What is the BEST WAY to change brake fluid?

[TheEngineer]

I’m looking at the brake fluid: It looks dirty. But I have an invoice from my friendly MB dealer for replacing the vacuum assist unit. That cost of several hundred dollars. Wouldn’t you think they’d replaced the brake fluid at that time? I have a suction cannister, normally used to change engine oil. If I suck out the old brake fluid via a bleed nipple, and keep the reservoir full with new brake fluid, is that the best way to change?

1969 280SL,Signal Red, A/T, P/S, A/C, Both tops.    Ret. engr. 1967 230SL - Sold

[Joe]

No, that's not the best way. You have to both get the old fluid out of all of the lines, and also evacuate any air in the lines. This cannot be done by sucking fluid out of the reservoir.
To do it, you have to put new fluid in the reservoir and then get it to circulate through the lines, replacing the old fluid as it goes from the reservoir to the individual wheel cylinders or calipers. If you look at the archives for brake bleeding, you'll surely find topics on this popular subject.
Joe2

[Bob G ✝︎]

Good subject and one I have had to dela with on my wife's 300E Sportline when we first purchased it. The brake fluid was dirty and so I purchased from Griots a manual pump vacuum bleeder, worst tool I ever had my friend happen to have a Motive power bleeder . You fill the tank with fresh clean brake fluid pump it up to 15 PSI attach the special resivor cap for Mercedes Brake resivors and bleed the brakes as if one is in side the car steeping on the bake pedal. The entire proceeder took use 30 minutes.
Best tool I ever got. see www.motiveproducts.com

Bob Geco

[rwmastel]

Joe,
Read the engineer's post again.  He said, "If I suck out the old brake fluid via a bleed nipple..."

Engineer,
You are on the right track.  Many people bleed the fluid through pressure (of vaccum in your case) instead of pressing the pedal.  I use a tool similar to what Bob Geco described.  It has a canister for the fresh fluid that you connect to the brake resivoir via a special cap with connecting hose.  The canister also connects to a tire.  The air pressure from the tire goes into the canister and it pushes the fluid from there into the brake system.  Just open the bleeder valves (right rear, left rear, right front, then left front) one at a time and refill canister as necessary.

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420