If the pads are in good shape, I would just change out the sensor. At $2.85 for each side http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1WG0P2UAL1WW02P7CX&year=1979&make=MB&model=240-D-002&category=N&part=Brake+Pad+Sensor I don't see where you could go wrong.

Most of the stopping power comes from the front brakes. Were the front rotors cross-drilled also?

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Sam

84 300SD 350K+ miles ( Blue Belle )