A new BART train that was on a test run broke down at the Lake Merritt Station in Oakland early Friday, causing delays that lasted into the peak morning commute hours, officials said.

The delays were resolved by about 9:15 a.m., according to BART spokesman Jim Allison, but not before dozens of trains ran late after the disabled train was stuck on the tracks.

“It was a four-car train made up of the new cars that were out for testing overnight,” Allison said.

BART is looking to expand its service with 1,081 new cars, 10 of which were delivered last year and are being tested before they operate with passengers. Another 775 cars are on order and scheudled to arrive over the next six years.

The train broke down shortly before 5 a.m., and trains were single-tracking through Lake Merritt station until shortly after 6 a.m., when the train was towed to a side track near the Bay Fair Station, Allison said. Even after the track was cleared, however, built-up traffic caused systemwide delays.

Just as those delays were clearing up, another problem occurred, this time in San Francisco, Allison said.

“What compounded the issue was that at 8:15, there was a train at Montgomery Station that had a door that wouldn’t close, and we actually had to take that train out of service.” he said.

“We were almost back on time and then that happened — it cost us another hour,” he said.

Filipa Ioannou is a San Francisco Chronicle staff writer. Email: fioannou@sfchronicle.com