AirLift® Rear Air Suspension

The weight of the new Bulletproof^® bumper made JeepThing's rear end sag badly, compromising its departure angle. On the last trip to Tellico the gas tank skid plate really took a beating on every rock. Upgrading to 4" Teraflex^® springs helped, but the rear still sagged 3/4" and dropped almost 1 1/2" with the addition of my wife and kids, cooler, a toolbox and spare parts. I needed a solution that would retain the original ride quality when unloaded but can also be adjusted to accommodate heavy loads. The August 1998 issue of 4Wheeler Magazine showed the installation of an AirLift^® rear suspension system onto their project Back in Black TJ, gaining the ability to raise and lower the vehicle height at will.

AirLift specializes in aftermarket air suspension components for different automotive applications, from ground-slamming low riders to autoleveling systems for RV's and leaf-sprung pickups. They recently began to offer an Outback package for SUV owners primarily for towing and load carrying use. The Outback package includes all necessary hardware - two airbags, compressor, and the necessary valves, hoses and gauges. The kit includes a safety valve that maintains a minimum 5 psi. of pressure in order to prevent chafing of the bag against the coils. You have a choice of kits that inflate both bags through a T-fitting and a single air line, or individually controlling each bag with dual controllers. Airlift does offer an Outback package for stock TJs, but not for lifted vehicles. Tech support at AirLift was quite helpful, and provided me with the proper airbag part number after I measured the distance from the lower spring pad to the base of the bumpstop (8" in my case).  I ordered the Outback II kit that allows individual bag control from a local RV shop (AirLift does not sell directly to consumers) - the total cost was $99 for the bags and $200 for the dual compressor setup.

In the 4Wheeler write-up the bumpstop never touched the deflated airbag - riding instead in a small depression in the center of the bag. JeepThing already sat low in the rear when empty, so I needed a little boost from the partially deflated bag. To accomplish this I reinstalled the 1" bumpstop spacer originally installed with the Teraflex 3" kit - lowering the height of the bumpstop and restoring JeepThing to a level state.

INSTALLATION

First, raise the Jeep with jackstands placed under the frame. It is important to raise the vehicle high enough to allow the suspension to droop without touching the floor. Remove the rear wheels and disconnect the shocks at their lower mounts. Use a floorjack to raise the axle to its normal level, then disconnect the swaybar links from the axle by removing the lower connecting bolts. Then disconnect the track bar from the frame by removing the upper mounting bolt. Remove the jack and allow the axle to hang - just be sure that the rear brake lines are not stretched excessively.

The coil spring can be removed by using your foot to push down on the brake drum, pushing the axle down and allowing the spring to be worked free by rotating and pulling outwards at the base of the spring. It may be helpful to have a spring compressor handy just in case you have problems (I bought a cheapo model for $20 at the local Western Auto Supply).

The lower spring pad needs to be drilled to to allow the air line to pass into the airbag. AirLift's instructions call for a 3/8" hole, but I followed 4Wheeler's suggestion and drilled a 1/2" hole in the center of the pad before installing a rubber grommet to prevent excessive chafing. Be sure to place the hole in the center of the spring pad to prevent possible binding.

Note the 1 x 4" piece that was removed from the rear of the pad. Lifted TJ's equipped with the optional Dana 44 rear axle tend to pinch the shock absorber canister against the back of the lower spring pad at full droop. Unfortunately Rancho does not recommend mounting their 9000 series shocks upside down, so short of repositioning the shock mounts this is the best possible solution.

Saw the rubber bumpstop flush with the level of its retaining cup. This is the contact surface against the top of the bag, so make it as smooth as possible. If you are working with an upgraded Teraflex 4" kit (like I did) and need to raise the empty height, you will need to first remove the bumpstop bumper and cup and reinstall the 1" aluminum spacer that originally came with the Teraflex 3" kit (you can see the bottom edge of it in the right-hand picture below. If you don't install a spacer then the bag will be unloaded at rest and will come into play only with inflation or added weight.

Heat shields have to be installed on the tailpipe to prevent the passenger side airbag and hose from melting. The kit supplies two malleable shields that are held onto the tailpipe with hose clamps. The tabs on each end of the shield are bent into two right angles, and these tabs are clamped against the tailpipe.

Install the airbags into the coil springs, making sure that the nippled end is on the bottom. The bags are quite stiff and it is difficult to fit them through the coils or the ends. It helps to squeeze the air out of them and cap the nipple with the supplied plug. Trying to zip-tie the bags into a rolled bundle (as illustrated in 4Wheeler) was impossible. Try to get the bag as close to the bottom of the spring as possible before removing the nipple and re-expanding the bag. Next, feed one end of the flexible airhose through the spring pad hole and connect it to the nipple using the supplied clamp. I routed the other end of the airline through the lower shock bracket, then next to the brake lines as they cross over the top of the axle and differential housing.

