Brake pedal squeal when pressed hard

[BigDogYJ]

So I did some searching and didn't see anything that matched. Nearly every truck I own has Hydroboost brakes so the vacuum booster in this 2013 is not part of my wheelhouse per-se. Since we've decided to keep this rig I've been going through it with a more fine tooth comb.

I've noticed a couple times when pressing the brake pedal kinda hard especially during a panic stop I get this high pitch squeal noise like an air leak or something like that. No warning lights or errors whatsoever and the vehicle drives fine, brakes fine, no rpm fluctuations when this happens, etc.
I can reproduce it even when parked and pressing ******* the pedal. The pedal doesn't sink or anything like that. Not sure what it means. If the vacuum booster needs to be replaced due to this then I'd likely just upgrade to hydroboost. Any ideas?

 

[BigDogYJ]

I had to re-read my post to figure out what I originally typed here....

apparently im being censored for using the words "hard" and "on" next to each other.

Lets try describing it as "pressing firmly on the pedal."

 

[strutaeng]

...those censored word!? LOL

...shouldn't apply to automotive forums, if you ask me

 

[mikez71]

Maybe the check valve if not the diaphragm? idk.

Try pumping it until you're out of vacuum and see if it still makes noise?

Not the pedal bushing squeaking?

 

[OR VietVet]

The diaphragm sounds like is going bad. Does the pedal ever feel hard, like when apply brakes when engine is not running?

 

[BigDogYJ]

ok so I played with it a bit tonight and the pedal firms up after the 2nd application while the truck is off. pushing and holding on the pedal while starting causes the pedal to sink id say beyond 50% which is likely normal.

However I was able to confirm that pushing the pedal fully to the floor or as far as it will go does not cause the noise. It appears to only occur with moderate pedal pressure about 50% travel or so and it slowly fades out then it won't repeat until im assuming vacuum builds back up again. when pressing the pedal further it seems to stop. Normal driving I don't ever hear it but if I have to stop sudden or harder than usual (as least for me -- im a pretty mellow driver, generally) then I usually hear it and honestly my wife looks at me funny because the noise occurs if I have to apply brakes harder than I usually do so its pretty apparent. tried to get a video of it here. hopefully this helps.

And yes listening to this video it sounds like the pivot bushing or whatever it is could use replacement too but I think that's separate from the bleed sound im hearing.

 

[mikez71]

Holy mother that's loud!
Could disconnect and plug the booster hose to verify.. But I can't imagine what else it could be..

And it looks like you have an Autosync!

 

[BigDogYJ]

yeah I can try that next and report back.
Yes I use it for a few nice features and displaying engine/trans data on the DIC when im curious.

 

[Doubeleive]

you could try replacing the check valve but it sounds like a internal seal

 

[Bronson357]

I can't exactly tell but is there any chance it's coming through the speaker? Bad ground when you move the pedal?

 

[BigDogYJ]

Interesting thought. It does seem to change slightly when I change the pressure on the pedal. And it doesn’t seem to be affected by moving the adjustable pedal position. But worth going under there to take a look. I’ll have some time tomorrow to pull the vaccuum hose and plug it then see if I can reproduce it. I’ll update after.

 

[OR VietVet]

Did I miss where you said you have adjustable pedals or did you just now share that?

 

[BigDogYJ]

No I didn’t mention it prior. I actually assumed that all gmt900’s had them. Or at least I thought so. That might be wrong. Sorry. Yes it has adjustable pedals but moving them to different positions along their travel doesn’t seem to make any difference in the squeal noise. So not sure that would change it.

Sorry was doing family stuff today so didn’t test without the vacuum hose plugged. I’ll try tonight after baby is asleep.

 

[OR VietVet]

Sorry, I hate hate hate assuming.

 

[dkad260]

Based on the duration of the sound, I agree it sounds like a ruptured booster diaphragm. I can't think of anything else other than the check valve.