The STM is still investigating exactly what went wrong Saturday with an Azur train.
A preliminary report filed Wednesday offered no real new information about what caused the equipment breakdown that forced the shut down of the western section of the Orange line.
On Saturday part of an Azur train smashed into key equipment on the tracks near the Du College metro station.
The STM quickly determined that the electrical contact pad - the part of the train that touches the third rail - had managed to hit signalling equipment on the track.
Further inspection showed that many trains were showing signs of damage, but nothing quite as severe as the train that was forced to stop.
The STM has since conducted further tests involving placing cameras on the underside of a train.
"Our first observation last night showed nothing wrong with the tracks so now we have to look at the footage at very slow speed," said STM Chair Philippe Schnobb.
The STM is also investigating the possibility of debris on the tracks causing the damage.
Until the agency has a solution, the Azur trains will not return to service.
"The reason we pulled the Azur is not because there's a trouble with Azur but it's because we want to protect the Azur. It's a preventive measure," said Schnobb.
As a result of the missing 12 trains, service has been slightly reduced.
Meanwhile the damaged parts are being examined by engineers at Ecole Polytechnique de Montreal, and Mayor Denis Coderre wants a final report by the end of the week.
