Brake Issue

[MikeF]

2004 v6 LS. Recently started having an issue with the brakes. Affter sitting overnight (10-12 hrs) when I back the car out of the garage the brake pedal is very hard and almost no stopping power. After several pumps pedal feels normal and brakes work fine. Restof the day brakes work fine. Can go to work where car site for 8-10 hours and pedal and brakes work fine when it's time to go home. It only happens in the morning after sitting all night. Reservoir is full ans pads rotors are fine. Any thoughts?

 

[joegr]

That's odd. My best guesses would be:

1. Vacuum plumbing issue, little or no vacuum getting to the brake booster. However, I don't see how pumping the brakes would fix that.

2. Internal brake booster problem.

3. Master cylinder problem.

 

[M4rk]

Component Tests

Brake Booster

• Check the hydraulic brake system for leaks or insufficient fluid.
  
• With the transmission in NEUTRAL, stop the engine and apply the parking brake control. Apply the brake pedal several times to exhaust all vacuum in the system.
  
• Apply the brake pedal and hold it in the applied position. Start the engine. If the vacuum system is operating, the brake pedal tends to move downward under constant foot pressure.
  
• If downward movement of the brake pedal is felt, the brake booster is functioning. If no downward movement of the brake pedal is felt, install a new brake booster.
  
• Operate the engine a minimum of 10 seconds at fast idle. Stop the engine, and let the vehicle stand for 10 minutes. Then apply the brake pedal with approximately 89 N (20 lb) of force. The brake pedal feel should be the same as that noted with the engine operating. If the brake pedal feels hard (no power assist), install a new brake booster vacuum hose assembly and retest. If the brake pedal feels spongy, bleed the hydraulic system to remove air. Refer to Brake System Bleeding in this section.

My pedal is also firm after the car sits for some time. Brakes operate fine. Vacuum works as described in above in the 3rd point. I suspect I have a bad vacuum hose assembly, or check valve.

 

[msgtusmc]

Engine off. Pump brakes until hard pedal. Loosen right front caliper bleed valve, observe fluid flow. No flow. Do same left front. No flow, fluid topped off, cap off brake fluid container, might be bad brake line. Repeat procedure loosening brake line on each side. If fluid flow from brake lines, remove caliper, remove brake bleed valve, remove brake shoes, clean caliper surface of rust where brake shoes contact. Apply thin coat anti-seize on caliper for outside brake shoe. Re-install caliper, connect brake line, install cleaned or new brake bleeder valve. Bleed brakes. Top off fluid. Replace cap. Try this & above procedure again. If passes. Drive vehicle, test brakes.