Full services on one of London's busiest Tube lines will not be restored until Monday at the earliest, because of continuing safety fears.
Commuters arriving at Northern Line stations found them shut
The Northern Line shut on Wednesday night, after drivers walked out in a row over the emergency braking system.
The 660,000 commuters who use the line daily were faced with closed stations and long queues for replacement buses. It will remain suspended on Friday.
However, engineers think they have a solution but are still testing it out.
The problems began on 9 September, with the first emergency brakes failure.
Since then there have been four more brakes failures - the latest, on Wednesday, which led to the line's closure.
Drivers said back-up brakes are "vital" .
One told BBC London: "If you pass a red signal, it will stop the train. As a driver I put blind faith in the emergency braking system, without it I have no confidence I can ensure the passengers' safety."
London Underground (LU) is using emergency powers to oversee modifications of the trains by Tube Lines, the private consortium responsible for maintaining the Northern Line and its sub contractor Alstom.
LU's service director Howard Collins told BBC London they had put their best engineers in to work with the maintenance contractors.
"We have got involved with Tube Lines and Alstom and have found, we believe, the solution to this problem," he said.
The line carries more than 660,000 people every weekday
He said they would continuing running test trains until they were sure they had got to the root cause of the brakes failure.
The line will stay suspended throughout Thursday and Friday but a limited service will run at the weekend.
The Rail, Maritime and Transport (RMT) union welcomed assurances from LU that those who had refused to work would not face penalties.
London Assembly Liberal Democrat's transport spokesman Geoff Pope said Tube maintenance, which was privatised under the controversial PPP scheme should be brought back "in-house".
Conservative transport spokesman Roger Evans also felt the problems had descended into a "blame game" and said he despaired that the line would not be fully restored for days.
The RMT backed calls for the maintenance contracts to be ended and repairs to be bought back in-house.