The STM has pulled all 12 of its new Azur trains from service indefinitely following last Saturday evening's 10-hour shutdown.
The shutdown paralyzed service on the entire western end of the orange line, between the Lionel-Groulx and Côte-Vertu stations.
The transit authority says the shutdown was caused by a part of a metro train rubbing against the rails at the Du Collège metro station, damaging signaling equipment.
It suggests, however, that the problem might not be unique to the Azur trains — some of the older MR-73 had the same problem, though they suffered less damage.
The newer trains will be out of service until further notice — until the transit authority sorts out the problem.
The Azur trains, manufactured by the Bombardier-Alstom consortium, entered service last February, after years of delays. 52 of them are expected to be rolling on the metro's orange line by the end of 2018.