Four of them had been told on Monday they had failed in their applications to become one of six new corporate managers - posts created in the ongoing reorganisation of the council's political and management structures.
These included education director Tom Davies and housing director Christine Laird, who was only appointed earlier this year. The other four of the eight, including director of finance Keith Bray, had opted for voluntary redundancy.
One£70,000 corporate manager job will be advertised externally after the four existing service directors were judged not to be suitable following a two-day assessment by chief executive Byron Davies and external consultants.
The appointment of the five successful officers was approved by a panel of members chaired by lord mayor Russell Goodway. It is understood that panel members expressed considerable disquiet about both the lack of education expertise and the failure to fill all six corporate manager posts.
Hundreds of staff from all unions took part in a minute's silence at 5pm on Tuesday as the outgoing directors left the building.
Gareth Neale, leader of the council's Conservative group, said the treatment of the directors had been 'peremptory and unkind'.
'Staff will now be wondering how many second-tier officers are going to face the same treatment. We are succeeding in turning our own staff against us,' he said.
Cardiff's 14,000 employees were expected to hear yesterday the closely guarded secret of the council's new departmental structure. The 50 assistant directors of service will then be invited to apply for between 16 and 30 head of service posts and the corporate managers will be assigned areas of service responsibility.
Mr Goodway told LGC the reorganisation would have 'minimal impact on jobs below the senior level' and no impact on jobs on a salary below£28,000 a year.
The eight directors not appointed to corporate manager posts have been told to spend their three-month notice periods at home.
But the council said: 'Directors understand that, during the notice period, the council will, if necessary, call them into work on any specific matter.'