[Zope] Convert TextIndex to TextIndexNG

Hi, I would like to use the TextIndexNG Product instead of the normal TextIndex for SearchableText in portal_catalog. I deleted the existing SearchableText and added a TING with the name SearchableText. Now I think I click on reindex and all my object that were in the old Index can now be used with the TextIndexNG. But after reindexing for a while there are no objects in SearchableText. How can I make my old objects belong to the new index type? regards Lars