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#1
11-08-2012, 11:59 AM
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Master Cylinder??
1983 500sl Euro.
I've read some posts here and I'm thinking I have a failing master cylinder. I am not losing any brake fluid at all. Brakes were fine but then started to get a "soft pedal". I thought they just needed bled. However, they are getting progressively worse. If I push the pedal slowly, they will just about go to the floor and it feels as if only the rear brakes are working. (car squats and can activate anti-lock) If I "pump" them quickly, I can brake normally. If I'm sitting at a light and I've "pumped" them so I have a lot of pedal, the pedal will slowly go down. I can feel when the front brakes release and only the rears are holding the car. Since I'm not losing any fluid it has to be an air leak, correct? Does this sound like typical master cylinder failure? All thoughts and experience would be greatly appreciated. Marc
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1983' SL500 euro 
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#2
11-08-2012, 01:35 PM
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The master cylinder contains two in-line pistons, one for the front circuit, and one for the rear circuit. When the piston pressure seal (the "cup") of either piston starts leaking, the leak is internal, fluid is returned to the reservoir, and the pedal bleeds down. There is no air leak, and, as you have observed, no loss of fluid.
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#3
11-08-2012, 02:03 PM
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Just looked up how that master cylinder works and I see exactly what you describe. Wish I would have done that before I took up your time. Thanks for the response.
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1983' SL500 euro
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#4
11-08-2012, 04:43 PM
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The master cylinder for an ABS equipped 500SL is a different PN than one without ABS. I went through many hours trying to fix my '84 500SL before I discovered this. I will see if I can find the correct PN.
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#5
11-09-2012, 10:52 AM
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Rowdie,
The part number I have is: 004 430 09 01. I checked this with Phil and ordered it. I hope it's correct. Would appreciate knowing if this was what you used. Thanks Marc
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1983' SL500 euro
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#6
11-09-2012, 05:59 PM
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Can't find the info. on what I ended up using. My '84 had new MC when I bought it but the brake pedal went almost to the floor. Long story short II purchased another MC which did not work either.
Try the recommended one though I think that is the PN I had no success with. Almost certain I ended up using 004 430 26 01 which is for a 380SL with ABS. Try Tom at the Classic Center if the one you receive does not work.
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#7
11-13-2012, 07:53 PM
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Rowdie,
You were correct. This is the wrong part number. Pedal just goes right to the floor. I have no brakes at all now and I checked this part with Phil before ordering. Please advise what the classic center is, web site, telephone number for Tom, etc. I appreciate the help. Marc
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1983' SL500 euro
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#8
11-13-2012, 09:21 PM
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The Classic Center is a Mercedes operation. Mercedes Club members receive a 15% discount. Contact information:
MB-USA Classic Center, Irvine CA - Benzworld.org - Mercedes-Benz Discussion Forum
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#10
11-14-2012, 04:33 PM
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I did. I had the part you suggested next day aired.
Just put it on. Still no brakes. Must be something I've missed. Do I have to bench bleed the MC? Pedal still goes right to the floor and won't pump up.
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1983' SL500 euro
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