It's a farm truck, lumber getter trailer puller. Not driven often, after sitting for awhile the brakes seem to be pulsing in front like antilock, as if braking on ice. I checked both front caliper springs or plunger slides and they are free not froze up. Any suggestions?

 

Most often the brake discs take on a coating of rust everywhere but under the caliper pads.
When you apply the brakes , the coefficient of friction is altered until it gets worn off.
Good luck.