No brakes

101GMBLR

MEMBER
2005 CHEVROLET SILVERADO
4.8L
V8
4WD
AUTOMATIC
195,000 MILES

My truck pedal is firm until the vehicle is started.I replaced front pads, short hoses, calipers, wheel speed sensors and rotors, rear wheel cylinders, shoes and drums. Manually bleed rr, lr, rf, of in that order at least 5 times, no air! Had a bad master bench bled new master with hoses left set overnight checked next day no air. Installed a new booster old one full of fluid, then new master pumped pedal a few times with hoses still attached. No air!Unhooked hoses and installed the lines bled at connections a few times no air. Hooked up scan tool ran auto bleed 3, 4 times. Great pedal until started straight to floor cannot pump up till vehicle is shut off. Stumped or did I get a bad master or is something wrong with ABS? Any help much appreciated. Thank you

3 Replies

JACOBANDNICKOLAS

MECHANIC
109,709 POSTS

Is this the procedure you followed with the scan tool? (see below) If it is, there is no air in the system, and you have brake pressure at each wheel when you manually bleed them, I suspect you got a bad master cylinder.

Take a look through this link:
https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

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Here are the automated bleed procedure for the ABS. Let me know if this is what was done.

Important: This procedure may be performed on all vehicles EXCEPT those equipped with option code JL4, Vehicle Stability Enhancement System (VSES).

Important: The base hydraulic brake system must be bled before performing this automated bleeding procedure. If you have not yet performed the base hydraulic brake system bleeding procedure, refer to Hydraulic Brake System Bleeding (Manual) Hydraulic Brake System Bleeding (Pressure) in Hydraulic Brakes before proceeding.

1. Install a scan tool to the vehicle.
2. Start the engine and allow the engine to idle.
3. Depress the brake pedal firmly and maintain steady pressure on the pedal.
4. Using the scan tool, begin the automated bleed procedure.
5. Follow the instructions on the scan tool to complete the automated bleed procedure. Release the brake pedal between each test sequence.
6. Turn the ignition OFF.
7. Remove the scan tool from the vehicle.
8. Fill the brake master cylinder reservoir to the maximum-fill level with Delco Supreme 11 GM P/N 12377967 (Canadian P/N 992667) or equivalent DOT-3 brake fluid from a clean, sealed brake fluid container.
9. Bleed the hydraulic brake system.
10. With the ignition OFF, apply the brakes 3 - 5 times, or until the brake pedal becomes firm, in order to deplete the brake booster power reserve.
11. Slowly depress and release the brake pedal. Observe the feel of the brake pedal.
12. If the brake pedal feels spongy, repeat the automated bleeding procedure. If the brake pedal still feels spongy after repeating the automated bleeding procedure inspect the brake system for external leaks.
13. Turn the ignition key ON, with the engine OFF; check to see if the brake system warning lamp remains illuminated.
14. If the brake system warning lamp remains illuminated, DO NOT allow the vehicle to be driven until it is diagnosed and repaired.
15. Drive the vehicle to exceed 13 kph (8 mph) to allow ABS initialization to occur. Observe brake pedal feel.
16. If the brake pedal feels spongy, repeat the automated bleeding procedure until a firm brake pedal is obtained.
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Let me know.
Joe