Speaking in pure general terms, there would appear to be something else wrong. If the is an adjustable pinion snubber it must have been added as an aftermarket unit. Even with the rubber in place, it really shouldn't be making hard contact unless its under extreme launches at the drag strip. You didn't state under what circumstances this situation arises. Now with the snubber missing and extra clearence it should be happening less. Sounds more like severe spring wrap. I'd be taking a closer look at springs and what they're attached to. Might be the syptom and not the cause.