The STM will release more details Wednesday about the problems with the Azur trains that led to the shutdown of the Orange metro line on Saturday.

Officials with the STM admitted Tuesday that they knew in December of problems with the new Bombardier-Alstom trains, but did not expect anything like the damage caused this past weekend.

On Saturday the Orange line was shut down in mid-afternoon after signalling equipment at track level was badly damaged at the Du College station.

An electrical contact pad on an Azur car is to blame, and subsequent inspections showed damage on multiple trains. It convinced the STM to yank all Azur trains on Saturday and they have yet to be returned to service.

Opposition councillors want to know why, if the STM knew of a problem, the Azur trains were allowed to run.

"I think we're just starting to hear more about the story, about what exactly happened, and for us an important part was what was the decision-making process," said Projet Montreal leader Valerie Plante.

She wanted to know why officials waited "almost three weeks more before deciding to take the Azur trains out of service."

Mayor Denis Coderre is also upset with the problems caused on Saturday, and has pressed the STM for a report as soon as possible.

A dozen Azur trains were in service, with 40 more scheduled to be delivered by the end of 2018.