Engineers struggling to fix a fault that has effectively shut one of London Underground's busiest lines think they have solved the problem.
Travellers have been walking or taking the bus instead of the Tube
People served by the Northern Line face a third day of travel misery as the line remains suspended on Saturday.
The line was first suspended on Wednesday night after drivers walked out in a row over the emergency brakes.
But Tube Lines said it was confident a solution had been found and the line would reopen "in a matter of days".
In the meantime, travellers are being advised to use buses laid on to provide replacement services.
'Working around the clock'
Drivers are refusing to work on the Northern Line because of a series of failures of the emergency brakes, which stop the train if it runs through a red signal.
Stephen Peat, from Tube Lines, the private consortium responsible for maintaining the line, told BBC London: "This is a 10-year-old design problem we have inherited.
"Tube Lines engineers, Alstom engineers and London Underground's engineers have been working around the clock to try to solve this.
"They have come up with a modification to the switch... it seems to be working very well. The engineers are very confident this should eradicate the kind of problem we have been having."
Ten trains have already had the modification fitted and Mr Peat said engineers would be working "through the night" at the Golders Green depot to modify the rest of the 84-strong fleet.
London Underground (LU) used emergency powers to oversee modifications of the trains by Tube Lines and its sub contractor Alstom.
The problems on the line have prompted calls to bring Tube maintenance back "in house" - it was privatised under the controversial PPP scheme two years ago.