The multi-million pound Midland Metro extension has been delayed for a third time because of problems with the new track.
The final section from Bull Street to Grand Central Station was due to be open to the public this weekend, after being put back twice before.
This time it is because safety testing of the trams on the new lines found the rails are not perfectly level.
Centro’s Midland Metro programme director Phil Hewitt said:
A Midland Metro family fun day at Martineau Place, near the new stop in Corporation Street, has also been cancelled on May 22.
The multi-million pound new fleet of trams began being tested on the final section of line in April, but only now has it been revealed that these tests have identified problems.
The Spanish manufacturer CAF is now analysing the data and then alterations to the lines will have to be made.
- Watch again: Midland Metro show off £40m trams to public
A total of £128 million has been spent buying 21 Urbos 3 trams, upgrading the tram depot in Wednesbury, and on the extension itself since 2012.
It promises to boost the West Midlands economy by more than £50 million a year and create 1,300 new jobs when complete, and bring more than three million people a year directly into Birmingham's main shopping district.