Brake bleed problems?

Tiny
DOOB
  • MEMBER
  • 2003 GMC SONOMA
  • 4.3L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 140,000 MILES
New master cylinder. I have bled with air comp assist just get little bits of fluid not a solid column of fluid. Also did auto bleed with scanner. Nothing! Prob fans proportioning valve. But don’t what to do with that.
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Friday, February 5th, 2021 AT 3:27 PM

37 Replies

Tiny
KASEKENNY1
  • EXPERT
Just to be clear, you replaced the master cylinder and now you cannot get brake fluid to the rear? If this is the case, did you bench bleed the master? If not we should do that now and just start fresh.

You can do it on the vehicle, just take the lines off and get a bench bleed kit from a parts store that basically just routes the fluid back to the reservoir. They should be clear tubes so that you can see it is a solid stream coming out of each chamber.

Here is a guide that will help with this:

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

There is a chance that you either got a faulty master or if it wasn't bench bled then it could have damaged the walls of the chambers and now it is not pushing fluid.

So basically we need to start at the beginning of the system and make sure you have no air. Then I would open the bleeders on the rear wheels and let them gravity bleed for a few hours. You should then get a steady drip then close them off and bleed them with the air bleeder that you used before.

Let's do this and go from there. Thanks
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Saturday, February 6th, 2021 AT 5:23 PM
Tiny
DOOB
  • MEMBER
Thank you. I will do that and get back to you.
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Saturday, February 6th, 2021 AT 9:57 PM
Tiny
ASEMASTER6371
  • EXPERT
Good afternoon,

If you have ABS, there is an automated process to bleed the ABS module. If you have air in the system, this must be done.

I posted it below for you along with the procedure for bench bleeding the master cylinder.

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

Roy

Master Cylinder Bench Bleeding

Notice: When adding fluid to the brake master cylinder reservoir, use only Delco Supreme 11, GM P/N 12377967 (Canadian P/N 992667), or equivalent DOT-3 brake fluid from a clean, sealed brake fluid container. The use of any type of fluid other than the recommended type of brake fluid, may cause contamination which could result in damage to the internal rubber seals and/or rubber linings of hydraulic brake system components.

1. Secure the mounting flange of the brake master cylinder in a bench vise so that the rear of the primary piston is accessible.

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2. Remove the master cylinder reservoir cap and diaphragm.
3. Install suitable fittings to the master cylinder ports that match the type of flare seat required and also provide for hose attachment.
4. Install transparent hoses to the fittings installed to the master cylinder ports, then route the hoses into the master cylinder reservoir.
5. Fill the master cylinder reservoir to at least the half-way point 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.
6. Ensure that the ends of the transparent hoses running into the master cylinder reservoir are fully submerged in the brake fluid.
7. Using a smooth, round-ended tool, depress and release the primary piston as far as it will travel, a depth of about 25 mm (1 lbs.), several times. Observe the flow of fluid coming from the ports.
As air is bled from the primary and secondary pistons, the effort required to depress the primary piston will increase and the amount of travel will decrease.
8. Continue to depress and release the primary piston until fluid flows freely from the ports with no evidence of air bubbles.
9. Remove the transparent hoses from the master cylinder reservoir.
10. Install the master cylinder reservoir cap and diaphragm.
11. Remove the fittings with the transparent hoses from the master cylinder ports. Wrap the master cylinder with a clean shop cloth to prevent brake fluid spills.
12. Remove the master cylinder from the vise.

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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Sunday, February 7th, 2021 AT 9:45 AM
Tiny
DOOB
  • MEMBER
Okay Ken, I bled master system while still on truck using hose kit. Am now 4 hours into gravity bleed and no fluid has came from rear bleeder screws.
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Sunday, February 7th, 2021 AT 7:05 PM
Tiny
ASEMASTER6371
  • EXPERT
Did you do the automated bleed with a scan tool? Without doing this, you cannot get the air out of the ABS.

Roy
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Sunday, February 7th, 2021 AT 7:07 PM
Tiny
DOOB
  • MEMBER
I was trying to gravity bleed the rear. But should I do an auto bleed? Just close rear bleeders and do the auto bleed now?
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Sunday, February 7th, 2021 AT 7:17 PM
Tiny
ASEMASTER6371
  • EXPERT
Gravity will not do it.

Yes, do the auto bleed and see if you get fluid to the rear when the air is gone.

Roy
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Sunday, February 7th, 2021 AT 7:18 PM
Tiny
DOOB
  • MEMBER
Okay, will do.
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Sunday, February 7th, 2021 AT 7:19 PM
Tiny
ASEMASTER6371
  • EXPERT
Keep us updated.

Roy
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Sunday, February 7th, 2021 AT 7:20 PM
Tiny
DOOB
  • MEMBER
Well did auto bleed. Still no fluid yet. I opened up rear pass bleeder Maybe will gravity ble.
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Sunday, February 7th, 2021 AT 8:13 PM
Tiny
DOOB
  • MEMBER
Maybe will gravity bleed overbite.
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Sunday, February 7th, 2021 AT 8:14 PM
Tiny
DOOB
  • MEMBER
Maybe proportioning valve outta whack! Frustrating
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Sunday, February 7th, 2021 AT 8:26 PM
Tiny
ASEMASTER6371
  • EXPERT
Do you have ABS?

If you do, there is no proportioning valve. If you do not, then yes, it could be.

What kind of scan tool did you use for the automated bleed sequence?

Roy
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Monday, February 8th, 2021 AT 1:47 AM
Tiny
DOOB
  • MEMBER
Angel 610 elite scan tool. There is ABS and there is a proportioning or combination valve between master cylinder and brake lines. Respectfully
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Monday, February 8th, 2021 AT 1:45 PM
Tiny
ASEMASTER6371
  • EXPERT
When you push the pedal down, do you have pressure at the outlet lines of the master cylinder?

Roy
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Monday, February 8th, 2021 AT 1:57 PM
Tiny
DOOB
  • MEMBER
Feels like it with motor off.
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Monday, February 8th, 2021 AT 2:12 PM
Tiny
DOOB
  • MEMBER
With engine on it just goes to floor.
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Monday, February 8th, 2021 AT 2:13 PM
Tiny
DOOB
  • MEMBER
Why is this GMC so difficult? Never had this much abuse!
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Monday, February 8th, 2021 AT 2:14 PM
Tiny
ASEMASTER6371
  • EXPERT
You need to crack open the lines at the master one at a time. Then have someone push the pedal and see if fluid comes out. Checking to see if the master is producing pressure.

Roy
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Monday, February 8th, 2021 AT 2:18 PM
Tiny
DOOB
  • MEMBER
Yes, will do.
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Monday, February 8th, 2021 AT 2:20 PM

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