Brake Assist Noise Inspection

WARNING: This page is about a different car, the 2002 GMC Safari and 2002 Chevrolet Astro. However, it is still accessible from the selected car via links, so may be relevant.

Install Brake Pedal Effort Gauge (J-28662) to brake pedal.
Start and allow engine to idle. Ensure that wheels are directed straight ahead.
Apply and maintain brakes with 25 lbs. (111 N) of force to brake pedal, as indicated on the brake pedal effort gauge. Observe for noises.
Quickly release brakes. Observe for noises.
If chatter and/or a vibration of the brake pedal was apparent during the brake system apply of 25 lbs. (111 N) of force, the power steering drive belt is probably slipping and would require replacement.
If any significant noise was apparent during the quick release of the brakes following the brake system apply of 25 lbs. (111 N) of force, there is likely a restriction in hydraulic brake booster power steering return hose and it would require replacement.

NOTE: Do not apply 100 lbs. (445 N) or more of force to brake pedal for more than 5 seconds at a time.

Apply brakes with 40 lbs. (178 N) of force to the brake pedal, as indicated on the brake pedal effort gauge, then gradually increase pedal effort up to 100 lbs. (445 N) of force for not more than 5 seconds at a time.
Observe for noises. Quickly release brakes. Observe for noises.
If a hiss noise was apparent and increased during the brake system increasing apply 40-100 lbs. (178-445 N) of force, the hydraulic brake booster assist system is operating normally from an audible standpoint.
If a clunk, chatter, and/or clicking noise was apparent during the quick release of the brakes following the brake system increasing apply 40-100 lbs. (178-445 N) of force, the hydraulic brake booster assist system is operating normally from an audible standpoint.