The Jounce Shock provides the core of a secondary suspension system. They aren't cheap but they do work. This review deals with how they work, some problems encountered by forum members who run jounce shocks and how Light Racing is dealing with the problem.
Most systems are designed such that the JounceShocks do not engage the suspension of your vehicle at ride height. Therefore the system does not usually alter the ride height or on-road ride quality of your vehicle. When you have a heavy payload or take your vehicle off-road, your suspension will compress more and engage the JounceShocks. When the suspension engages the JounceShocks, you may hear the initial contact. This is normal and is an indication that the JounceShocks are being applied. As the vehicle is driven off-road you will notice a couple of performance gains. First, as you drive the vehicle over rough terrain you will notice that it never feels as though the vehicle is bottoming. These changes significantly enhance the ability of the vehicle, the durability of the vehicle, and the comfort level of the occupants. This added capacity can be misleading (ask JESHUA) because it allows you to push the rig harder without "feeling it".
How a JounceShock works-
When the suspension compresses it drives the shaft of the JounceShock into the JounceShock body. The shaft compresses the nitrogen volume and since the nitrogen is in a closed cylinder, the nitrogen pressure increases dramatically as it compresses. This gives a smooth exponential increase in force (like an air spring) instead of the force spike that occurs when typical suspension systems bottom out onto the hard rubber bump stops on the FJ. The valving inside the JounceShock is designed such that after the JounceShock has compressed the suspension falls away faster than the JounceShock can extend. Therefore all of the energy that was put into compressing the JounceShock is dissipated by the valving rather than pushing the suspension back out. This is a key factor in why the JounceShocks are so effective for high energy absorption and vehicle control.
Recently JESHUA and I both lost front jounce shocks on the trail. This week I had one of the rears come loose on me. This is a failing that Light Racing is aware of because it replaced Joshua's and my "missing" shocks free of charge -- customer service to be noted if you plan to make a purchase -- they do stand behind their product.
DEMELLO OFFROAD is working on a solution to keep the jounce shocks in place. Keep in mind that mine came loose after six months of hard driving.
Like Larry said they will mislead you so you push the rig much harder if that is your cup of tea. But I pushed my hard even before the chubby's so I am screwed ether way. If you do install make sure you get the new cup mounts up front that have a set screw so they wont fall out. As for the rear I am not sure if they have a mount back there that has a set screw I just used lots of loc-tight on mine when I installed them.
If I was going to do it over again I think I would go with some King air bumps like TCao did. It will end up being around the same cost sine they need a custom install but the bumps them self are cheaper then the Light Racing Jounce shocks.
Larry did the jounce get out of the rear coil or did the coil kind of keep it?
We have already come up with a solution to keep the front jounce shocks in place. We had issues with the Donahoe -labeled Light Racing built units a while back. We noticed that the bolt that holds the front shock cup in place threaded upward, and relied on Loctite to remain in place. If it came loose, you'd loose the entire jounce shock assembly (as some have already). We removed the bolt, and installed longer bolts that would thread up through the welded nut far enough to install a lock nut on the top side. This way, the bolt could not back out and come loose. We have yet to lose another jounce stop since implementing the change. We notified Light Racing about the problem, and they started to include the longer bolts with nuts in their kits. We noticed recent kits have fallen back to the old style shorter bolts again - so it's time to help them save a whole lot of money and customer frustration by calling them back again and reminding them about the problem, and the cure...