Brake Noise

[Kdubski]

Car developed a very strange sound upon braking. Only happens when motor is on. Cannot pinpoint a vacuum leak either, so left scratching my head. Sound can be heard coming from what I think is the brake booster. Not a traditional hissing when they fail. Can anyone chime in?

Video with sound: https://youtu.be/FajtIDvTx4o

[eacmen]

Car developed a very strange sound upon braking. Only happens when motor is on. Cannot pinpoint a vacuum leak either, so left scratching my head. Sound can be heard coming from what I think is the brake booster. Not a traditional hissing when they fail. Can anyone chime in?

Video with sound: https://youtu.be/FajtIDvTx4o

Sounds like you got a rubber dog chew toy stuck in there.

Never heard brakes doing that. How do they feel? Lots of travel? Any recent service?


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[Kdubski]

Sounds like you got a rubber dog chew toy stuck in there.

Never heard brakes doing that. How do they feel? Lots of travel? Any recent service?


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Feels normal and fine for the most part. Nothing out of the ordinary aside from the sound. Recent service... yeah an engine rebuild.

[Zack]

Odd sound, could possibly be an internal master cyl. noise. Almost fluid rushing past a seal sounding.

[Kdubski]

When the motor is on I can replicate it with every hard brake. When the motor is off, and the brake pedal builds pressure (3 pumps) the sound is gone.

I'm trying to understand the mechanics of the brake booster/master cylinder before I blindly tear in and make a mess of brake fluid.

[Kdubski]

Going to use this thread as a journal of trying to figure this brake issue out, maybe it can help someone in the future...

MC is where the noise is coming from. Seems like the reservoir closest to the front "bubbles" or "gurgles" when pressing the brake pedal firmly. Brake pedal has normal pressure.

Upon inspection, there is air getting into the MC as fluid is extremely cloudy and brown in appearance (even 3 pedal pumps after topping off with fresh fluid after bleeding). Bled all calipers & slave cylinder (slave cylinder replaced & not bench bled about 300 miles before noise occurred). Fluid from calipers & nipples is clear.

Disassembled most of the right engine bay today to get a good look at lines running to the MC and to the housing just below the MC (not sure what this is, looks like SMG pump?).

Note: Can replicate noise when "punching" the brake pedal.

Images for reference.

[masterofdisaster]

Kdubski Did you find the problem/fix? Getting same noise on my car after changing pads/rotors and flushing... Thanks!

[Kdubski]

Kdubski Did you find the problem/fix? Getting same noise on my car after changing pads/rotors and flushing... Thanks!

Unfortunately was never able to fix it. Replaced the master cylinder and brake booster only to have the sound (or air) return a few miles later. Will save you the headache and just tell you to learn to live with it.

[masterofdisaster]

Unfortunately was never able to fix it. Replaced the master cylinder and brake booster only to have the sound (or air) return a few miles later. Will save you the headache and just tell you to learn to live with it.

That does save a lot of headache and is super helpful - thank you!

[George Hill]

Unfortunately was never able to fix it. Replaced the master cylinder and brake booster only to have the sound (or air) return a few miles later. Will save you the headache and just tell you to learn to live with it.

New or used brake booster?

It sounds like an issue I've seen with failed boosters.

[George Hill]

*I fixed this one with a new brake booster...

https://www.e46fanatics.com/threads/.../post-19164032

[Kdubski]

New or used brake booster?

It sounds like an issue I've seen with failed boosters.

I replaced with used. The sound started after the car sat for 3 months during an engine rebuild. Brake system was untouched but the sound developed ~200 miles after the rebuild. After the booster replacement, the sound started up again at the same interval.

[George Hill]

If its the same noise in the link I posted, you need a booster, the seal could very well be dry rotted and just took a little bit of use to fail.

I fixed that car and my own car documented in that thread with new boosters... my S54 wagon also has a new/used booster that fixed this issue (temporary solution at the time as it was loosing vac assist on long WOT pulls).

[bigjae46]

Brake pedal bushing?