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Vehicle: 2000 Blazer v6 4.3L

Symptoms:

  • Brake goes to the floor before braking. You have to push hard to stop. Easy to "skid" tires.
  • Brake light is on.
  • The day before they worked perfectly fine, and the next morning they went to the floor.
  • If the engine isn't started the brakes seem fine, but after starting the engine they go to the floor.

Recent Maintenance:

  • The whole brake system was replaced about a year ago.
  • Since then the Spark plugs, Spark plug wires, Vacuum lines, and Cap & Rotor have been replaced.
  • *Changed the master cylinder today. No change, brakes still go to the floor, they still work, but they start working in the last 10% or so of pressing the pedal.

Attempts & Checks so far:

  • Double-checked the Vacuum lines thinking it might be the Booster, however the booster would make the brakes harder to push not softer and there weren't any issues with the lines.
  • Checked for leaks: Haven't seen any.
  • Bled the brakes: Didn't change anything.
  • The front brake pads are worn a bit but not shot by any means and the rear brake pads are near perfect condition.

Concerns: I keep reading online that it could be a master-cylinder failure when I google these symptoms, however if I google the symptoms of a master-cylinder failure they appear slightly different as I can break, it just goes to the floor before doing it and it's consistently like this instead of being a one-time thing.

Could it be the Anti-Lock Break System (ABS)? I know the ABS has its own light on the dashboard (which isn't on) but is it possible that it's causing the issue with the breaks?

Does anyone know what could be the cause of this?

EDIT: Changed master-cylinder, no change. Any Ideas?

|improve this question
  • I have a few questions. When you bled the brakes was it with the help of a second person, hand pump pressure bleeder, pneumatic pressure bleeder? When bleeding was everything normal (air at first followed by nothing but fluid once bled)? Was the master cylinder bled as well (on a bench and/or on the vehicle?) If you pump the brakes does it start to get some pressure in the pedal or no matter what it goes to the floor before you get any bite? – cinelli Aug 30 '14 at 1:07
  • Just noticed the solutiion was posted. Dissregard the comment :) – cinelli Aug 30 '14 at 1:08
  • +1 for having a fairly big engine car! I hate low CC cars (ie: 1.6), they arn't effortless and are so slow lol. – Dan Jul 13 '15 at 7:51
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That sounds very much (no, it sounds exactly) like either of two things: either the brake fluid in the master cylinder is very low, or the master cylinder has failed. If anything else were the cause (caliper or wheel cylinder failure, line leakage), then you'd find brake fluid either on the ground or on the inboard surface of one of your tires.

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  • Is there a way to verify this or possibly fix this without replacing the master-cylinder? Just curious as it seems they are pretty expensive, so I don't want to replace something so expensive to have that small chance it wasn't the problem . (No trying to insult your judgement or anything, just have found in the past solutions aren't always as they appear). – Shelby115 Aug 24 '14 at 19:48
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    No problem - no offense taken. One way I know to test the master cylinder is to buy two very short brake lines (or one longer one) with fittings that match those on the master cylinder. Cut cut to only several inches long, retaining both fittings. Kink over the cut ends and pinch them tight with ViseGrips or something similar (ideally, braze them shut). Now disconnect the two "real" brake lines (on the vehicle) from the master cylinder and attach these two short stubs in their place. Press the pedal - if the master cylinder is bad, the pedal will still go to the floor. – TDHofstetter Aug 24 '14 at 19:58
  • Changed master-cylinder. No dice. Any other thoughts? – Shelby115 Aug 26 '14 at 21:32
  • @Shelby115, then only one of two possibilities can be true, both of which has already been addressed in your original question: Either you have a brake fluid leak somewhere or you haven't fully bled the brakes. – TDHofstetter Aug 26 '14 at 21:37
  • We found a leak that wasn't there before? Is it possible it was the master-cylinder and the new leak is causing the same exact symptoms? Additionally the new leak appears to be coming out the back where the piston is(of the master cylinder that is)? – Shelby115 Aug 26 '14 at 21:54
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We solved the issue today. It came down to a sneaky leak in the back brake lines. We fixed that and then had to bleed the breaks a ridiculous amount. After bleeding the back brakes about 10-15 times each the brakes no longer went to the floor (and fixing the sneaky leak of course).

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That to me sounds like your master cylinder has failed as the first poster pointed out. The master cylinder will keep the brakes up once it is functioning the way it should, the minute there is any change in the feel, it is either the booster (harder feel) or Master Cylinder (softer feel or dropped brake pedal).

Also, brake pedals tend to go to the floor when there is air in the line and they need to be bled but this only happens when the pedal is depressed. Finally, there is a little switch under your dash that is held down turning the brake lights off when the brake is up. Once you sort the brake being to the floor out, then the lights will work as they normally do.

Replace (or rebuild) your brake master cylinder and flush out all old brake fluid and then refill it taking care to bleed all air out and then you should have perfect brakes.

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  • Did you see the edit at the bottom? I did replace, I am having a small leak with it oddly enough with the new one, going to rent a flairing tool soon and try reflairing to see if that fixes the issue – Shelby115 Aug 27 '14 at 23:23

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