Final answer:
Hard spots on a brake drum can lead to brake noise, vibrations, pulsation during braking, uneven brake wear, and decreased braking performance.
Step-by-step explanation:
Hard spots on a brake drum can cause various issues in the braking system of a vehicle. These hard spots are often a result of excessive heat and brake shoe contact, which causes localized hardening or distortion on the surface area of the brake drum. This can lead to brake noise, vibrations, and a sensation of pulsation when the brakes are applied. In some cases, they may also lead to uneven brake wear or decreased braking performance due to the loss of a smooth and consistent contact surface between the brake drum and brake shoes.