The left rear brake hose failed on the 300SD.
I changed it and have bled the system until I am "blue in the face" and can not get the brake system to operate properly.
Now it will pump up and then go to the floor, as before it would just go the the floor because fluid was leaking out.
I have bled all 4 wheels, starting with the RR, LR, RF, LF and still I can not get it. I have used over a bottle of fluid.
What is the secret? or are there other issues I am not finding?

Thanks
Doug

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83 300SD Dark Silver Dark brown inside

I am not quite sure what the problem is, but when I bleed the brakes I do it with another person. I pump the brake and when it builds up pressure i hold the pedal firmly and have another person release at the caliper until the foot/pedal drop to the floor and I hold the pedal there until the guy at the caliper tightens the valve again. I do that until the air is our of the system and only oil is coming out of the valve when it is released. I am not really sure what the problem is that you are describing.

I used a mighty vac. And pulled the fluid through the lines.
When you step on the pedal, it goes down and is soft. and the car takes a long time to stop. If I pump the brakes, then it gets better. Like there is air in the lines, but I get clear fluid out of it when using someone inside on the pedal to check it.
Was reading about bleeding the Master cylinder. Is this needed if the rear tank ran out of fluid. I am assuming it did because of the broken hose.

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83 300SD Dark Silver Dark brown inside

Are you filling both sections of the reservoir? I noticed on mine that the front half is filled by a small port in the main section. Unless you are aware of it, it is easy to only fill part of the tank and reintroduce air into the system.

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Sam

84 300SD 350K+ miles ( Blue Belle )

I read that the pumping to bleed takes the master cylinder past its normal range and can damage it if already worn. Do not know if it is true.

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Present
1987 300SDL
1991 300SL
1990 560SEL
2001 ML320

Past
1969 200D 1979-82
1983 300SD 1984-85
1972 250C 1982-02
1995 S350 2011
1997 S320 2012

I have filled the reservoir to the top, and bled again, With the brake pedal. Still no go.
Now I am letting it sit to see if I have air mixed in the brake fluid from all the purging.
the brake line takes a loop down, do I have to take the caliper off to remove the low spot? never had to do that before... Never had this much trouble before on amy car.

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83 300SD Dark Silver Dark brown inside

I am not really familiar with the w126 brake system, and I was not aware there was a second tank in the rear. Do you have another person to bleed the brakes with by releasing the valve on the caliper when you build the pressure by pumping the pedal? This will definitely get the air out of the system. Does the oil leak anywhere? Maybe there is another leak somewhere that is causing you to loose pressure.

It is the rear of the master cylinder tank. It looks like one, but is two.
I went out again. and no luck, but I did notice this time that the caliper on the LR has the bleed screw at the bottom. I do not think it will bleed like this, because air is trapped in behind the piston? Or is this normal?

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83 300SD Dark Silver Dark brown inside

Someone previously placed the wrong caliper on the left rear wheel, or interchanged the right and left calipers. you are correct, it can"t work this way.

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1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150

If I pull it off the mount and bleed it can I use it?

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83 300SD Dark Silver Dark brown inside

That will be a bit difficult, but probably not impossible. Use a suitable block of wood between the pads to keep the pistons from popping out when the pedal is pushed. Remember, the caliper worked before the hose failed. Just not really recommended to use the wrong part in a safety system.

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1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150

Is it possible that someone replaced both rear calipers and accidentally put the calipers on the wrong wheels? Might be worth a look.

I had the same issue on my 240D until I realized the brake fluid res has two chambers in it. On the 123's the rear portion of the res feeds the from tire, and is what you see when you look into the res with the cap off. The front portion of the res supplies the rear wheels. You have to completely fill what you can see in the res before the front half of the res will fill up. Look closely and make sure you've got fluid in the front half of your fluid res.

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you can loosen the hose fitting where it connects to the caliper, and bleed that way...
look on the opposite side, are they both wrong? if so, just swap them.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

I have personal experience with this, yes it is true, it has happened to me twice.


'87 300SDL 196,000
'94 SL 500 55,000
'89 300TE 180,000
'91 350SD 193,000

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jcciem
'94 SL5000 60,000
'91 350SDL 545,000
'91 350SD 197,000
'00 E55 AMG 77,000