The pads should be about 1/4" thick.
There is pad on the transmisison side, then the disc, then another pad, a thin piece of sheet metal, and then 1/4" two pins inside the outer cover. A lever connects to the center of the outer cover. When you move the lever, it pushes on the pins and forces the pads together. The pins are known to rust in the aluminum cover. the cover is held on with two 3/8" bolts. Remove cover and loosen pins up. The center nut that holds the lever can be tightened to put more pressure on the pads.
To avoid breaking the 3/8" bolts, you might be able to remove the center nut and lever in order to free up the two pins.