Hard Brake Pedal? The Real Cause and Diagnostics - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 05-03-2007, 10:38 AM   #1
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Default Hard Brake Pedal? The Real Cause and Diagnostics

After one day my break pedal went to the floor for a second time last month (first time they bleed air out of the system and it worked ok for a week) i went to the shop. Lines and pads were checked everything was fine.
Diagnosis was "Master Cylinder Failure" and it was replaced...
Ever since my break was kinda hard but i didn't have time to get to the shop to show it to them. Plus it'* my first car and i don't really know who hard pedal should be.

But last night i was driving another car and had to drive mine right after it, and difference in force needed to be applied to the breaks nearly caused me an accident.

Please let me know what can be the problem and how can i single it out without getting ripped off... Because the master cylinder that was replaced was a year old and i don't really believe it could have been real problem.

Thank you
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Old 05-03-2007, 03:07 PM   #2
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I wonder if your brake booster (the big, round vacuum can behind the master cylinder) has failed or has lost its vacuum supply. That would make the brakes much harder to operate. Check the hose that goes from the intake manifold to the booster to make sure it is connected and in good condition. Check to see if the diaphragm in the booster unit is good by disconnecting the vacuum supply hose at the booster with the engine idling. The idle should change drastically when you do this, as you are adding lots of un-metered air to the engine. If there is no change in the idle, that would suggest the diaphragm in the booster is ruptured. Also, check to make sure the vacuum supply hose is not internally blocked by placing your thumb over the end of the hose you disconnected with the engine running. You should feel a strong vacuum. If not, the hose is blocked.
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Old 05-03-2007, 03:18 PM   #3
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I'd definetly look into it being the brake booster. My thunderbird'* brake booster was bad and I had the same problem. Once it was replaced, whala! Better brake pedal.
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