Master Cylinder Noise?!?!? (Entertaining Video Inside)

[83hurstguy]

My C6 brake swap project has been cursed. My first G-body master cylinder, 6 years old, kept generating air bubbles even after several bench bleeding sessions, so I bought a NEW master (not remanned) with reservoir from O'Reilly Auto yesterday, since they were the only people with one in stock.

Bench bled it via the plugged port method yesterday, got the air out in about 10 minutes. Things were going well...

Put the new master in the car late this afternoon, finally got all the air out of the brake system, but now the brand new master cylinder is making a moaning sound that is obnoxiously loud. See video below, where I released a bleeder valve with the wife pushing the brake pedal.


http://www.youtube.com/watch?v=uyiin-Ah3Y8

Anybody ever seen this before? It's hard to tell if the booster is doing it instead of the master, but that booster was making bleed cycles two days ago on the last master perfectly quietly.

[83hurstguy]

Overwhelming response... hmmm...

When the engine is running, it's really hard to discern if it's making the noise or not. It sounded like it was.

Here's a video with the car running (without pumping the brakes), followed by what happens when pumping the brakes after shut down.


http://www.youtube.com/watch?v=bzDCv7E5spo

The pedal travel seems a bit long with the engine running, you can hear the pedal stroke shorten and pump up after engine shutdown. Wondering if trapped air is causing that along with the noise? I've never had this car moving with this brake combo, so it's hard to know where the pedal position needs to be. These quick take up masters tend to have a high pedal position, and this one seems low. Hard to believe it's air when there's no bubbles with the master ports plugged and nothing is coming out at the calipers.

[MrQuick]

thats a weird one.

[rchaskin]

sounds like the booster company put a baby lamb in there to actuate the master.....LOL

Do you think this could just be the vacuum exiting the booster?
Or some sort of bypass inside the booster when the motor is not producing vacuum??

Do the brakes ever get correct pedal feel?
If so, i would take it outside to see if it makes this sound while running.

Very weird sound.

Good luck.

[83hurstguy]

Thanks Randy. I have it on jackstands yet for bleeding, hate to back it out of the garage just to put it back in and re-pull all the wheels.

The booster seems to pass the normal checks (pedal drops with engine running, holds position under load with engine off, and also pumps up when the engine off). With the master off tonight, I put resistance on the booster pushrod while she cycled the pedal. No noise other than some air rushing out.

Took the master off tonight, confirmed there was no air in it by using the clear hose method to re-bleed the master (had originally used the plugged port method). You could hear a very slight squeal-type noise from the master on the bench, though it was nowhere near as loud as it was on the car. I'm bringing it back to O'reilly tomorrow for a warranty exchange... see what happens tomorrow night.

[rchaskin]

Maybe it is the master then.
You never know the story behind auto parts these days.

[83hurstguy]

The new master is quiet (third one now). It was a bad unit after all... however, now I'm back to fighting air entrainment in the front circuit, which was the problem I had with the first master. Sigh... :banghead:

[rchaskin]

I'm a mechanical engineer, and I refer to situations like this as the "End User Maximum Discomfort Policy" LOL.

I still cannot believe the sound that master made......

[83hurstguy]

Same profession here, though I'm embarrassed to admit with how poorly most of my projects go. Lol... I plan to stash that line for use, though I will give you the credit! Thanks.

[72mojave]

I installed a 4-wheel disc kit on a Chevelle and the booster made that same noise BEFORE the master was even installed. I pressed the pedal down to check for interference with wiring, and I thought I stepped on a baby lamb.