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Brakes - I've mentioned this before. Now again.

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I've had my truck in twice with brake concerns when backing. Pedal appears to lose 90% of the boost and pumping generates no additional pressure (maybe modern brake systems aren't supposed to).

 

First visit, truck picked up after "cannot duplicate." Second time, mechanic said he bled the brakes.

 

Today - after two additional occurrences, I dropped off again. Last week, backing into a spot in a parking garage after a 100 mile trip, the brakes almost disappeared. It's a horrible feeling in your gut, but with much care I can get the truck where it needs to be. I kind of ignored it.

 

Today, in front of daughter's apartment, after a 30 mile trip and nose up toward a moderate hill, it did it again when I backed to get parallel with her yard. Now THIS one got to me. I got a pretty good shot of adrenaline.

 

Only when backing at slow speeds. I can't purposefully duplicate it.

 

If I have a loss of braking - maybe this is incremental, but could lead to complete failure - I have potential to cause damage to others, property, etc., insurance could spike and if it happens while I'm driving the truck on company business, I don't even want to consider the ramifications.

 

So they have it. I have a loaner. Everyone was nice. But I'm not sure if they think I'm crazy. I tried to assure them I dont have time to be screwing around imagining problems.

 

WTH might be going on? It doesn't appear to be a systemic problem (see: transmission) but a one-off mechanical/electrical intermittent failure. It happens. But it needs to stop.

Justin101714 Enthusiast

Justin101714

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I know exactly what it is because I had a customer complain of that same thing.

 

1. The 5.3 is supplemented vacuum to the booster by a vacuum pump

2. If you're constantly on the pedal pushing in about frequently enough will cause you to bleed all vacuum from the power brake booster, the vacuum pump turns on before all vacuum is lost but in my opinion a little too late. This is why you get this fading pressure feeling and there is no fix for it. You could put 100 boosters and vacuum pumps on the truck and it will ALWAYS be the same. Now, if you're like most others that park and use the pedal a few times to get into a spot, then you'll most likely not encounter this problem. So in short, this isn't a problem the dealership is going to be able to fix. The vacuum is bled off faster than the pump seems to replenish. So at this particular moment, there is no part they'll replace that will make it better. They may come out with a better pump in the future. Everyone can try this and see what I'm talking about. Just stick the truck in reverse and let the vehicle roll while constantly going up and down on the brake pedal, you'll notice the power assist fades over several applications.

 

 

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Boardmember Senior Enthusiast

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Thanks Justin. I will have his discussion tomorrow.

 

I would think if this is endemic in the design, enough others would have had the opportunity to get the same adrenaline blast I got this afternoon.

 

Is it possible it's a matter of degree? I mean, might one system be better/worse that others?

Justin101714 Enthusiast

Justin101714

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Thanks Justin. I will have his discussion tomorrow.

 

I would think if this is endemic in the design, enough others would have had the opportunity to get the same adrenaline blast I got this afternoon.

 

Is it possible it's a matter of degree? I mean, might one system be better/worse that others?

It's possible I guess, mass produced parts can yield different results in a small way, especially when they are made by several different plants.

 

The vacuum assisted systems aren't really new, they existed for a good while actually. You would figure on a full size truck with towing potential that the brake system would be of paramount importance....

 

Could it be better? Absolutely! Could it be worse? Definitely! When I'm backing up I only touch the pedal twice, so I will almost never experience this. Even if I'm pulling somewhere, I would have this happen either. You should try to leave your foot on the pedal and ease in the area instead of allowing the pedal to travel up or down which will drain the vacuum faster, the pump on/off time just can't keep up.

 

 

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Dnt Senior Enthusiast

Dnt

Posted
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Does the 6.2 engine use the same vacuum pump for the brake booster?

Boardmember Senior Enthusiast

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Have you experienced this?

Am I - and Justin - the only two here...?

 

I would think the liability for GM for an acknowledged issue such as this is huge. Time for some customer care dollars to help me buy a new truck?

Ichie123 Enthusiast

Ichie123

Posted
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I think I've been having the same issues. Though my display has told me my "brake assist" needs servicing. On star has also emailed me to bring my truck in to service my abs and my stabilitrack. It only started while I was in NYC for work. Has only happened once since being back home in Mississippi. Did not happen the entire way home. Was able to forcefully duplicate. Unfortunately my truck is in the shop now getting repaired for damages done by valet services in NYC. Guess I'll know if I can duplicate again after I get the vehicle back.

Also mine happens both forward and reverse

Boardmember Senior Enthusiast

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Not that anyone but me continues to worry about this (a good thing), but an update to this is I received a call from the Service Manager yesterday afternoon and he had been conferring with some entity - I plan to ask who, but didn't yesterday - and was instructed to replace the brake vacuum pump. Ok. That sounds logical based on what I've experienced. Later this week...

 

Wish us luck.

Donstar Senior Enthusiast

Donstar

Posted
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"If I have a loss of braking - maybe this is incremental, but could lead to complete failure" If the issue is the vacuum pump, and it fails, the brakes will still work, won't they? I realize that this problem needs to be resolved.

Justin101714 Enthusiast

Justin101714

Posted
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"If I have a loss of braking - maybe this is incremental, but could lead to complete failure" If the issue is the vacuum pump, and it fails, the brakes will still work, won't they? I realize that this problem needs to be resolved.

they will work. But they will have less boost assist

 

 

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Zasker1 Enthusiast

Zasker1

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I need to follow this thread I have had this exact same type of issue for the break pedal just seems to fall all the way to the floor at ultra low speeds it is happen multiple times when coming down by 100 foot driveway which is about a 15% grade

Boardmember Senior Enthusiast

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Correct Justin. It doesn't feel as the brake performance is ZERO but it feels no boost. That's it. I've driven for many years. I recall the feeling when an old vehicle engine stalled out while rolling (clutch, anyone?) the brake pedal lost its power assist. As did the steering. Kind of like that.

 

Not sure how this device works, might it have a leak in a connection that is triggered by specific conditions? -> reverse, slow speed, modulating vehicle travel by applying the brake, temperature (I've suspected the vehicle being warmed up through driving might impact, but who knows?). Might It be me bleeding the vacuum somehow?

 

Again, I cannot purposefully make it happen. But tomorrow is the day. How long do I experience no prob before my confidence is back?

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