So I've been chasing this issue for a few days and I'm at a loss at this point. I recently pulled my brake master and booster as part of my pedal refresh. Gave the master a flush and re-bleed, and repainted the booster after cleaning up some rust from an old leak. After putting everything back together I bled the brakes and this is where the problem began.

After a lot of diagnosing I've determined the noise is coming from the back of the booster and the sound can only be heard on the cabin side of the firewall. Could this be symptom of the booster failing? Maybe something with the master? The strange thing is that for the first or second pedal presses there is no noise and it only starts on the third to fifth pedal presses, slowly getting louder with each press.

My guess is that is either something with the pushrod or a vacuum issue. I never adjusted or otherwise did anything to the pushrod so I don't know why it would suddenly be causing problems. And the car is a roller so if it is a problem with vacuum, there's not much that I can really do at this point. Any advice is greatly appreciated and I've included a video though the noise is louder in person.

 

It sounds like a spring making that noise to me - only ones present I can think of, are in the booster or the wound torsion spring at the pedal pivot.

Usual bugbear of the push rod clevis and pin into the brake pedal ovaling out the softer hole doesn't appear to be an issue, unless the lost motion is hidden.


.

 

I've heard the Nylon pedal pivot bushing make a creaking noise - a bit of spray-on lube made it stop. And since you can only hear it inside, and it gets louder with subsequent pedal presses, that may be it.

 

And we have a winner! I greased both the bore and outside faces of the bushings during assembly so I didn't even think to check them. Turns out they were spinning and rubbing against the actual pedal. Shot a bunch of spray grease in the gap, gave the brake a couple of pumps and now everything is quiet again!

I'm glad it was something simple, I was dreading the thought out pulling everything out of the car again.

 

Creaking is usually a stick-slip phenomenon so the pedal bushings immediately came to mind, especially since I had that happen.