93 explorer brake problem

my 93 explorer has recently developed an annoying problem. the brakes when cold work well with no noise or vibration when stopping but after about 20 minutes of driving and braking ,when the vehicle is almost stopped there will be what is best described as a loud dull chirp and at the same time the pedal will sink a bit. it sounds that it is coming from the front left. i pulled off the wheel , inspected the pads[ they were fine] and lubricated the sliders with no change. i am leaning toward a caliper or possibly the a.b.s. so any advice or ideas or much appreciated as i do not wish to just keep replacing until i find the problem i should also mention that this always occurs after some driving and braking, always when almost stopped and with no pulling to either side thanks sam

Chances are pretty good this is primarily due to the pad composition. There may be a particle in the compound that is a bit too hard. Before replacing the pads you could try a few things.

First, inspect the inner and outer diameters of the braking surfaces to see if there is a ridge that is polished from the brake pads. If so, that could be contributing to the noise. You can either get a rotor resurfacing kit that runs in a drill and basically uses a spinning Scotch-Brite pad to knock down the edges and remove any glaze on the braking surface. You could also have the rotors machines lightly to remove the edges and provide a new braking surface.

Another thing you could try would be to use a bench grinder to chamfer the leading and trailing edges of the brake pads if they are not already chamfered.

You could try swapping the pads from right to left as well.

You also should check the rear brakes, even though you think the noise is coming from the front. If you have a wheel cylinder (assuming drum rear brakes) that is contaminating the shoes, that could cause a "dull chirp" noise. You could also have a leaking axle grease seal that is contaminating the braking surfaces as well.

-Rod