2010 E350 4matic rear caliper bolt
 

can someone tell me what type /size bolt holds the rear caliper on to change the rear pads. It looks like a torn bolt. if so what size?

It is not a torx. It is a hex bolt. Sorry I don't remember the size off the top of my head. Just reach around there with a few sizes and stick them inside the rubber boot into the bolt head until you find the right size. I know you are kind of working blind since it faces away.

my description of a hex bolt is probably confusing. It is not a hex "head" bolt, but rather a bolt that uses a hex wrench or Allen to remove. Like a torx

If I remember correctly it is a cap screw with 8 mm Allen head but I'm not 100% sure. Could be 10 mm.