So some months ago i picked up a fery clean 98 e300. Had some other issues that were more pressing. When i looked at it, it had a very soft to the floor brake pedal. But the brakes did kinda sorta work. Was low on my list and asked the seller. Told me he swapped pads and used a c clamp like usual to compress the piston. Afterwards the pedal was aweful. Well once i finally started working on the brakes i looked up the procedure. Says that it required a power bleeder at 2bar to unseat the abs check valves. Conventional methods could damage the master. So i hooked up the motive bleeder and worked my way around. Got the fronts to spit, rears remained a dribble. Also noticed the rear fluid was really dark and back part of the master was dark. End result brakes were better but pedal still drifted.

Decided to replace the master with a TRW master, bench bleed first and installed. Got a better look at the rear circuit. Had some sort of sludge or really dirty. This time had my pops in car, set the bleeder to 2 bar. Had him pump along with bleeder. Rock hard pedal. Again the rears spit a little tiny bit, if i had him pump under pressure nothing spectactular. The fronts, with the bleeder open under pressure every pump was halthy stream. After a while i notice i had frozen rear calpier. After finished had a so so pedal, that would go nice and hard with a second pump.

Next step was today, replaced both rear calipers. Bleed the brakes under pressure key off, key on engine off and engine running. This time after many pumps i could get the rear to spit one time then dribble. The fronts stayed working as they did.

Took it for a test drive, firm pedal with emergency stop. A normal planned stop pedal firms up after about 20% of throw. Rock hard after a double pump. Low speed driving, soft press and goes down.

After reading some various stuff and talking to mercedes tech. One article said had to activate the abs with scanner. Saw another saying similar problem had crap in the abs circuit. Mercedes tech said only use oemmaster cylinders and he never had an issue like this. I was thinking maybe the rear hoses are coming aprt inside after 195K?

Any one have any input.

I have bled my old w124 using a pressire bleeder but not my w210, but I have to question why you are still pumping the pedal when using pressure bleeder? surely just open relevant bleed nipple and let fluid out.
Can the master cylinder seals be damaged by pumping pedal when oressure bleeder in use anyone ?

after talking to some other people, i'm leaning towards collapsing rubber lines going to the calipers.

I've "heard" about collapsing lines but never experienced them. I change hoses the 1st time I deal with brakes on a new car unless the hoses look new and are completely uncracked.

Soft pedal for me has always been air or a faulty master. One SD seemed to have soft brakes when the car was on stands. It had 2 quarts of fluid run through it with new calipers, hoses, pads & MC. I got tired of messing with it, took it off the stands and it drives fine. I can't explain the soft feeling but it was immediately perfect once on the ground.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Bleeding might be more involved if the car has ESP. Does the button ahead of the driver power window switch say ASR OFF or ESP OFF?

Sixto
98 E320s sedan and wagon

it does, but again with the 29 psi on the master it is "supposed" to unseat the check valves for that. I'll keep updated, if i replace the hoses and that clears then good. Otherwise I ordered a 38 pin com connector several weeks ago to use the scan tool on the car.

Success!!! Replaced the rear lines and was actually able to bleed the rears. Pedal was better but still a little soft. Since its raining here today I took it down a seldom area and stood on the pedal at 35mph. Abs went crazy but could only feel one channel. So I went ahead and repeated 4 or 5 more times. Each time the pulsing was stronger. Finally after the last I had an excellent firm pedal.