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Old 11-02-2007, 12:59 AM
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Join Date: Aug 2007
Posts: 28
'83 300SD - Brake Light Mystery

Hi there,

On my '83 300SD 320k miles, the brake light flickers on and off, mostly on. I tried topping off the fluid, but that made the light stay on. I took some out back to the line marker for full and now the light again flickers on and off, mostly on.

Now the mystery... on the brake fluid reservoir, there are two electrical connections to two thing-a-ma-bobs (sensors?) that have what looks like a rubber cover on them. I can spin the rubber cover or mash down on it. I can not find a way to remove the covers. However, after mashing on them, I noticed that the light is no longer lit unless I have the emergency set. Take emergency off, light goes out - i.e. works properly.

But, after a few drives, the light resumes its flickering on and off, mostly on. I can get it off for a bit by simply mashing on the cover. I did nail it down to just the cover closest to the cabin firewall. Why does mashing the cover make the light go out for a while and what can I do to get it working completely without the mashing?



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Old 11-02-2007, 01:12 AM
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Join Date: Jan 2002
Posts: 18,355
Aren't there two reservoirs with one filling from the other? Is the back reservoir low causing the light to come on?
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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Old 11-02-2007, 01:43 AM
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Join Date: Oct 2004
Location: Grand Rapids, MI
Posts: 15,098
I bet you are losing brake fluid. Have you looked under the car for rusty lines?

Those rubber "buttons" pull off, they're just a rubber cap. They can (and should) be replaced when they get cracked or dried out. Don't try to powerbleed without new ones on there! Fluid will go everywhere!

The light comes on on the dash when the floats in the reservoir are I bet you are losing fluid, especially since it happens "after a few drives", and its probably the rear brakes, or else you'd really notice it. We had the line going to the rear of one of our cars rust out, and it drooled fluid when the brakes were pressed.
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 83k - mine - (OC-85,500)
'17 Metris(VITO!) - 13k - wifes (OC-17k)
'01 E320 Wagon - 159k - mine (OC-160,000)
'01 E320 - 179k - dad's (OC-182,500)
'07 E350 Wagon - 131k - dad's (OC-132,500)
'01 SL500 - 51k - dad's (OC-52,000)
'16 E400 4matic Sedan - 57k - Brothers (OC-64,000)
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Old 11-02-2007, 08:06 AM
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Join Date: Aug 2007
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I have had the car for 4 months, and have yet to have to add fluid. Qty was always at the full line since day one. I added to top off only to see if it made the light go out - which it did not, only made the problem worse. Caps seem to be in good condition and mashing them does not produce any fluid anywhere. So, I am not losing fluid. It seems to me that it is simply that one sensor is somehow flaky.
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Old 11-02-2007, 08:14 AM
toomany MBZ's Avatar
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Location: central Va
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There are two brake lights in the dash, the yellow/orange circle with wavy lines, flickering means the wear sensor on the pads are letting you know it's time to replace pads. The red parking brake light flickering means a low fluid level condition.
83 SD

84 CD
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Old 11-02-2007, 08:47 AM
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Join Date: Sep 2006
Location: MA
Posts: 523
E-brake pedal not coming all the way back?

I had to add a spring at the pedal to keep my light from coming on.

Mark in MA
05 MB E320CDI 358k Granite Grey Metallic
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99 Dodge 2500 Cummins 5sp 144k
83 MB 300SD 354k
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