This page contains contributions list members have made regarding modifications to their suspensions. The very first thing to keep in mind is that suspensions are much more complex than they seem. The arangement of, what amounts to simple bars of steel and pieces of rubber, adds up to complex dynamic force distributiona and management system that requires a great deal of testing and expertise to set up in a safe manner. Something that seems logical and simple can have dire safety implications if not properly executed. One of the simplest and most frequently made suspension modifications to the D-90 (and many other vehicles whose owners want better off-road performance) is removal of the sway (or anti-roll) bars to increase articulation. If you do this, not only will you notice a difference in how the vehicle handles (increased sway and body lean on curves), and have to adjust your driving accordingly, but you may have let yourself in for trouble or even litigation if you are involved in an on-road accident, as you have modified a significant safety feature of the vehicle (in the eyes of the National Transportation Safety Board). Any other suspension modifications could fall under similar scruitiny. The best course of action when one considers suspension modifications is to talk to others who have done the same or similar things. Take a ride in their truck if possible to get a real feel for the mod. ALWAYS deal with reputable companies who have tested and sold their proposed modifications. And most of all, drive very conservatively after any suspension change until you get used to the new handling characteristics of the vehicle. Don't be afraid to ubgrade your truck to meet your needs, hundreds of others have successfully done so before you. Just be sure you fully understand those needs and don't go too far in one direction at the expense of other attributes.
Find some good general info at: http://www.geocities.com/MotorCity/2195/suspension_bible.html