CHICAGO (CBS) — The Chicago Transit Authority has pulled 40 new rail cars from service because of a problem with a part on the so-called “5000-Series” model, which has been used on the Pink Line.

The cars were taken out of service Thursday night as a precaution, according to a news release provided by the city’s Transportation Department. Cars from the CTA’s existing fleet will replace the 40 cars while the CTA and the manufacturer “further study the issue,” the release said.

The parts in question are wheel-bearing housings on the train cars. Officials noted a “flaw in the quality of a casting used to create” them, according to the release. Replacements for those parts also came under scrutiny.

“This decision demonstrates an abundance of caution on our part as we work with Bombardier (the manufacturer) to address these issues,” said CTA President Forrest Claypool said in a written statement.

All inspection and related work will be paid for by Bombardier as part of the contract warranty.

CTA ordered the new-generation rail cars in 2006, and tested them in 2010 and 2011.  The cars went into full-time service on the Pink Line in November.  The new cars will replace CTA’s oldest rail cars, which are between 32 and 42 years old.