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  #1  
Old 08-15-2002, 09:45 PM
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Join Date: Mar 2001
Location: Schenectady, new york
Posts: 229
brake bleeding nightmare '86 300SDL

I have bleed automobile braking systems all my life, sucessfully I might add. I changed brake pads on my '86 300SDL all four wheels, never opening the system. After finishing I tried the brakes, fully expecting the first pedal depression would go to flooras it had on all the other I had ever changed pads on. Brake pedal never pumped back up? I decided to bleed all four wheel calipers starting at the right rear, then left rear, no problems so far, then I proceeded to the right front, no air, no brake fluid, left front same thing. I then bought a device that forces fluid into the brake reservoir @ up to 20# pressure, again no air, no fluid, nothing at all. I tried bleeding the brakes in the traditional manner, have a helper depress the brake pedal, open the bleeder valve, close bleeder valve have helper let off, repeat 50 times. All this with the positive pressure device still attached to the reservoir. Anybody have any ideas as to what the heck is going on here?

'86 300SDL 165,000
'87 560SEL 135,000
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jcciem
'94 SL5000 60,000
'91 350SDL 545,000
'91 350SD 197,000
'00 E55 AMG 77,000
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  #2  
Old 08-16-2002, 01:53 AM
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Join Date: Oct 2001
Location: Newton, MS
Posts: 123
I would first suspect a rubber hose failure on the inside. If you think they may be original, they are overdue for replacement. They are known to fail in the other direction also and prevent fluid from returning, thereby keeping the brakes applied.

BTW, the old fashion way off pumping up pressure with the pedal can cause problems. The inside pressure cup is forced to travel outside its normal range and encounter less than smooth surfaces.

Harry
86 300 SDL
85 300D Euro
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  #3  
Old 08-16-2002, 01:58 AM
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Join Date: Feb 2000
Location: seattle, wa
Posts: 87
I've blown out many a master cylinder by depressing the caliper to fit the new pads in thus creating back pressure that can defunk the master cylinder. I always open the bleeder on the caliper while depressing. This saves me the hassle of explaining to the customer wy they need a new master cylinder when they came in for a routine pad change. If you close the bleeder while depressing just before you get to the end of the travel there's no need to bleed the system.
paul
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  #4  
Old 08-16-2002, 10:50 AM
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Join Date: Jun 2000
Location: Plano, TX
Posts: 2,503
This could be really simple. You have fill the reservoir __way__ up to the top before any fluid overflows into the back chamber, which feeds the rear calipers. About 90% of the volume of the reservoir is dedicated to the front brakes - only the extreme rear bit is divided off for the rear brakes. Take a strong light and make certain you have fluid in the section for the rear brakes. When bleeding it only takes 5-6 pedal strokes to empty the portion of the reservoir for the rear brakes, so it's easy to get air into the system.

Hope this is your problem, and don't ask how I learned this...
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  #5  
Old 08-16-2002, 11:44 AM
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Join Date: Oct 2001
Location: Newton, MS
Posts: 123
Paul

Great idea, I've never opened the bleeders like that, but I sure will from now on.

Thanks

Harry
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  #6  
Old 08-27-2002, 12:12 AM
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Join Date: Mar 2001
Location: Schenectady, new york
Posts: 229
it was a defective master cylinder i replaced it and it's all repaired
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jcciem
'94 SL5000 60,000
'91 350SDL 545,000
'91 350SD 197,000
'00 E55 AMG 77,000
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