Brake Fluid level in reservoir.

Brake Master Cylinder - General condition.

Proportioning/Safety Valve.

Brake Hydraulic Slave-Cylinders (at the wheel.)

Mechanical Brake Adjusters.

Brake Shoes/Pads (worn beyond limits.

Brake Drums - Beyond Wear Limits, Out-of-Round condition.

Leaks at Fittings or Bleed Valves.