Brakes - occasionally not there - PeachParts Mercedes-Benz Forum

meek · #1 07-12-2011, 08:40 AM

The 90 300D (250D Turbo) has begun to develop a brake issue. 99% of the time the brakes work fine, the other 1% you hit the brake pedal and it starts to go to the floor and the car does not slow forcing a couple panic 'pumps'. Ideas? I need to have this fixed as soon ad possible for safety's sake. Thanks.

leathermang · #2 07-12-2011, 08:48 AM

First change out to new proper fluid and do proper brake bleed..
report back with results....

Mark DiSilvestro · #3 07-12-2011, 08:57 AM

Typical symptom of a failing brake master cylinder.

Happy Motoring, Mark

Stretch · #4 07-12-2011, 08:58 AM

Quote:

Originally Posted by Mark DiSilvestro

Typical symptom of a failing brake master cylinder.

Happy Motoring, Mark

X2

tangofox007 · #5 07-12-2011, 09:01 AM

Quote:

Originally Posted by Mark DiSilvestro

Typical symptom of a failing brake master cylinder.

Happy Motoring, Mark

It's also typical of boiling brake fluid. Additional background info regarding the circumstances of the failures would be helpful

Diesel911 · #6 07-12-2011, 09:11 AM

Quote:

Originally Posted by Mark DiSilvestro

Typical symptom of a failing brake master cylinder.

Happy Motoring, Mark

X3
A failing Master Cylinder is way more common than Boiling Brake Fluid.

Drive you Car a while and be careful put your hands on the Wheels, and if you can reach them the Calipers to see how hot they are getting (looking for a stuck Caliper Piston that ought to create more heat if dragging).

If they are not getting overly Hot and the Fronts compare to each other and the rears compare to each other you have no overheating issues.

Mark DiSilvestro · #7 07-12-2011, 09:16 AM

During my first freeway outing last year, I developed a sudden low brake-pedal on my 300TD due to brake fluid boiling in a seized rear caliper. But that problem didn't simply dissappear after a few 'panic-pumps', but only after several minutes when the caliper eventually cooled down enough. When I found a place to stop, I touched all the wheel-rims and the left rear was much hotter than the rest. Fixed that with replacement calipers & hoses.

Happy Motoring, Mark

tangofox007 · #8 07-12-2011, 09:58 AM

Quote:

Originally Posted by Mark DiSilvestro

During my first freeway outing last year, I developed a sudden low brake-pedal on my 300TD due to brake fluid boiling in a seized rear caliper. But that problem didn't simply dissappear after a few 'panic-pumps', but only after several minutes when the caliper eventually cooled down enough.

It would appear that you are drawing conclusions on the basis of facts not in evidence. The OP offers no information as to the time required for his problem to "disappear." He doesn't say whether or not the "panic pumps" restore braking effectiveness.

Quote:

Originally Posted by Diesel911

X3
A failing Master Cylinder is way more common than Boiling Brake Fluid.

I would agree the odds are heavily stacked in favor of the master cylinder being the culprit. But I have also seen a number of circumstances in which the "odds" change when you get "the rest of the story."

meek · #9 07-12-2011, 10:11 AM

Thanks

PaulC · #10 07-12-2011, 11:32 AM

I've had this happen to me - internal leak in master cylinder.

Mark DiSilvestro · #11 07-12-2011, 11:43 AM

Quote:

Originally Posted by tangofox007

It would appear that you are drawing conclusions on the basis of facts not in evidence. The OP offers no information as to the time required for his problem to "disappear." He doesn't say whether or not the "panic pumps" restore braking effectiveness.
I would agree the odds are heavily stacked in favor of the master cylinder being the culprit. But I have also seen a number of circumstances in which the "odds" change when you get "the rest of the story."

Not drawing any conclusions. In the absence of any further information, I mentioned a couple of possibilities - the most likely being a faulty brake master cylinder.

Happy Motoring, Mark

digieditny · #12 07-12-2011, 12:05 PM

About a month ago I had the same problem. The brake pedal would go to the floor. It only happened 3 times in total. With a week or so in between incidents. I did a brake fluid flush and bled hoping it was air or moisture in the lines. The problem came back. I had the master cylinder replaced and now I have no issue.

Listen to leathermang. He is the god of brakes!

Stretch · #13 07-12-2011, 12:24 PM

Quote:

Originally Posted by meek

Thanks

Oh come on meek!

Give us some more information just like tangofox007 asked - help us to help you.

(No additional information in the other thread either Brakes - occasionally not there)