The vehicles are operating, but are running very slowly, Muni spokesman Paul Rose said.
Muni is setting up bus shuttles to supplement the light-rail vehicles that are delayed, Rose said.
The delays are expected to last throughout the morning commute, Rose said.
Because of heavy morning traffic and safety concerns, maintenance crews won't be able to fix the mechanical problems at the Embarcadero station until after 10 a.m., Rose said.
