Suspension Air Bags
Suspension Air Bags
Air bags are also called air springs. They are essentially big rubber balloons that fit inside the rear springs (or on top, for the leaf spring vehicles). They preload the suspension similar to air shocks, but are more controllable. You can load the right side harder to plant that tire down firmer, while leaving the left nearly unassisted, to provide fairly even traction left-to-right.
They sit right inside the rear coils and air up to assist the springs. (actually, they resist the springs, making them harder to compress). They act similarly to air shocks, but they leave those mounting points free to put useful shocks in their place. Let's face it, air shocks leave a lot to be desired for control and ride. The air bags can be inflated independently, and allow for preloading the right side of the axle. This effectively puts more weight on the drive tire, making it harder to break loose. Result: instant posi.
Plus, without the air shocks, you can have more axle control and less chance of wheel hop. This is an aspect that makes them desirable even with existing posi's. They install literally in minutes. The most time consuming part is running the air lines. Mount the air valve beind the license plate - some models already have a mounting hole (probably for an air shock valve). A couple of 5/16" holes does the trick. Or you can take out the rubber stops on the license plate pocket and stick the valves there. I've got an air guage clipped to the back of the license plate to make checking them a breeze.
The bags just squish up and you squeeze them in through the expanded coils of the springs. It takes a little effort when they are almost in. Just wiggle them around a little. You let them go when the last part of the bag has cleared the coil, and they pop back into shape, and then you simply plug them in to the air lines. Run the air lines through the frame. I'd recommend putting some 5/16" fuel line around the lines to protect them from rubbing. Some models come with heat shields - a good idea to use them to protect your investment. The whole thing can be done with a jack and a pair of pliers. The jack is probably optional. Well worth $60.
They work awesome. There are different versions available. The day I put them on, I took a friend out and tried for hours to prove that I had not changed the open rear to a posi! Gravel, pavement, water, didn't matter, I couldn't break loose! I finally had to unload one of the bags and do a bit of a smokeshow, and that finally convinced him. Very impressive items.
And if you already have an anti-spin or posi differential, definately get a set! I'd actually recommend them highly. In addition to controlling axle movement with the shocks, you can preload the suspension to give equal traction characteristics and control/prevent/reduce wheel hop (i.e. put more power to the ground).
Posi-traction is great, but the ability to load each wheel separately was invaluable. I don't see why it wouldn't be fine on a street car. The driving and ride are not compromised at all. Control of the rear is what you are getting here. Different air pressures and combinations give you different traction results.
[ Thanks to Charley Buehner, Bill Culp for this information ]