Mazda RX-8 Workshop Manual page 1116

Generator brush length
Standard: 18.5 mm {0.73 in}
Minimum: 5.0 mm {0.2 in}
Brush spring
1. Measure the force of the brush spring using a spring pressure gauge.
2. Read the spring pressure gauge at the brush tip projection of 2 mm {0.079 in}.
Replace the brush spring if necessary.
Generator brush spring force
Standard: 4.8—6.0 N {0.49—0.61 kgf, 1.08—1.34 lbf}
Minimum: 2.16 N {0.22 kgf, 0.49 lbf}
Rectifier
1. Inspect for continuity of the diodes using a tester.