Replace brake booster, now brakes go to floor

Tiny
MARKHUG3555
  • MEMBER
  • 2003 CHEVROLET S-10
  • 4.3L
  • V6
  • 2WD
  • AUTOMATIC
  • 380,000 MILES
I had a hissing sound when I pressed the brakes and car idled rough. I replaced the Brake Power Booster without disconnecting any lines. Now my brakes go all the way to the floor and the brake lights come on.

My guess is the system needs to be bled, even though it was never opened.

Any other thoughts before I do this? Thanks.
Saturday, December 21st, 2019 AT 12:56 PM

5 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good afternoon,

Did you use a new one or used unit?

Did you remember the rod between the booster and the master cylinder?

I agree, if you did not open the lines, it should not need to be bled.

Roy
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Saturday, December 21st, 2019 AT 1:28 PM
Tiny
MARKHUG3555
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It was a new booster. There is no rod between booster and master cylinder. Just a short plunger. I took the master cylinder back off to make sure the new one had one.
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Saturday, December 21st, 2019 AT 1:33 PM
Tiny
ASEMASTER6371
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Good. Need to be sure it is there. That is the rod I was referring to.

Then the next step is to bleed the system.

Roy

ABS Automated Bleed Procedure

Two - Person Procedure

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.
2. 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 filled 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.
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Saturday, December 21st, 2019 AT 1:36 PM
Tiny
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  • 3 POSTS
Thanks. I'll run to town tomorrow and get some fresh fluid. I'll let you know how it went.
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Saturday, December 21st, 2019 AT 1:40 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
You are welcome.

Always glad to help.

Roy
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Saturday, December 21st, 2019 AT 1:42 PM

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