Brake pedal has suddenly become soft

STEMLINE

MEMBER
1999 MERCEDES BENZ SL500
6 CYL
TURBO
2WD
AUTOMATIC
55,000 MILES

I just had the brake fluid changed, as Mercedes recommends, and now I have to push the pedal down much futher to engage the brakes. I thought there might be air in the lines, but my mechanic assures me there is not. Also, the Check Engine light comes on. My mechanic thinks I need a new master cylinder; this doesn't seem likely to me, given the mileage and the recent sequence of events. What to you think is wrong?

3 Replies

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Since you just had the fluid replaced, it does sound like there could be air in the system. However, even though it only has 55K on it, it is 15 years old. The MC could be bad. Tell me this. I need you to start the vehicle and apply the brakes. Keep your foot on the brake at a steady pressure. Does the pedal slowly make its way to the floor?

As far as the check engine light, have the computer scanned for trouble codes. That will help me determine what possible problems there are.

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Saturday, August 16th, 2014 AT 5:16 PM

STEMLINE

MEMBER
5 POSTS

I didn't hope to get an answer so soon! The car is at my mechanic's, who, quite reasonably, is not open today. When I see him tomorrow, I will try the test you recommend and let you know what happens. Thank you for your quick response!

Dave

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Sunday, August 17th, 2014 AT 3:11 PM

STEMLINE

MEMBER
5 POSTS

When I press on the pedal, it does not go quite all the way to the floor.
When I pump the pedal, it goes down to about the same point. It hisses with each pump; sounds sort of like air brakes.

Hope this helps. When I was fixing cars (I worked a lot on my '43 3-window Ford coupe, as it kept blowing first gear), they were VERY MUCH simpler. NOw I wouldn't consider trying to work on anything.

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Monday, August 18th, 2014 AT 3:17 PM