While instructing my younger son, who'll soon be licensed, to change the rear pads on the 93 940 wagon this past Sunday, I found the passenger side caliper had a piston stuck. I have him install it anyway so the car can be back on the road. The new pads won't go in by the way because of the stuck piston. I have him put in a used pad I happen to save in a box. I presume a rebuild kit won't do because the caliper probably needs to be replaced. So getting a rebuild caliper is the way to go. Now the question. Is there a way to tell which caliper the car has? The mail order outfit says there are three different types of calipers for my car, 36mm piston, 38mm and 40mm. I really hate to take the wheel off to check again.