How and what do you need to replace rear break pads on a 94 mercury sable 3.0

Replace caliper with old brake pads put 1 bolt in place to hold together while taking a large screwdriver and prying caliper piston so that it compresses piston & block wedge to rear of bracket it should make enough room to install on new brake pads, the other way is to use a large c clamp put 1/4 pice of wood in between c clamp and caliper so you don't damage or Mar the caliper also check YouTube.

the caliper is probably bad.

Hello, Most likely you have broken Emergency brake pads trapped inside the inner rear Rotor or drum. There is also a possibility that a rear wheel bearing has collapsed especially if you have heard a whining noise while driving.

Since the Sable is a Front-wheel drive vehicle, the rear wheels have few parts. This will not cost as much to fix. The rear rotor/drum will need to be removed and the defective parts replaced. The rear rotor/drum will probably be bad along with needing pads or bearings.

The other rear wheel should be checked for damage too. I hope my solution is helpful to you.

Your car probably has a transmission cooler located parallel or near the engine coolant radiator. These flimsy things eventually fail but if you are lucky, it may be a connecting line only. You'll have to locate the lines and cooler from below.
This needs to be done soon, otherwise you will lose enough to break down once the transmission starts slipping from low pressure and fluid level.

open the trunk and remove the inner liner behind the break light lenses and remove the 6 bolts that hold the lense in place

The type that compress have a large"X" or a slot on the caliper piston. This is to allow a tool to "turn" it.
The push in style are cupped or flat.

Look for a loose connection in the rear wiring harness which may be accessed by removing the panel in the left rear of the car (inside)

low brake fluid.
Also by your e-brake, there is a switch there you can disconnect.

REACH WAY BACK, MOST LIKELY YOU WILL BREAK THE WIRES WHEN REMOVING THEM FROM THE SPARK PLUGS

I have done brakes jobs problem is Kia Sportage last one hammer out the pads, service breaks every year.This is the problem before or after winter service breaks.