Have 2005 trailblazer & had dard black dust collect around out-side of passenger side rear wheel and behind when I washed car. Could this be caused from the brakes? The tires are new and just added last week.
Yes, that could be brake dust and if it is, likely one or both of your rear calipers (I think this has rear disk brakes) is dragging and wearing out your brake pads.
This is especially likely if your gas mileage has been poor lately. Have your brakes checked ASAP. On a vehicle this old, with Delphi brake hoses, change the brake hoses as they’ve likely failed, or will soon.
Many Thanks & will have checked.
1 Like
If one wheel has more dust than the other, it’s almost a sure sign that one is dragging. The TB gets relatively lousy mileage so you may not be able to tell from that 
It is rear disc and checking them is fairly easy and straightforward. Caliper sliders are usual suspects. I’ve had 3 TBs so far, an '03, '05 and currently an '08. Haven’t experienced a bad hose yet but certainly another possibility especially if everything else checks out.
One thing you should check that these are notorious for- brake line corrosion at the left tower. They used a bogus IMO mounting and isolation scheme and they ALWAYS rot out there prematurely. I now remove that rubber isolator as soon as I get the vehicle and there is always signs of corrosion setting in there. Just ty-wrap the lines to prevent them from vibrating. There is another similar mount down by the steering rack for the brake a power steering lines. Same thing.