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Brake pedal travels 2 inches before brake acts with spongy feel. Is it related to the power booster?

Tiny
DANIELO
  • MEMBER
  • 2000 MERCEDES BENZ CLK430
  • 35,000 MILES
I have changed the pads, the master cilynder, the dot 5 brake fluid and I am sure that that there is no leaks or air in the system. But, I feel a very spongy pedal that travels a lot before the brake acts. The effort to brake increased just a little bit. However, once in the end, the brake stop power is still good.
I also own an E class 1994 420 and the brake feel is much better. It seems that for my clk 430 the brake is lazy to start acting and too spongy and unprecise.
Do you think it could be related to internal diaphragm problem in the power booster? I have heard that for some power boosters, before the brake become trully hard and difficult, it could be spongy and quiet lazy once only one internal part is damage. For a common person who not rum the car daily it could be almost normal.
What do you advise me. I really feel that the brake is not normal. Thank you a lot.
Daniel
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Thursday, November 3rd, 2011 AT 12:04 AM

3 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,747 POSTS
Was the master cylinder push rod adjustable? Are the rear brakes properly adjusted? Did you check the rubber brake hoses to make sure they are not expanding?
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Thursday, November 3rd, 2011 AT 1:17 AM
Tiny
DANIELO
  • MEMBER
  • 2 POSTS
Hello, the master cylinder is adjustable, but the mechanic who changed assured that it is correctly installed. The fluid is new, the brake rotors and pads were ok in the parameters and adjusted. The mechanic also said that the brake hoses were fine.
They say that for the 2000 clk 430 is normal to have a spongy and low pedal. But, I do not agree once the effort to brake is incrising with time.
Is there any test that can be made with the power booster or the manifold hose? In order to check if they were fine. Even after changing the master cylinder, the fluid and the pads, I did not feel any difference.
The overall car condition is optimal. Low milage, only one pre-onwner and engine is fine. No malfunction is detected in the scanner. I will be waiting for your reply.
Thank you a lot.
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Thursday, November 3rd, 2011 AT 12:41 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,747 POSTS
I feel the push rod for the master cylinder is the issue. The pedal should not be 2 inches from the floor and spongy. If he isn't a Mercedes mechanic, I would have someone adjust it for you. It will give you a solid pedal that doesn't go to the floor.
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Thursday, November 3rd, 2011 AT 4:42 PM

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