I just put my 1993 Caprice back on the road after a 7 year break. At first the brake pedal was stiff and did not appear to have much travel but braking seemed fine. I was doing some work on it last weekend and decided to replace the fluid in the master cylinder. I emptied the reservoir, cleaned out the residue, and added fresh DOT-3 fluid.
After driving it for a few miles the brake pedal loosened up, now the pedal has normal travel and feel. I am curious why the pedal was stiff in the first place and what could have happened to restore normal braking function?
Never mind - misread your post.
You may have partially seized cylinders (assuming they are drums) on the rear brakes. That will not be very noticeable with normal driving unless they are really seized. After a drive, check to see if the center of the/a rear wheel(s) is hotter than the rest to make sure that they are not dragging. A service check of the brakes might be a wise move.
Front disc/Rear drum with ABS. Not a daily driver. When I have a chance I will try and pull one of the drums off and take a look. I truly hate working on drum brakes. A wheel cylinder goes for 5-6 dollars on the RockAuto website so I can’t complain about the cost of parts.
After you remove the rear drum push/pull sideways a little on the shoes to make sure they move freely as a set on the backing plate. If they seem stubborn apply a little brake grease to the points on the backing plate where they are designed to slide. Do that for the other side of course too. That could be part of the explanation, shoes sticking against the backing plate rather than wheel cylinders sticking. I concur with the above post that this is more likely related to the rear drum brakes than the front discs.