After some reading on the forum, I have found a lot of info regarding reasons why this
brake sticking or dragging could possibly occur. Some of the reasons given were:

Air in the system
rubber brake hoses collapsing on brake pedal withdrawal or kinked hoses.
un-greased caliper pins
old brake fluid
master cylinder leak internally
Power Booster adjustment arm restricting master cylinder spool from returning to rest
position.

Before I start replacing parts guessing at a fix I thought it would be a good idea to bring
this up for discussion with some of you more experienced, knowledgeable members of
the forum.

I would like to isolate the problem of my son’s 1999 F-150 (2/w, f/disk, r/drum, 6cyc.), it
has sticking or dragging front disc brakes. The existing brake hose look like they have
been replaced but we do not know when.

So far we have installed a new drivers side caliper, and new pads for both front wheels,
and bled the system.
Vehicle history is unknown, he got it from where he worked about 6 months ago, it has
170K on it but it was a fleet truck and taken care of by a leasing company that provided
the trucks.

I”m just guessing but of all the reasons listed above, the booster adjustment rod might be
a good place to start. What bothers me about this is why would this adjustment change
with time?

If my thinking is correct in theory , if I even loosen the master cylinder from the booster
the wheels should turn freely suddenly. Of course, then further examination of clearance
of the rod and master cylinder spool would need to be determined. This might get a little
tricky. From the front of the truck and facing the firewall I think turning the adjuster to
the right would increase clearance, perhaps 1/2 turn at a time, then retry.

Am I in the ballpark on troubleshooting this?