MAKE DRUM BRAKES WORK BETTER

if you can't adjust your fronts anymore w/ cable and the lower adjustment take them all apart and clean them. then if they look good you can rotate the arm down. this will give you some adjustment back
 
You probably need to rebuild the rear caliper.
Here's what I did to my machine.

Take the rear caliper off and disassemle it to get to the brake piston. (The sliding piston has one of brake pads on it.)
The piston should slide freely inside the caliper, but it is probably corroded and filled with dirt. Clean the piston and make sure it doesn't have any big scratches that will keep it from sliding smoothly. Grease it up and put the caliper back together.

Another thing you may want to do is replace the rear brake cable. The stock cable is poorly designed because it goes up to the handlebars for your parking brake. When the cable starts to stick, the brakes work poorly. I bought a cable off eBay that eliminates the portion going to the bars. It works much nicer and came with the pins and adapters required to install it.

The rear brake on my machine works great now. Understand that a mechanical brake will never work as easily as hydraulic, but I can lock the rear tires.
 
I must have the only Blaster on the planet that the brakes work on!???
I've buried the front tires in the sand up to the lower control arms more than once! and I'm constantly killing the engine with the rear brake!, I've gotten use to letting off in time to roll start the engine so I can keep on going.
The rear caliper has an automatic adjuster so if it's not adjusted up it must be full of crap and corroded.
I never had any issues with the rear brake cables, but I did eliminate the upper cable when I put on the extended swing arm.