Blame mother nature!!...
My trucks have all been having "grabby rear brake" syndrome since the monsoon season started 2 months ago--seems like the rear drums rust up when sitting overnight in damp humid conditions,and the first time I hit the brakes when leaving my driveway,no matter how lightly I apply the brakes,the rear wheels chatter and lock up instantly..after few stops,everything is normal again!..I've pulled the drums off to make sure no gear oil was on the shoes,but they were dry,and had plenty of meat on them..
Your front brake woes are probably due to the weather too..rotors rust instantly overnight,and the rust gets imbedded into the pads..maybe the shims (if any) wore thru on that side,and is letting vibrations from the pads get transferred to the calipers..I use "Disc Brake Quiet" paste on the back of the pads,to glue them to the caliper and its piston..I've used several layers of duct tape in a pinch,and I think it works as good as the disc brake goop!.
