When a car with disk brakes is parked for an extended period, the rust pattern is different between the exposed rotor and the area under the pad.

When the brakes are exercised after non-use, this different coeffcient of friction will feel like a warped rotor.

I find this often on cars here in the Virginia Beach area that have a low usage pattern.

Sometimes you can clear the problem with use, other times you have to surface/replace the rotors.

Jim

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14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles