Mysterious brake fluid loss 2007 Cobalt

[901Memphis]

My buddy has a 2007 Cobalt coupe and the low brake fluid light came on again this is the 3rd or 4th time in maybe a year or less It's came on and there are no puddles or drops showing anywhere on the pavement.

I told him he needs to get it checked out but he's cheap and keeps adding fluid. I inspected the front pads visually through the wheels and they appear to be very meaty still. I suspect that the rear drums are original maybe they are worn to nothing by now? Vehicle has about 80k miles ish on it.

I'm also wondering is it possible to leak brake fluid where it wouldn't be seen?

The brakes do make metal sound grinding but only when wet. I don't have time to look at it but would like some input.

 

[Nick1994]

A mechanic needs to go over it and look for a leak.

My mom's Buick Rendezvous one day had no brake pressure and it turned out the bolt that bolts the hose to the RR caliper came loose, tightened it and 3 years later it's still fine. Could be something that simple.

Could also be the master cylinder/ brake booster leaking fluid into the cab making it so you can't see it.

 

[Trav]

The master cylinder could have an internal leak into the booster, in time this will destroy the boosters diaphragm.

 

[Rick in PA]

Originally Posted By: Trav
The master cylinder could have an internal leak into the booster, in time this will destroy the boosters diaphragm.


I was wondering about that. Could then the brake fluid be drawn into the engine intake system and burned, thus, no puddles or evidence of leakage?

OP, tell your buddy, for all of us, he needs to get it fixed.

 

[Wolf359]

I'd also guess wheel cylinder in the rear brakes. You probably wouldn't see fluid if it's a small leak, but once you take the drums off, it might be coated with fluid. I think there are still a few shops out there that will do free brake estimates. Have him take it to one of those shops and once they take the rear drums off, you'll know if everything is good back there or not.

 

[zzyzzx]

It's not a mystery, you haven't looked hard enough. It just doesn't disappear, it's going someplace.

 

[NHGUY]

Friends don't let friends drive (or ride in) a Cobalt...particulary one with bad brakes.

 

[Quest]

peeking through the wheels RE: front caliper leaks doesn't cut it.

In fact, you must jack up all 4s, slightly press on each caliper/wheel cylinder dust boots to check for wetness/leaks.

Also: don't discount the possibility of master cylinder leaks, for many a times, unless you unbolt the master cylinder from vacuum booster drum, the leak will accumulate in the drum diaphram cavity before you notice it.

A leak is a leak is a leak. brake fluid in a hydraulic braking system doesn't simply gone missing/disappear.

Q.

 

[dishdude]

Originally Posted By: NHGUY
Friends don't let friends drive (or ride in) a Cobalt...particulary one with bad brakes.


That's right, everyone should drive an '88 Aries K.

 

[Trav]

Originally Posted By: Rick in PA
Originally Posted By: Trav
The master cylinder could have an internal leak into the booster, in time this will destroy the boosters diaphragm.


I was wondering about that. Could then the brake fluid be drawn into the engine intake system and burned, thus, no puddles or evidence of leakage?

OP, tell your buddy, for all of us, he needs to get it fixed.


Depending on the booster type and vacuum location it could but on most it just pools in the bottom of the booster.

 

[Lubener]

Originally Posted By: Trav
The master cylinder could have an internal leak into the booster, in time this will destroy the boosters diaphragm.


You can go one step farther, remove the M.C. and move it slightly away from the booster(leave lines connected) and check for wetness and/or rust behind the M.C. The fluid attracts moisture and rust develops where there is fluid. Also check for leaky wheel cylinders on rears.

 

[Trav]

That's a given, how else are you going to check it without looking.

 

[Rand]

My vote is for rear wheel cylinders first. Those things seem to get unreliable after 10 years or so.. esp if neglected and the shoes disintegrate.

They can also hide small leaks.


If not I'd dig into the MC as suggested.