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1985 300SD
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26 Posts
Discussion Starter #1
I had the master cylinder replaced back in the fall . At that time they said also that the booster needed replacing now or at some point in the near future. Being on a budget I opted for the latter.Well , the other day the Brake (red light, like when the Parking Brake is engaged) light came on and has stayed on . I checked the fluid and all looks good , but there appears to be two chambers to the fluid reservoir . And one is low and I don't seem to have access to that chamber . I'm not sure where to start with all of this .
 

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1991 500SEC sub 50K mi. 1987 560SEC Now 150K mi. 2018
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4,292 Posts
Hi 4am,

The light is on probably due to the low fluid level in one of the chambers, as you've noticed.

This can be due to several reasons, not the least of which is a leak. Have the car checked out, as you've got a real safety issue with the car right now. If no visible leaks are present, I would tend to suspect the brake master cylinder is leaking into the booster.

You can put more of the correct grade of brake fluid in, but that won't address the root cause, which absolutely needs attention.

A couple of offerings from the CDs for you.

Regards, MBL
 

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1985 300SD
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26 Posts
Discussion Starter #4
But did you read , I just replaced the MAster Cylinder back in the fall . They said it was the booster that may go next . Thanks for the reply and info . Any more would be welcomed . Spence
 

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Depends on the day!
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just keep adding to the front, it will bleed into the rear chamber. I would check your calipers, the rears have a bit of a pention for leaking at times.

Jonathan
 

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1985 300SD
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Discussion Starter #6
I tried all the above mentioned suggestions and I still have mushy breaks . So we have a serious problem . I'm waiting on my mechanic to call me so he can take a look at it . Thanks for the hints guy's . My poor baby is on her last leg anyhow , she's got 324,000 and a previous neglectful owner . I bought her as cheap transportation at the moment , fell in love and hope to find another 300SD in mint someday .
 

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'83 280SE (Daily Driver), '84 380SE (Donor/ Parts)
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I tried all the above mentioned suggestions and I still have mushy breaks . So we have a serious problem . I'm waiting on my mechanic to call me so he can take a look at it . Thanks for the hints guy's . My poor baby is on her last leg anyhow , she's got 324,000 and a previous neglectful owner . I bought her as cheap transportation at the moment , fell in love and hope to find another 300SD in mint someday .
don't mean to drag up an old topic, i too have mushy brakes in my '83 280se.
I bled them TWICE, once last weekend (flushed old fluid out) and again this morn but the brakes are still mushy.
If i stand on the brakes hard from ~80kph, the rears lock up slightly but i would expect all 4 to either lock up or at least slow me down reasonably quickly, which is doesn't.
I have replaced the front rotors and pads, the rears are still ok as the pads were done around 6 months ago by a so called mercedes service agent who i asked specifically to "assess and repair complete braking system..." i got it back from them and honestly couldn't feel any difference. I'm not going back there again... the front rotors were WAY past due for replacement and they did and said nothing about them... grrr

i have a donor 380se so if the master cylinder or booster is knackered i could swap em out.
But i want to confirm before i go about that as it looks to be quite a task...

opinions, suggestions?
 

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from small to large
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Focus on master cylinder. Although you changed it not long ago, it may just be a defect. Years ago when my brake fluid level kept getting lower and lower, I was wondering the same, eventually after I opened it up I found out the fluid all went to the booster chamber. Replacing master cylinder is an easy part. Remember to do bleeding afterward.
 
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