I'm in the process of replacing rear brake shoes and cylinders on a 1966 122s. I've got the drum off one, working on another. This is my first brake job on a car. No doubt I'm making mistakes as I go. Here are my questions. The first one reveals my ignorance of basic knowledge about drive-train engineering on cars:

1. If the car is in gear (& obviously up on jacks) should the rear axle turn? In working to get the drum off, I found that the axle was spinning. (I used a pry bar to stop the motion when banging on the drum puller.) What's the engineering principle in play that allows the axle to move when the car's in the air but in gear? (I thought the engine compression/being in gear would create resistance, like on a BMW motorcycle). Also, should the car be in gear when banging away on the drum puller? Could I damage the drive train in banging on the drum puller if the car is in gear? Maybe already have?

2. Does somebody know the diameter of the nut on the brake line fitting where it attaches to the rear brake cylinder. I want to get a flare wrench that fits. Thanks in advance.