SEPTA has pulled 18 of its repaired Silverliner V railcars from service after a new defect was discovered over the weekend.

The transit agency said in a statement that a Saturday inspection by SEPTA and manufacturer Hyundai Rotem found a "clearance issue" that led to "minimal, occasional contact between old and new components."

The agency was forced to pull 120 Silverliner V cars – about a third of the Regional Rail fleet – from service in July due to a structural defect. The pulled cars have caused crowding, delays and reduced service throughout the summer.

Some of the repaired cars started returning to service at the beginning of September as SEPTA began to phase the sidelined cars back in.

After the new problem was discovered, Hyundai Rotem made a design change and cars with that modification will return to service this week, SEPTA said.

The agency has said it expects full service to resume in October. That plan remains on track, SEPTA said Monday.

SEPTA has been leasing cars from other transit agencies in an effort to augment its capacity in the meantime. All of the pulled Silverliner V cars should be back in place by mid-November.

"SEPTA is committed to making sure the repair process is done correctly to ensure a long-lasting life," Jeffrey Knueppel, SEPTA's general manager, said in a statement. "This is why we are conducting thorough tests and inspections, such as the one on Saturday that revealed this problem."

The initial problems were caused by fatigue cracks that formed in a key weight-bearing beam. SEPTA officials have blamed that problem on improper welding and a poor design.