It's always good to pull the rear drums and dump the dust out. If you have shop air, blow it out, but you will be covered with that shit. But it wil cake up if you don't clean it out ever time you chage the front brakes, and also like the other guy said, adjust them...
If you don't know how there is an art to adjusting drum brakes..
you can buy some special tools, but you can get away with using basic hand tools.
Some cars use a tool called a spoon that is used to slip into the back of the rear brake assembly to adjust the brakes. There are also spring pullers. You can buy a spray can of brake cleaner and also buy a bleeder kit.
you adust them with the weird screw nut thingy, until you can barely slip the drum on and off and if it scrapes a little bit when rotating the drum, affter putting it back on, back it off a couple clicks on the adjuster... if it's to tight you will burn up your rear brakes, they wil be too tight and alwasy be on. You have to find the exact point wqhen they are released and allow for expansion when they get hot. Rear drum brakes should last at least 3 front brake pad changes.