So after swapping the calipers on my '90 240 DL Sedan I decided I should figure out if there was a real problem in the first place. First, the history:

I got the car with a spongy brake pedal that rapidly progressed to a sinking brake pedal.

The car had multiple signs of neglect.

Left front rotor had uneven rust that did not get scrubbed off.

Replaced the master cylinder with rebuilt (later proven to be possibly a poor rebuild).

Pedal no longer went to the floor but still spongy.

Did an attempt at a bleed and full fluid replacement but broke the upper bleeder off the passenger front caliper.

Spongy pedal no better. At least 3" of travel before significant braking.

Replaced both front calipers and rotors with virtual new units from the PnP today.

Braking almost normal after various fun malfunctions trying to bleed.

Removed calipers have full travel of the pistons with channel locks and air pressure. Pads are unevenly worn...inner on the passenger side and outer on the driver side much thinner that their companions.

Since I live in the rust belt my guess would be that the thinner pads had at least one piston that was hanging due to rusting of the "ways" as Art calls them. Alternate explination, one chamber of the MC is not effective and mannifests itself by applying the pad on the side that has an effective piston first.

Your thought?

Mike