2011 Traverse braking problem

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SteelHorseCowboy

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My wife's car, LT AWD with the V6.
She's had it about 2 years now, and in the last month it's done something very alarming twice.
At a low speed, specifically drive thru lane at a McDonald's and a Walgreen's so we're talking about maybe 5 mph, pulling forward a bit and the brakes suddenly don't work.
The first time, she stomped the pedal to the floor repeatedly and managed to stop just short of hitting the car in front of her. She said the pedal was completely "limp" and then it suddenly worked. The second time there luckily was no car in front of her because she rolled right past the drive thru window and into the parking lot. The pedal suddenly went to the floor and locked, and the car slowly rolled to a stop.

About a year ago the master cylinder had a leak, so we had that replaced. All has been fine since then until this happened the first time last month.
We took it back to the same brake shop. This guy has been doing brakes for over 30 years and it left him scratching his head. He went over it from head to toe and couldn't find anything wrong with it at all. He even drove it around a parking lot for a full day and wasn't able to recreate the problem. Told us we should take it to a dealership.

So she did, and now I think they're trying to get her with the old classic "Upsale the Woman" scam.
They've told her she needs new pads and rotors all around, that she has no brake pads and it's metal on metal. I know for a fact that this is utter BS because I look at them myself every now and then and it's the very first thing I looked at when she first reported this problem to me, the guy at the brake shop confirmed it when I called him earlier today. Also, other than the two times it didn't want to stop at all it has great braking power and is smooth, consistent, and quiet.

They're also telling her she needs new tires, which I know is also BS because this is also something I look at myself when I look at her brake pads and rotors (this is a quick and easy walk-around check I sometimes do as I'm leaving for work in the morning). They're telling her she needs an oil change even though I just changed it last month, that she needs her AC system checked, and that she needs her fuel injectors cleaned.
I'm surprised they didn't recommend changing the blinker fluid or replacing the flux capacitor.

Obviously, none of these recommended "repairs" address the problem of random braking failure.

Any ideas why this is happening and how to fix it? Feel free to ask questions.

Check engine light isn't on by the way. There is a creaking noise that seems to come from the pedal itself, but it depresses smoothly and I've assumed it just needs a shot of WD40 and I haven't gotten around to it.

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SteelHorseCowboy

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Obviously if there's leaks I should replace it, but what would oil in it indicate and how would I fix the underlying problem?
Bear in mind I'm not a mechanic, but I'm a fairly talented parts swapper who has managed to keep some real piece of crap vehicles road worthy.

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Doubeleive

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Obviously if there's leaks I should replace it, but what would oil in it indicate and how would I fix the underlying problem?
Bear in mind I'm not a mechanic, but I'm a fairly talented parts swapper who has managed to keep some real piece of crap vehicles road worthy.

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There have been some reports of oil getting in the brake system on newer tahoes, yukons, etc, the vacuum pump seal goes bad and oil gets into the vacuum line and causes the same issue you are reporting, I am not a mechanic either and I do not know how the oil gets there I am guessing it gets sucked in from the pcv system somehow, but I would still suspect the vacuum pump or a vacuum leak especially if everything is working fine normally and the problem only occurs at low speed (i.e. low idle=less vacuum+vacuum leak=problem) i am just guessing here not a professional opinion could still be something else entirely
 

PG01

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I like @Doubeleive line of thought and ill go with that but a random vacuum leak is weird.

On the other hand i also think it could be and abs problem. Years ago there was a recall on my 01 hoe for hub sensors and basically it was a low speed, lose brakes but then pulse and stop with all of this happening within a few seconds, they said it was a buildup of rust in the hub sensors, it happened to me 2x and I crapped myself 2x but no vehicle accident.

The newer vehicles doubie is talking about have electric assist vacuum pump of which a seal fails and lets oil up into the booster rendering brakes useless.

Just talking out loud here.
 
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SteelHorseCowboy

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Thanks for the info y'all! I'll be checking this out for sure.

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iamdub

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I'm with Galante on this one. I doubt your wife was listening as her attention would be elsewhere with being surprised by no brakes, but ABS systems usually make a growling/groaning/rumbling noise when activating. See if she recalls any noises like that.
 
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SteelHorseCowboy

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I'm with Galante on this one. I doubt your wife was listening as her attention would be elsewhere with being surprised by no brakes, but ABS systems usually make a growling/groaning/rumbling noise when activating. See if she recalls any noises like that.

There was actually a groaning/squeaking noise coming from the pedal, but that was all the time and it was just from the pedal itself. I've been meaning to squirt something on it to see if it cleared up. Yeah she may have not noticed one thing or another in her surprise, but that's something that's been going on since we got it, sounds like it just needs WD 40.

I was talking to a friend of my Mother in law who is a mechanic, and told him what was going on. The moment the words got out of my mouth he says "Vacuum problem" and started elaborating on Doubleleive's statement. I showed him this thread and he said the other issue is possible but not as likely. I'm just going to let him fix it.
He also just got my daughter's car put back together yesterday after having a broken timing belt, that's why I was talking to him. I'd never met him before.

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