I just paid $500.00 to replace all brake pads and the front rotors
The Mercury Mountaineer has hydraulic brakes, not air brakes.
The brakes on the Villager are as straight forward as the brakes on a 1965 Mercury. Only normal brake tools are required.
Pads on front, drums or pads at rear. Ask at a good auto part store with year of car
It sounds like you need to bleed the system of air.
Any Auto Parts store can provide you with this information.
replace calipers in pairs. replace brake hoses at the same time.
did you replace the master cylinder if so it has to be bleed frist
The best way is to go to a junk yard and pull the disk brake assembly off of a Cougar, or a Contour/Mystique, the latter two will require you still purchase a Cougar specific E-Brake cable though. There's plenty of info on this conversion in the wheels, tires, and brakes section at the newcougar.org forums.
Brakes come in two types: disc or drum.See "Related Questions" below for coverage of both types...
It would be to your advantage to take your car to a Brake Repair Shop if you have to ask that question brakes are not something you should do if you do not have the skill, WBMS
This is as complex procedure. I suggest you buy a repair manual if it is not obvious to you, and you don't have experience.
A 1991 mercury topaz has drum brakes on the rear wheels.