Simply remove all the users/groups that are listed as readers or
authors. You should be able to do this via the MMC for SPS for each
workspace. For all folders that inherit the parent's permission set you
will not have to do anything. For all folders that do not inherit the
permissions from parent, you will need to go in and make  the same
changes.
Does this solve your issue?

If a dashboard  is only visible for Autors, also the Link to this
dashboard should be visible only for Autors.

I dont like to add each Autor to the permissions table, I like to do
like this: only users, which are definied as Autors, should have the
right to see the dashbord.

The Problem now: I have a dashbords called "autors", in which the
autors have administrative links. also readers can see the dashboard
and the links, but this links are only for the autors.

I cannot imagine, that the problem is only on my side.

Have you remove the account everyone with reader role on the folder Author
in the directory Portal of workspace?
Normally if you do this, reader cannot view the sub-dashboard author