Make it easy by swaping out the complete brake assembly and upgrading to self adjusting brakes at the same time. Four bolts, two wires and your done. To do one axle you'll need both right hand ( passenger side ) and left hand ( Driver side ) assemblies.
 
12in 5.2K-7K Left Hand ( Drivers Side ) Elec Self-Adj Drum Brake EB01-127
 
12" x 2" Left Hand ( Drivers Side ) electric complete brake assembly. For 5200lb, 6000lb and 7000lb Axles. These come standard with the larger magnet normally found only on 7000lb axles for increased braking power on the 5.2k and 6k axles. Mounts with 5 bolts (not included).  Brakes automatically adjust to deliver optimum performance and braking power. Reduce stopping distances 50 percent more than other brakes.  Save time and money.  Proper adjustment leads to better brake efficiency.
 
Uses 12" Hub/Drums. Bolts-7-5 and washers-38LW not included. 
 
• Fits standard 5200 lb, 6,000 lb-7,000 lb axles with a 5 bolt pattern on the mounting flange.
• Right Hand (passenger's side)
• Complete assembly ready to bolt on and wire
• For use with a 12" inside diameter drum
• The shoes are 2" wide
• Self-adjusting
• Mounting nuts included (5ea 38N)
 
To determine the size of the brake, you need 2 measurements.  The first is the diameter of the brake (D).  The second is the width of the shoe (W).  It is good to take note of how many mounting bolts the brake has.
 
These components have passed the CSA Standard CAN3-D313-M85 For Trailer Running Gear, a stringent standard mandated by the Government to assure brake effectiveness and structural integrity of the components.
ISO/TS 16949:2002 certified