Just bought 2018 CPO GLS450. Rear brake pads only contact 50% of rotor surface. Dealer says is OK. How could this be, brake friction is reduced by 50%

 

Doesn't look right. Please post a photo of the pad.

 

here is the pic

 

Most certainly an issue with the pads themselves or not likely but an issue with the caliper only being pushed out on one side. Either or its an issue that shoul dbe looked at. I do brake service myself for years on all of my cars and I have seen once that a pad was just broken partially and only what is left is contacting the rotor. Without seeing the pad itself its hard to determine... Best to get it checked and its not normal as the dealership may mention,

 

Thanks!!!!

 

Looks like it has been sitting for a while and the rotor rusted. Take out and do some repeated quick stops from speed and look again. It may be nothing but if it still looks like that after the test stops there is something wrong with the pad or caliper.

 

The photos show the rotor.

Please post a photo of the pad. Agree that something is wrong with either the pad or the caliper. How many miles are on the vehicle?