1974 Porsche 914 2.0. My parking brake doesn't fully engage. When I'm on a hill, the car slides (with some drag). Today, I put the car up on stands and removed the rear wheels. First thing I noticed was that the rear left wheel has A LOT of drag without parking brake engaged. The rear right is better. I set the venting clearances on both the outside adjusters to .004, but the inside adjuster caps are stripped, so I'm going to have to pull off the calipers and figure that out.

Question though, how do I know if the calipers are seized? Or could it be the lines? Or simply the inner adjuster clearances?

You need to set the proper venting clearance.
I found a little controversy on this subject so hopefully everyone will chime in on this and you will get the correct info.

Take the calipers off and send them here. http://www.pmbperformance.com/catalog.html

Yes, I'm thinking of sending them to Eric. However, how do I know if they are seized completely? Is there a way I can test? Details please! (I'm not great at fixing cars, yet.)

I wish Gunn1 was here to advise.

I'm thinking of removing one of the rear calipers so that I can whack at the adjuster cover and hopefully dislodge it. If I disconnect the brake line, can I simply plug it so that the brake fluid doesn't spill out? Or, do I have to completely empty the lines before I remove the caliper?

It might be a good time to flush out and replace all the brake fluid anyway. Not hard to do. Bleeding the brakes can take a little time but there are some easy techniques to do that.

Good point Elliot. I'll try to plug first, and if that doesn't work, then I'll just flush and bleed!