The Mystery of the Disappearing DOT 4...

[Hit Man X]

Okay gang, my SD is roadworthy... sorta. I have recently finished rebuilding the brake system from front to back.

Reman master cylinder
Reman front calipers
New front rotors
New front pads
New front lines
New front bearings
Reman rear calipers
New rear rotors
New rear pads
New rear lines
New rear bearings
New rear e-brake shoes

BUT -

I drove for a few days and lost almost all of the brake fluid in the reservoir. The odd part, no puddles showing that loss of fluid. Only thing I can think of is that the fluid from the MC is getting into the booster, then from the booster down the vac line to the vac pump?

[AdvisorGuy]

Sounds like a good possibility. Unbolt the master & pull it forward a bit..

[patbob]

Originally Posted by Hit Man X

I drove for a few days and lost almost all of the brake fluid in the reservoir. The odd part, no puddles showing that loss of fluid. Only thing I can think of is that the fluid from the MC is getting into the booster, then from the booster down the vac line to the vac pump?

Check the hard lines for leaks, especially if its a rust belt car. Check the bulb for the brake idiot light to make sure it isn't burned out and unable to tell you something.

Not an MB, but my mom had the hard brake lines on her car rust away and give out one summer. There was a loss of a squirt of brake fluid at every stop, but no loss while parked, so it took us a while to figure out what had happened. Sensor must have failed too (or my mom ignored the brake idiot light until the bulb burnt out) because the idiot light wasn't going on either.

[tangofox007]

Originally Posted by patbob

Check the bulb for the brake idiot light to make sure it isn't burned out and unable to tell you something.

What's it going to tell him that he doesn't already know?

[pawoSD]

Originally Posted by tangofox007

What's it going to tell him that he doesn't already know?

True, but its still good to have that light working.

I will assume this is a new issue and not the reason you replaced the entire system...that said I would check the following areas.
1) The M/C as stated above. I have seen my fair share that have leaked into the booster. The brake fluid will also destroy the baffles in the booster as well as any lines they are pulled through.
2) Along the lines (no pun intended) of the leaky hard lines, I seriously doubt this of the hard lines but would check all connections of flex lines you had replaced. If they are leaking it will be as patbob stated, that is it will squirt out during braking and not leave puddles. Of course you should see some evidence of this somewhere.

[mobetta]

If you pump the brakes in the driveway, you will see puddles if any lines/ calipers leak.

reman calipers- I got cardones from checker and they didnt last 4 weeks- look careful at them any leaks will show on the inside of the wheel/tire...

[whunter]

Originally Posted by Hit Man X

Okay gang, my SD is roadworthy... sorta. I have recently finished rebuilding the brake system from front to back.

Reman master cylinder
Reman front calipers
New front rotors
New front pads
New front lines
New front bearings
Reman rear calipers
New rear rotors
New rear pads
New rear lines
New rear bearings
New rear e-brake shoes

BUT -

I drove for a few days and lost almost all of the brake fluid in the reservoir. The odd part, no puddles showing that loss of fluid. Only thing I can think of is that the fluid from the MC is getting into the booster, then from the booster down the vac line to the vac pump?

From the vacuum pump into the engine oil pan.

[Johnhef]

If its in the booster there will still be some in there, pull the MC forward and take a look/stuff a rag down in there and see if it gets wet.

[Hit Man X]

I rebuilt the system as it was due, fronts have been done for many months now (and working fine), then did the MC as it dragged in the past. Rears were like fronts, needed to be done. Dust boots torn, calipers grooved, etc.

I had a helper pump the brakes while it was on ramps (both axles) I could not see evidence of seepage/squirting anywhere. Also I had my pressure bleeder on there, nothing to be seen.

It's a Texas car (has been entire life) so the loss is odd. I traced the hard lines to the rear and they're sound. Same with the front. The only one I could not see easily was the passenger side.

I run PILES of the Cardone calipers, very few fail for me.



So if MC did leak into booster, would I need to pull booster to drain? Oil change too (I just changed it )?

[Hit Man X]

New MC in, will flush/bleed in the afternoon and report back.



Guess I should go ahead and rechange my motor oil?

[pawoSD]

Originally Posted by Hit Man X

Guess I should go ahead and rechange my motor oil?

That would probably be a good idea, as its essentially the only place the brake fluid could have gone (other than sitting in the booster). Depends how much went into the booster.

[Hit Man X]

0.5-0.75 of a quart.

[pawoSD]

Thats quite a bit, I'd probably do the oil change just to be sure, never know if any got sucked into the engine. Not worth risking damage to a nice 603 engine.

[patbob]

Originally Posted by tangofox007

What's it going to tell him that he doesn't already know?

Sorry.. didn't followup with the thread.

Don't know MB specifically, but on every car I've ever worked on, the brake system was divided into two zones that each consisted of opposite corners of the car. Among other things, the sensor that lights the light checks that both zones have equal pressure.

So.. if one zone leaks, there should be a difference in pressure and the light should illuminate every time you press the brake pedal. It is a useful diagnostic if you suspect a leak, but it can fail too, the most common failure being that the indicator bulb burns out.