i have an all wheel disc model and i cant seem to figure out how to re-tension the wire running to the rear calipers, if theres a diy please point me there.

 

the tensioner has no more room left in it... so i was wondering how thick are the new shoes?

 

They could indeed be worn out.
There is also a Star type Brake adjuster (like on the Drum type Brakes) for the Parking Brake shoes that is accessed by way of a hole in the rear Hub.

This is a comment for anyone reading this: If you plan to keep your car and do your own repair work save yourself time and money and spend th $27 ($19.99+$7 shipping) dollars to get the Factor Service Manual CD from the Mercedes Classic Center.