The transit agency serving Philadelphia and its suburbs is warning regional rail riders of possible major disruptions in the days and weeks ahead after the company had to take about one-third of regional rail cars out of service due to a structural problem.

The Southeastern Pennsylvania Transportation Authority said all 120 Silverliner V cars were taken out of service after workers noticed a "slight lean" on one of the cars and found a fractured beam in the suspension system. SEPTA immediately put a speed restriction on the Silverliner V cars and took them out of service Friday night. Only five of 100 cars inspected so far don't have fatigue cracks, officials said.

"We are good through the July 4th holiday," SEPTA General Manager Jeffrey Knueppel told reporters Sunday. "With one-third of our fleet out of service, however, Tuesday is the challenge — and, unfortunately, it will be rough on our railroad customers."

Knueppel said officials plan to run Tuesday's regional rail lines on a modified Saturday schedule developed for weather emergencies and adding additional service during rush hours, approximately every 30 minutes. The company is looking at equipment leases and service arrangements with New Jersey Transit and Amtrak, and increasing bus service.

"We ask for our riders' patience during this difficult time," Knueppel said. "The first days and weeks of this adjustment time should prove to be the hardest."

Knueppel said the cars are still under warranty, and manufacturer Hyundai-Rotem Corp. in South Korea is helping to locate and expedite materials for repair and replacement. The company is assembling engineers to determine whether welding can fix the problem or whether the beams will have to be replaced. The company eventually plans a full replacement program with a new design.

"Given the high number of cracked equalizer beams, even an interim fix will take considerable time," Knueppel said. "It is likely that car shortages will persist on the railroad at least through July and August."

SEPTA also plans to bolster service on the Market-Frankford, Broad Street, Norristown High-Speed line and Media-Sharon Hill trolley lines, and is working with the city and school district to increase parking along those lines, for example at nearby schools where students are out for the summer.

"It is likely that the trains at interior railroad stations — those closest to Center City — will prove difficult to get on due to overcrowding conditions in the morning," he said. "These service options may be especially appropriate for those regular railroad riders."

Knueppel said service related to the Democratic National Convention at the end of the month is expected to involve the Market-Frankford and Broad Street lines more than regional rail lines.

No such problems have occurred in 40-plus years on Silverliner IV cars, Knueppel said.

The Silverliner V cars were purchased for $274 million from Hyundai-Rotem Corp. in South Korea arrived between 2010 and 2013 after being shipped to South Philadelphia for final assembly. Their implementation was delayed several times, with the company in 2010 attributing the delays to late shipments, poor workmanship and management problems.