I think you've got it too tight, 1/4" is almost no deflection. I would say at least 1/2" or more. As long as it doesn't slip it's tight enough.

But, a picture would help ....

 

I'll give her a shot!

 

Tightening it less will not help you if you don't have the brackets set up correctly. The alternator should not come out of alignment at all no matter how tight you adjust it. These are the brackets you should be using for an early V8 car. http://www.cjponyparts.com/ALTERNATO...4-1969/p/ALTB/ If you don't have these then you need to get them before you go any farther.

 

I believe its a 6. I can't remember how the alternator is mounted on a 6, that's why I asked for pictures. But you are correct, at least one of the mounting points should only allow it to pivot with no slop.

 

it's a 6 cyl. it looks exactly like the photo in NPD catalog. here's a photo.

 

OK, show us the bracket bolted to the engine.

 

here ya go...........

 

The other bracket, the one on the bottom.

 

2+2GT.... my bracket looks exactly like your photo.

 

The top bracket you are showing will not keep the alternator in line, the one 2+2 showed is the one that keeps it steady. I'm betting that it has worked it's way loose. Either that or the large bolt that the alternator pivots on is not tight enough. For adjustment, you loosen the big bolt just enough to let the alt. pivot, adjust your belt tension with the top arm and bolt, then tighten back up the pivot bolt. But if the mount for the pivot bolt is loose, that would be your problem.