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Brakes will not disengage after 10-15 minutes of driving.


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On 12/30/2023 at 12:28 PM, BrianBrianBrian said:

Interesting.  I purchased the ac Delco ones from advanced Auto parts.

Were the old pads you originally purchased sticking to the rotor? 

That's a lot of brake dust for OEM pads... I can't really make out what motion is making the clanking sound in the video, either way that isn't normal either. 

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Quote

 

Action Taken When the DTC Sets

Service Brake Assist message is displayed on the driver information center

 

Do you get this message? 

 

There used to be a topic/TSB about the vacuum pumps failing that you might look in to as well.

 

The trouble code you posted looks more like a sensor issue than anything else. That wouldn't explain it manifesting in a mechanical fashion though...

 

If the brake booster has a leak allowing vacuum to leak in, it could cause the sensor to see a low vacuum condition that shouldn't exist (triggering the code), while at the same time applying brake pressure without pedal input. 

 

Shutting off the engine removes the vacuum source and pumping the brakes releases any stored vacuum resetting the conditions. 

 

I think maybe the brake booster is the culprit.

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1 hour ago, asilverblazer said:

 

Do you get this message? 

 

There used to be a topic/TSB about the vacuum pumps failing that you might look in to as well.

 

The trouble code you posted looks more like a sensor issue than anything else. That wouldn't explain it manifesting in a mechanical fashion though...

 

If the brake booster has a leak allowing vacuum to leak in, it could cause the sensor to see a low vacuum condition that shouldn't exist (triggering the code), while at the same time applying brake pressure without pedal input. 

 

Shutting off the engine removes the vacuum source and pumping the brakes releases any stored vacuum resetting the conditions. 

 

I think maybe the brake booster is the culprit.

I thought brake booster was only to assist in the pedal not restrict it from releasing?

 

I did have the truck serviced for the Vacuum Pump thing back in 2019.  They replaced both the pump and the belt. 


I am aware of a safety recall Part 573 Safety Recall Report   There are several relatable issues that I'm having and what this recall addresses, however per the recall it only pertains to trucks with 3.08 ratio.   Mine is not.  But who knows at this point 

Edited by BrianBrianBrian
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15 minutes ago, BrianBrianBrian said:

I thought brake booster was only to assist in the pedal not restrict it from releasing?

The other thread you linked to that had similar symptoms that were "resolved" by washers on the pushrod (summarizing) indicates that something in the booster/master cylinder assembly is at fault. 

 

I can't think of a way that the master cylinder would cause a vacuum code.

 

The booster though could (I'm drawing this conclusion based on the booster working off vacuum).

 

Without a more thorough diagram of the booster/master cylinder its hard for me to describe how... but I'm thinking the valve that controls the vacuum's action on the power diaphragm isn't shutting based on the pushrod's position (washers altered the pushrods position in the other thread and fixed this). Meaning that even though you've released the brake pedal, vacuum is still being applied to the power diaphragm resulting in the brakes being applied without pedal action.

 

The vacuum leaking off without the engine running is allowing the power diaphragm in the booster to retract and release the brakes. The master cylinder I don't think would bleed off like that. 

 

I'd need to study some diagrams and symptoms more carefully to confirm my hypothesis...

 

You could pop the vacuum line off the booster and cap it. Then drive (carefully, you wouldn't have any power brakes) to see how it changes the brakes action. I'm working from memory here, (see bolded sections above) but it should either result in the problem not appearing at all, or appearing immediately. You might also be able to pull that vacuum line off the booster when the brakes have locked and see if they immediately release (I can't recall the presence of a check valve on it).

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The picture attached isn't accurate to these trucks but what I'm getting at is the "poppet valve" in the image isn't fully closing or is leaking this would apply the brakes until the vacuum (on the vacuum side) bleeds off.

 

I'm not ruling out the master cylinder yet either, the vacuum codes are why I'm more interested in the booster.

image.png

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Thank you for taking the time to aid in my troubles!   I just got back from the dealership and I think you got your answer into the voting booth just in time to win the prize, lol.  Sorry, fresh out of prizes after the cost of this roller coaster.

 

Here is what they had to say:

 

They are going to replace the MC and the Brake Booster.  Also they are going to replace the Vacuum pump + Belt (for the 2nd time) and get it covered under the recall (again).  Technician drove it and (thankfully)experienced the brake drag on the test drive. He opened the hood and disconnected the vacuum hose to the brake booster.  While this obviously made braking a harder, the brake drag was gone and he was able to get the truck back to the dealership. I was told that they also found Hydro fluid in the booster.  
So that's all I've been given... They didn't really tell me what the exact failure point was other than its somewhere between the Vacuum pump and the MC.  Thus, replace it all and it should be fixed. 

 

Should I be asking more questions to the dealership about this problem, or it is what is?


I'll give another report back for the purpose of this thread after I get it home.  Thank you to everyone here that helped.

oh  If anyone is curious, $1,333  

Edited by BrianBrianBrian
missing word
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19 hours ago, asilverblazer said:

The picture attached isn't accurate to these trucks but what I'm getting at is the "poppet valve" in the image isn't fully closing or is leaking this would apply the brakes until the vacuum (on the vacuum side) bleeds off.

 

I'm not ruling out the master cylinder yet either, the vacuum codes are why I'm more interested in the booster.

image.png

Is the poppet valve part of the Brake Booster? As in, will it get replaced when they replace the BB. 

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2 hours ago, BrianBrianBrian said:

Screenshot 2024-01-31 140425.png

Do your research on this vacuum pump extended warranty. IIRC, if they find oil in the vacuum line to the booster, the warranty was to replace the booster as well under warranty. 

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Final verdict: Brake drag culprit was caused by a leaking master cylinder that eventually compromised the brake booster.

Fluid from the Master Cylinder was slowly leaking into the brake booster for quite some time.  Tech said about a quart was drained from the booster.  I asked how long this was going on and the answer was approx. 3 years~?  

Anywho,  thank you to everyone that helped

image.png.465e22ef45bcddbac77b6fe37e69b24f.png

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