How do I bleed the brakes?

Tiny
RACHELMART19
  • MEMBER
  • 2003 CHEVROLET TAHOE
  • V8
  • 4WD
  • AUTOMATIC
  • 102,000 MILES
My brake fluid/system was ruined due to a faulty resevoir cap and condensation build up. The brake fluid was drained yet the rear fluid would not drain, since then the master cylinder(refurb) has been replaced yet the brake fluid is still not reaching the rear. I've done some research and I've been told it is the air lock in the proportion valve. Does that sound right and what is that? How would you replace? Also the resevoir had a green build up around it it has since been cleaned- Do you recommended replacing that altogether?
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Monday, January 12th, 2009 AT 2:29 PM

11 Replies

Tiny
JAMES W.
  • MEMBER
As long as the reservoir is clean and the cap fits well, I wouldn't worry about it. The proportioning valve won't block the fluid flow to the rear brakes. It meters the fluid between the front and rear brakes. If for some reason the front or rear brakes take more fluid than the metered amount because of a bypassing master cylinder, or a broken hose or line, the valves goes out of it's preset range and triggers the "brake" light on the dash. Air in the brake system will have the same effect. Most times you can't pump the brake pedal fast enough to force out the air. It keeps moving up in the lines. I would recommend taking the truck in and having the system "pressure bled". This moves the fluid through the brake system fast enough to remove the air. You may find you have a problem with the master cylinder caused by the contamination, but you won't be able to tell until the air is out. Here is a video and guide below to help you bleed the brake system correctly.

https://youtu.be/w7gUsj2us0U

and

https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

and

https://youtu.be/WDxvEQrMkBg

Please run down these guides and report back.
Hope this helps.
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Tuesday, January 13th, 2009 AT 2:56 PM
Tiny
JEFF BLANKENSHIP
  • MEMBER
  • 1999 CHEVROLET TAHOE
  • 4.7L
  • V8
  • 4WD
  • 273,000 MILES
Replaced front rotors, brake lines, pads, speed sensors and bed to the usual procedure of any other car. Rear brakes not getting fluid from the rear brake line at the master cylinder. Replaced pump and computer with that from a scrap yard. Same thing exists. No rear brakes. Monroe brakes and mufflers do not know how to fix this
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Tuesday, March 16th, 2021 AT 10:12 AM (Merged)
Tiny
STEVE W.
  • EXPERT
Did they put a scan tool on it and run the ABS bleeding procedure? When the ABS unit thinks there is a line leak it will clamp the output and only allow fluid to the side it thinks is still okay. I have seen that valve trip while doing a standard bleed procedure.
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Tuesday, March 16th, 2021 AT 10:12 AM (Merged)
Tiny
JEFF BLANKENSHIP
  • MEMBER
I do not think they ever knew the rear wheels were not braking. They did not know why the front brakes were holding partially enough to make them hot. They said they did a temperature read 560 degrees on on rotor, 600 on the other. I doubt they have a scanner. I would buy one and do my own, if I knew how to use it.
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Tuesday, March 16th, 2021 AT 10:12 AM (Merged)
Tiny
STEVE W.
  • EXPERT
You might try using a pressure bleeder from the caliper end to see if the fluid gets through that way. Or a trip to a better shop to have the brakes checked using the proper tools.
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Tuesday, March 16th, 2021 AT 10:12 AM (Merged)
Tiny
TRAVELINGMAN5352
  • MEMBER
  • 1999 CHEVROLET TAHOE
  • V8
  • 4WD
  • AUTOMATIC
  • 195,000 MILES
I just replaced the vacuum booster and the master cylinder and now there is no fluid coming out to power the rear brakes. I bench bleed the master cylinder before putting it on the vehicle.
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Tuesday, March 16th, 2021 AT 10:12 AM (Merged)
Tiny
KASEKENNY1
  • EXPERT
Okay. How are you bleeding them? Manual or pressure bleeding?

How long have you bleed them? Is the fluid in the master cylinder dropping at all when pumping them?

I attached the manual bleed procedure. Just review it and see if there is anything that you may be missing even though this is pretty straight forward. Thanks
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Tuesday, March 16th, 2021 AT 10:12 AM (Merged)
Tiny
TRAVELINGMAN5352
  • MEMBER
My problem lies within the master cylinder itself as I've disconnected the front line from the master cylinder and there is no fluid coming out when your press the brake pedal.
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Tuesday, March 16th, 2021 AT 10:12 AM (Merged)
Tiny
KEN
  • ADMIN
It sounds like the master is defective or it is not bled correctly. here is a guide to help you recheck your work:

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

Please run down this guide and report back.

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Tuesday, March 16th, 2021 AT 10:12 AM (Merged)
Tiny
TRAVELINGMAN5352
  • MEMBER
Sorry for the late reply. The new master cylinder was bad. I replaced the master, Bench bled it and am know getting fluid to both the back brakes. My problem now is that it's like stepping on a brick, it does stop the vehicle but slowly.
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Tuesday, March 16th, 2021 AT 10:12 AM (Merged)
Tiny
KASEKENNY1
  • EXPERT
If you are lacking assistance, this sounds like the brake booster has failed. The booster is what provides the braking assistance so more than likely you have a leak in the diaphragm.

You can either rebuild it or it would be easier to replace it. Here is the procedure to do this:
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Tuesday, March 16th, 2021 AT 10:12 AM (Merged)

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