W203 sinking brake pedal

[robparker]

I just acquired a low mileage c270 that's been sat around.
Brakes were spongy when I got it, and I've just replaced pipes and discs/pads and manually bled it (getting no air coming out).
Engine off, pedal perfect.
Engine on, pedal good, but then continues to sink slowly to the floor.
Since changed the master cylinder and abs pump just to see. No difference. 99.9% sure there are no leaks anywhere.
Would pressure bleeding make a difference? I can't think what else to try.
Thanks

 

[Bellow]

Did you bench bleed the MC before fitting?
Did you cycle the ABS valves during bleeding?

 

[OneForTheRoad]

I just acquired a low mileage c270 that's been sat around.
Brakes were spongy when I got it, and I've just replaced pipes and discs/pads and manually bled it (getting no air coming out).
Engine off, pedal perfect.
Engine on, pedal good, but then continues to sink slowly to the floor.
Since changed the master cylinder and abs pump just to see. No difference. 99.9% sure there are no leaks anywhere.
Would pressure bleeding make a difference? I can't think what else to try.
Thanks

It's worth a try . Just make sure the engine is off .

 

[rf065]

Engine off, pedal perfect.
Engine on, pedal good, but then continues to sink slowly to the floor.

My CLK220 was exactly the same, nothing wrong with it, it's a diesel thing to do with using a vacuum pump to the servo when the engine is running.

 

[Petrol Pete]

Vaccuum leak effecting the operation of the brake servo.

 

[BlackC55]

Pressure bleed with pumping pedal usually sorts these.

 

[robparker]

Just bought a manual pressure bleeder, before my friend brings his electric workshop one, got a bunch of air out of the abs pump, made no difference at all unfortunately.

 

[robparker]

My CLK220 was exactly the same, nothing wrong with it, it's a diesel thing to do with using a vacuum pump to the servo when the engine is running.

Definitely not normal!

 

[robparker]

Vaccuum leak effecting the operation of the brake servo.

Interesting thought.... Could be the servo I guess. I feel it must be air really though

 

[rf065]

Definitely not normal!

Well the brakes worked perfectly over 150,000 miles, so whats the problem?

 

[robparker]

You drove 150,000 miles with a pedal that crept to the floor? That's fair enough, but it's not for me!

 

[rf065]

You drove 150,000 miles with a pedal that crept to the floor? That's fair enough, but it's not for me!

But it doesn't creep to the floor unless you sit stationary and keep pressing it. If you stop doing that it works perfectly.

 

[Stratman]

If the pedal goes to the floor the question has to be, "Where does the fluid go?"

 

[Petrol Pete]

To view this content we will need your consent to set third party cookies.
For more detailed information, see our cookies page.

Accept third party cookies

 

[robparker]

Update..

Nothing has worked, multiple pressure bleeds, 3x master cylinders, asb pump, no leaks...

I'm taking it to a specialist now, if they manage to fix it I'll update, if not, scrap time. Shame for a minter really if it comes to that.

 

[Bellow]

Did you bench bleed the MC before fitting?
Did you cycle the ABS valves during bleeding?