Could be old hard pads. Disc may have grooves/slight warping. If you end up replacing the pads, make sure pistons don't have crud on them before you push them back in the caliper. Otherwise you have a recipe for sticking calipers.

Bert

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'70 111 280SE/c 3.5 (4 spd manual) - sold
'63 MGB
'73 MGBGT V8