The supplied plastic pad is then slipped between the bottom end of the pad and the endloop of the spring. The hose is fed through a hole in the center of the pad.

The spring assembly is reinstalled onto the axle. Feed the top of the spring around the bumpstop, then gently maneuver the bottom into position without pinching the hose. Reconnect the trackbar, sway bar, and shocks in that order. Use a floorjack under the differential housing to raise the axle enough to allow the free end of the trackbar to fit into its bracket.  Below are shots of the suspension at maximum droop (with everything disconnected) and at normal load.

As you can see there is a lot of potential droop in the TJ's rear suspension. The shocks do limit downtravel, but unless the mounting points are relocated, switching to a longer shock would limit the amount of compression. Currently there are Rancho RS9116's mounted in the rear with JKS bar pin eliminators adding 1" to the height. This was a perfect setup before the AirLift. I remove the lynch pins from the TKSlider^® rear sway bar links before I 'wheel to prevent any loss of articulation that the rear swaybar may cause. Extended length braided stainless steel brake lines from Explorer ProComp were added to prevent damage at full droop. The stock track bar also limits droop because the ends bind within their brackets. Unfortunately there is no available bolt-on replacement solution to this yet.

I chose to run the airlines to the compressor along the driverside framerail to minimize the risk of heat damage from the exhaust system. The line from the passenger side bag follows the rear brake line over the top of the axle to the driver's side. The airlines from each bag then run towards the driverside rear fenderwell, where two holes were drilled in the body flange and the external bleed valves for each bag were mounted. This body flange was accessible for use due to the 1" body lift installed on JeepThing. These valves can be used to air up the bags in case of compressor failure, or to bleed the system if the solenoid valves fail.

AirLift's instructions state that the compressor can be mounted anywhere under the vehicle against the framerails. I chose to mount the compressor in the engine compartment to minimize water and dirt contamination. Unfortunately space within a 6 cylinder-equipped TJ is scarce. The stock airbox and filter element was removed and the steel accessory platform from Turbo City was installed using the original airbox mounting holes. The compressor was mounted onto this. I chose to install Turbo City's Rockit intake plenum tube and a PowerStack open air filter in place of the stock units. The PowerStack is similar to the K&N product, but is also open at the end. This was purchased from Rubicon Express.

A single semirigid airhose connects the compressor through a T fitting to each solenoid, which in turn is routed to each bag's airline near the bleed valves.  There is a lot of hoses and wiring that I wrapped in flexible plastic loom material (found at any Radio Shack) to protect it and make it more aesthetically appealing.

The kit includes a mounting bracket for the power switch and the pressure dials and air release valves for each bag. I decided to mount the controls on my rollcage, and fabricated a custom enclosure for it.

It took me a Saturday night and a Sunday afternoon to do all this by myself in the garage. The instructions from AirLift are slightly confusing so installing the first airbag took all Saturday night, but the other side took only 2 hours on Sunday. Most of the time was spent finding the best way to route the hoses and wires.

RESULTS

JeepThing now sits level regardless of load. With the bags at the minimum 5 psi the ride is unchanged from before. With the bags pumped to the maximum recommended pressure of 35 psi the rear end gains up to 2" of additional height within 30 seconds. Deflating the bags takes 15 seconds.

Theoretically the simpler kit that connects both bags together with a T fitting would also give some individual airbag action. As one wheel is pushed up into the wheelwell the pressure between the bags should equalize - pushing the opposite wheel harder into the ground. I cannot vouch as to whether this truly works in a trail situation, nor do I know how fast this would happen given the small caliber of the airhoses. I went with the dual setup because I know it will work, and because of the ever-important "Drool Factor"!

The addition of the airbags does not significantly affect the RTI due to the compressability of the bags and the lack of a bumpstop. The bag still bulges slightly between each coil, preventing the coils from touching one another. However in the original configuration the coils were similarly limited due to the length of the original bumpstop.

Drooped Side                                          Compressed Side

How does it do on the ramp? The bag on the droop side of the axle was inflated to 35 psi, and the compressed bag was deflated to 5 psi. Here's some pictures of JeepThing maxing out the 20 degree ramp at the Jacksonville 4 Wheel Parts Wholesalers- the opposite tire was hitting the curb preventing further progress. That's  a score of 1140, folks.

I'm happy and completely satisfied with the kit. Now off to the rocks!