Help identifying this noise that occurs with brake pedal pressure

Sudo

Sudo

TJ Enthusiast
Joined
Feb 22, 2019
Messages
330
Location
Arizona
On a very steep decent and needed to stop and while applying very firm pressure on the brake pedal a high pitch noise is heard. Noise changes pitch slightly when applying slight pressure changes on the brake pedal.

Anyone experience this or know what causes it? Remedy?

Tagging the brake wizard @mrblaine
 

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  • 20210116_101937.mp4
    12.2 MB
mrblaine said:
Sounds vacuum related for sure. But without ever having heard that exact thing, I'd start with the check valve, line from the manifold and try to recreate the symptom on flat ground.
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Thanks.

What are some other symptoms that a leaky check valve might cause? I'm assuming it's there to hold vacuum on one side of it. I have some reading and searching to do. I appreciate the input.
 
Sudo said:
Thanks.

What are some other symptoms that a leaky check valve might cause? I'm assuming it's there to hold vacuum on one side of it. I have some reading and searching to do. I appreciate the input.
Click to expand...
Hard pedal right away as soon as you turn the motor off if the leak is bad enough.
 
Would very firm, not standing on brake pedal but very firm pressure on pedal cause a seal to leak ? I don't know the break booster mechanics as to whether its even plausible

Looks like I need to find a hand vacuum pump to test check valve or is replacement the way to go?

Screen Shot 2020-10-28 at 6.01.51 PM.png
 
Goatman said:
Well, just listened to that file and now my dog is going APE💩! Like bouncing off the windows and doors! 🤭
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Yeah, should have put a warning in the initial post. Its an annoying sound. Almost dumb and dumber annoying.
 
ok, in park ...jeep running on flat ground and apply brake pedal pressure very firm. Just barely let up pressure on pedal and I can hear the noise. if brake pedal is "throttled" just right you can hear the sound. Its a short specific range and slight pressure changes on the brake pedal will make it come and go.

Very Strange...

Anyway know a good reference for understanding the brake booster? I'm still learning how it works so I can understand what might be occurring.
 
Longshot here...
Could it be a slight crack or split in a brake line sucking in or pushing out some air/fluid causing just the right harmonic to cause that sound? Any fluid leak or drop in level in the master?
 
Goatman said:
Longshot here...
Could it be a slight crack or split in a brake line sucking in or pushing out some air/fluid causing just the right harmonic to cause that sound? Any fluid leak or drop in level in the master?
Click to expand...
Just checked reservoir and no drop in level noticed. Noise is coming from brake pedal to booster. Does sound like air whistling with just the right position on brake pedal.

Push rod on brake booster....is there a seal for pushrod that with enough pressure would cause air to escape?

Appreciate the discussion.
 
I took the advise from here , I greased everything and where there was no zerk I bathed it in penetrating oil and today...noise gone.
Thanks!
 
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