I'm with Eric on this one. I believe it's the master cylinder. I had this happen on a 190E I had. I would have to get out and loosen a line (for the front brakes) from the master cylinder to relieve the pressure. The master cylinder was not releasing pressure in the line after you let your foot off the brake.

It would build up on me and got worse over a week or so. Replacing the master cylinder fixed it for me. I went through a lot of brake pad too. If it sat for a while, it would eventually bleed back.

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Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)