WOW, if its compressing that much its proly blown or your 400lbs Adjust the comp nob at the top of the shock ALL the way to the right and that will stiffen it up some. You can also tighten down the spring at the top also with an adjustable spanner wrench, or if your ghetto, a hammer and punch will get it done. Its easier to adjust that nut with no weight on the rear susp and it hanging free with the rear wheels off the ground. You can rebuild the rear shee shock for pretty cheep also. Give the adjustment a go. Then check back.