You don't have to remove the calipers to get the pads off- just use a set of channel locks to squeeze the old pads away from the rotor and they will just slide out (after removing the pins, of course).

When was the last time you did a brake job? If you don't know, I would replace all four. It is really up to you, though, and how much you want to put at risk.

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Andrew

1989 Volvo 745- 202K