Hey all, posted recently about how my brake pedal would fall to the floor randomly a few times over a few months. Also, twice it was hard to actually brake. Everyone seems to think it's the master cylinder, which I suspect it is as well. Anyways, there is another development I wanted to ask about before delving into this problem.

I hear a whining noise coming from the rear driver side wheel well. It's not there when the car is sitting ever, regardless of RPM. It starts once the car gets going and it starts pretty quick (even under 10mph). It is not consistent sounding, the pitch changes, sometimes you can't hear it at all, but it's there on and off always.

What does this sound like to everyone? Brakes? Could this in anyway explain for the pedal falling to the floor or is that independent of this? When I brake, I hear a different sound that is kind of like grinding by the way. Thanks,

David

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1985 300D. 179,000 miles.

Take your wheel of and have a look.

What happens when to the sound when the brakes are engaged?

What happens to the sound up you engage or slightly engage the parking brake?

CV-axle boots in good condition?

'Need to start Eyeballing ALL of the above.

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'84 300SD sold
124.128

When the brakes are engaged, I can hear a separate grinding noise from the brakes, although I can't tell which brakes that's coming from.

I don't believe parking brake plays any role in this. Although, when the parking brake is engaged, the car isn't moving and therefore it wouldn't make the sound.

Not sure about anything else, gotta get at this tomorrow.

Anyways, I guess one of my questions is.... is there any way that the pedal falling to the floor could be related to this? Or the master cylinder failing? For instance, could the master cylinder failing cause brake fluid to not go to the rear left brake and therefore create a whining sound? Or am I looking at two separate problems?

Thanks,
David

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1985 300D. 179,000 miles.

this could be brakes, here is a theory

your rear passenger caliper has a leak to some degree and holds no pressure. that would explain the sound in the back because the pads are simply floating on their pins and deciding when and how long they want to make contact with the rotor. and by contact i mean a slight annoying rubbing.

also explains why your pedal made it to the floor, a bad line or caliper will allow air into the line and lose pressure for the entire system. i would pull that rear wheel for initial inspection, and make sure you have brake fluid in the master. sound more like a line/leak more than a master. do all the wheels while you are at it.

just a theory because i am not there to see

[QUOTE=davidd;2475604]Hey all, posted recently about how my brake pedal would fall to the floor randomly a few times over a few months. Also, twice it was hard to actually brake. Everyone seems to think it's the master cylinder, which I suspect it is as well.


David ... how can you continue driving a vehicle of any kind that has failing brakes ?? You state "my brake pedal would fall to the floor randomly" !!

What the hell is gonna happen if a 6 year old wanders out in front of you at the time the brake pedal falls to the floor... randomly ???

There are two currently in Vanderbilt who wandered out in front of a car WITH brakes ! With no brakes, both would be dead.

Park it until it is again road worthy. Killing someone for your lack of desire to fix the issue is sure not worth it.

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1985 300D 198K sold
1982 300D 202K
1989 300E 125K
1992 940T

"If you dont have time to do it safely, you dont have time to do it"

"The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."

[QUOTE=TnBob;2475975]
I never said I'm driving it around. I live in the middle of nowhere, so I can test drive it around and listen for noises with no worries.

I continued to drive the car after the first couple times the pedal hit the floor because the car still braked totally fine. I thought I had a vacuum problem or something else and started researching. But then the problem went away for months. The brakes were firm and 100% fine. Then a few weeks ago, the pedal hit the floor and it was hard to brake, this happened two times the same time I was out. I got the car home and haven't been driving around since then, except around on the dirt road outside my house to test things. So rest assured, I'm not going to kill anyone.

David

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1985 300D. 179,000 miles.