needed once ridership on the new Purple and Green Lines increases.

Metro board chairman Gilbert Garcia acknowledged that the transit agency's relationship with CAF U.S.A. has been problematical. A financial settlement is likely as part of a damage claim that commonly ends a lengthy purchasing process.

"We're just so far down the road with this car, we need to do everything we can to make this work," Garcia said. "But yeah, there is no way around it, this is hugely disappointing."

For now, Metro officials said they're focused on getting railcars running. CAF is cooperating, officials said; the company sent two engineers from Spain within two days of the problem being identified.

"They recognize the issue, and it appears they are owning up to it and they are really going out of the way to fix this," Garcia said.

CAF officials in Washington said they could not provide details about the problem or possible solutions until they consulted with engineers in Spain on Friday.

Engineers are inspecting every CAF railcar daily, Metro board member Jim Robinson said.

"If we find any separation, it's going to be parked," Robinson said.

Problems abound

Controversy has surrounded the CAF contract from the beginning. Metro nearly lost its federal funding commitment to help pay for the Green and Purple lines when the Federal Transit Administration said CAF's Spanish-built trains violated rules requiring that railcars be assembled in the United States.

That led CAF to shift more work to its Elmira, N.Y., plant, and Metro belatedly received the federal money.

In January 2014, Metro withheld a $12.8 million payment to CAF because delivery of a working car was six months behind schedule, largely because of delays in Elmira.

The initial railcar weighed roughly 9 percent more than the 100,300 pounds Metro's contract specified. Heavier cars lead to higher operating costs. The cars also had a problem passing a water pressure test because of a faulty seal.

CAF fixed the seal problem and acknowledged the weight issue. The company accelerated assembly by increasing staff and facilities at the New York plant.

Construction of Metro's Green and Purple light rail lines missed earlier deadlines, allowing for later delivery of the light rail cars without affecting operations.

Neither of Metro's two railcar orders from Siemens was plagued by the manufacturing problems that have cropped up with the CAF contract, officials said.

The Siemens vehicles had been built to an established design when Metro purchased them, while the CAF cars used a new design, officials said. Railcars identical to the Siemens models operating along tracks in Houston can be found in San Diego, Portland, Ore., and other U.S. cities.

Metro was CAF's first light rail car customer in the United States, although the company is a titan of European light rail construction. Design details, however, vary between European and American models, Robinson said.

Issues in other cities

Other CAF contracts in the U.S. have also experienced problems, famously the company's agreement with the Washington Metropolitan Area Transit Authority. Transit officials in the nation's capital reported numerous problems with the 192 railcars they purchased from CAF between 2001 and 2004 for $383 million.

Lambert said Metro has been aggressive about identifying problems, bringing them to CAF's attention and demanding solutions. Buses can last about 10 years, but well-built railcars can last three times as long.

"We are making sure we have a quality product," Lambert said of the CAF vehicles.