figuring out how much slip in a drive shaft?

Is there a way other than exercising the suspension to figure out how much compression I need on my rear drive shaft?

I am a little concerned about the ds I put in over the weekend, as it only has 1/2"-3/4" of "squish". I loaded 360lbs of cement in the back and had a 200lb buddy jump on the bumper and it didn't compress all the way, so im thinking it might be ok, but I wanted to check with the experts.

Thanks

3/4" of travel should be enough.

You can disconnect it at the axle, push it in as far as it will go and mark it. Re connect and measure. ?? X2 ^^ shouldn't need much.