When the engine is running the brake pedal goes to the floor with no resistance

Good morning,

No to the booster. Even with a bad booster, you would still have a pedal.

A used master cylinder is a bad idea. It is from a junkyard and could be contaminated with dirt, debris and bad fluid. I would get another master cylinder and start from there.

I attached the brake bleeding procedure for you to follow. You need a pressure bleeder for this operation.

Roy

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2003 Chevy Truck TrailBlazer 4WD L6-4.2L VIN S
ABS Automated Bleed Procedure
Vehicle Brakes and Traction Control Hydraulic System Brake Bleeding Service and Repair Procedures ABS Automated Bleed Procedure
ABS AUTOMATED BLEED PROCEDURE
ABS Automated Bleed Procedure

Two - Person Procedure

Caution: Refer to Brake Fluid Effects on Paint and Electrical Components Notice in Cautions and Notices.

Caution: Refer to Brake Dust Caution in Cautions and Notices.

Important:
Use the two-person bleed procedure under the following conditions.
- Installing a new Electro-Hydraulic Control Unit (EHCU) or new Brake Pressure Modulator Valve (BPMV).
- Air is trapped in the valve body.
Do not drive the vehicle until the brake pedal feels firm.
Do not reuse brake fluid that is used during bleeding.
Use the vacuum, the pressure and the gravity bleeding procedures only for base brake bleeding.

1. Raise the vehicle in order to access the system bleed screws.
. Bleed the system at the right rear wheel first.
3. Install a clear hose on the bleed screw.
4. Immerse the opposite end of the hose into a container partially tilled with clean DOT 3 brake fluid.
5. Open the bleed screw 1/2 to 1 full turn.
6. Slowly depress the brake pedal. While the pedal is depressed to its full extent, tighten the bleed screw.
7. Release the brake pedal and wait 10-15 seconds for the master cylinder pistons to return to the home position.
8. Repeat the previous steps for the remaining wheels. The brake fluid which is present at each bleed screw should be clean and free of air.
9. This procedure may use more than a pint of fluid per wheel. Check the master cylinder fluid level every four to six strokes of the brake pedal in order to avoid running the system dry.
10. Press the brake pedal firmly and run the Scan Tool Automated Bleed Procedure. Release the brake pedal between each test.
11. Bleed all four wheels again using Steps 3-9. This will remove the remaining air from the brake system.
12. Evaluate the feel of the brake pedal before attempting to drive the vehicle.
13. Bleed the system as many times as necessary in order to obtain the appropriate feel of the pedal.

Not at all. You need basic brakes first for the ABS to work.

Roy

You are welcome.

Always glad to help.

Roy

A bad booster will not cause it to have any pressure.

Try using vice grips and clamp off the brake hoses to each wheel. Clamp all them off to start and see if you have a pedal.

If you do, then the issue is at one of the wheels. Release the vice grips one at a time unitl you lose the pedal. That is the wheel with the issue.

If you do not have a pedal, then you either have air n the system or a leak in one of the lines.

Roy

You are welcome.

Always glad to help.

Roy