Loss of power when Braking - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 04-05-2006, 08:26 PM   #1
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Default Loss of power when Braking

This is a new problem about a year after I replaced the crank sensor so I can only post what I've learned so far.
My girlfriend told me my car was stalling out when she hit the brakes. I thought: stalling while braking? never heard of it. Last week, it happened to me while I was driving. However, the engine did NOT die. It was as if I had lost power: car slowed down, cd player cut off, and the warning sound (as if I was out of gas). It only lasted a second and then everything was back to normal. It has only happened once to me so these are the only clues I have. I do suspect it only happens while braking and is fine upon releasing the brake pedal and if the brake pedal was pressed for an extended period of time (like coming to a complete stop) it would cause the engine to stall.

Any and all help will be greatly appreciated.
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Old 04-05-2006, 08:54 PM   #2
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Welcome to Bonneville Club! Please add the year and model of your car to your signature so that we can help you more easily.

Just a first guess, but you might have a bad diaphragm or other vacuum leak in the power brake booster. When you apply the brake, you open up the vacuum leak, and the engine, at idle, sucks in too much air to run properly, so tries to stall.

You can check this out for free by unclipping or unclamping the big vacuum hose that runs from the intake manifold to the brake booster. Plug the hole tightly in the intake manifold and drive the car. BE CAREFUL, YOU WILL HAVE NO POWER BRAKES!

Find a safe area to drive the car to test this out. With no power assist, the brakes will require a LOT of force at the pedal for the car to stop. Anyway, get the car going with plenty of extra stopping room - then apply the brakes and see if the car still tries to stall. If it no longer wants to stall, you probably have a leak in the brake booster circuit. It it still wants to stall, the problem is elsewhere.

But the fact that the brake booster uses a lot of vacuum may still indicate a vacuum leak elsewhere on the engine. Look for leaking connections or bad hoses.
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Old 04-05-2006, 09:16 PM   #3
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Thanks for the quick reply!
Let me back up a little and say that for about a week before I ever noticed an engine stall problem, I would notice only the cd player and warning sound (I wish I knew a more technical term) and I had not noticed the correlation between this and the brakes. The stalling issue has come up more recently which leads me to believe that the problem is getting worse.

I have actually been hoping this would happen again so that I could further investigate exactly what is happening at the time of stalling or near stalling. Does this still sound like what you are describing?
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Old 04-05-2006, 09:46 PM   #4
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I agree with Bill Buttermore....

Do me a favor... Start the car let it run for a brief amount of time... Shut the car off and listen for a hiss right after you turn the car off.. This hiss should last more than a few seconds... If you hear this hiss you may have a bad brake booster...

But what you describe almost leads me to believe that the booster is bad..

Check it all out and get back to us..

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Old 04-05-2006, 09:53 PM   #5
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Will I hear this hiss better inside or outside of the car?
and
Could this sound be a hiss/squeak/chirping sound or just a solid hiss?


p.*.: Gotta love that red 95 SE!
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Old 04-05-2006, 09:56 PM   #6
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Might be a soild hiss.. You'd hear it better outside the car... What your looking for is a ruptured diaphram in the brake booster... It will hiss as it looses vacume...

While its idling hit the brakes and see if it changes the idle as well..

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Old 04-05-2006, 10:23 PM   #7
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I will do that and post it here.
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Old 04-06-2006, 11:29 AM   #8
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Remove and thoroughly check the vacuum hose running from the rear of the intake manifold to the booster before replacing the booster. Not only is it cheaper to replace, it'* more likely to fail. When I replace them, I just use aluminum tubing from the hardware store to replace most of the hose and use a short section of the hose for the fittings on either end.

Your car definitely has a vacuum leak.
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Old 04-06-2006, 05:49 PM   #9
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Quote:
Do me a favor... Start the car let it run for a brief amount of time... Shut the car off and listen for a hiss right after you turn the car off.. This hiss should last more than a few seconds... If you hear this hiss you may have a bad brake booster...
I hear no hiss and no it does not change my idle. Would a leak be an intermittent problem?

On a side note: I don't know whether this is related but my Bonnie seems to have some strain on the electrical system: Whenever I use an accessory such as a power window or applying the brakes, I notice things like my volt meter drops, my interior lights dim, etc. Sorry I'm getting off topic but I keep thinking Electrical.

I appreciate everyone'* help so far. So the power brake booster is located?....driver'* side, firewall, high or low?
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Old 04-06-2006, 06:00 PM   #10
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well as for the location of the brake booster it is the big round thing sticking out from the firewall just behind the MC (where the brake fluid tank is located)
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