When installing pads (best to use OEM ones from Padgid, Textar, etc), always clean the slots in the calipers completely of rust, corrosion, or old brake dust. Otherwise, one side can be tighter than the other, allowing the pad to vibrate.

Also, coat the piston contact area, the sides of the backing plate where it touches the caliper, and the spring where the retaining pins sit with some antisieze. This will prevent a large amount of squeal.

Breaking is required, and the brakes will be somewhat less effective when initially applied. Fur on the surface from machining, I think.

To fix your problem now, pull the rear pads and apply the antisieze, and take some coarse sandpaper and rough up the contact face of the pads. Re-install and do the break-in again.

If you are using PBR Metalmasters, either change them to OEM or live with the screech, if they squeal on your car, they will always.

Note that the lastest models, mostly C class, from MB have a known problem with squealing rear brakes -- no solution yet, as even new calipers won't always fix it.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!