Pull all the pads and take a small wire brush and remove all the crud in the slots where the pads fit. Get them shiny clean.

Apply a SMALL amount of antiseize (any brand) to the sides of the backing plate and the back of the pad where the piston contacts mbefore re-isntalling. OEM pads will have a ring or a coating of dense plastic here, aftermarkets are usually plain steel (hint hint).

Remove brake fluid reservior cap and push the brake pistons back in each caliper a bit. If they don't move smoothly with minimal pressure, you need to rebuild them. If they do, open the bleeder valve, attach a hose, and press them all they way back, then close the bleeder. Use an old turkey baster and remove all the old brake fluid from the master cylinder, replace with fresh, and flush the old stuff out by bleeding after you re-install the pads.

The leading causes of brake squeal on an 80's MB are 1) aftermarket pads with no brake paste (or in some cases with), 2) dirty calipers so the pads sit crooked or bind, and 3) sticking calipers.

By this time, it's likely the piston seals in the calipers are rock hard, meaning high hard pedal, squeals, drag, etc. Rebuilds are easy, and it's most likely time for new brake fluid anyway.

Break in new pads with very gentle use until the "fur" wears off and you have full pad to rotor contact, and sandpaper new rotors to remove machining marks, else they groan.

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!