GETTING SERIOUS AIR

We knew there'd be trouble from the start. On our recent desert expedition we used a 78 Series Cruiser cab chassis, with a steel tray and a Candy Canvas slide-on camper, as our 'chuck' wagon and also as a home for our Red Desert catering crew.

While the Cruiser wasn't particularly heavily loaded - just a camper, two spare tyres, food, water, a couple of fridges plus assorted tables and chairs, along with some personal gear - its rear end was really dragging. I guess manufacturers soften the spring rate to make them ride comfortably from the start and so the vehicle can't carry a load without a case of brewer's droop.

Such was the case with our Cruiser.

By the time we were in Alice Springs we had to sort out the suspension. Our TJM crew came to the rescue with knowledge that Polyair Bellows were just about to be released in Australia. After a few phone calls, an airfreight delivery to Alice and a trip to Pete at Elston's Auto Repairs, I got my first look at the new bellows system and our problem was nearly solved.

Designed for Ford F100 and 150s, along with Chevy utes and Suburbans, the Polyair Bellows System has been available in the USA for a few years. Now they are also available for LandCruiser 75, 78 and 79 Series and will soon be available for leaf-sprung versions of the Patrol cab chassis.

Made from a high-strength 2-ply glass-reinforced nylon, the airbags or bellows that carry the load are very similar to those under big trucks and interstate buses. This proven technology is widely accepted in the heavy-haulage industry but we haven't seen too many in four-wheel drives.

While you could install these yourself - and the kit does come with fitting instructions - most people will find it easier to get a professional to do it. It's a job that takes a few hours for a trained person with all the right gear and there is a bit of sweat and muscle involved.

4X4 ON THE RISE: INSTALLING POLYAIR BELLOWS
Height before - 270mm	Height after - 420mm	Installing the airbags - upper bracket
The upper bracket up close	Note the heat reflector between exhaust and airbag	Running the airlines	The airline is kept on top ofthe chassis rail to avoid ripping

The kit includes air bellows, mounting brackets, airlines, inflation valves, and mounting hardware. The system is installed by first removing the rear bump-stop rubbers and then mounting the bellows between the chassis rail and the axle, using the spring's U-bolts to locate the lower bracket on the axle. The inflation valve is placed in a convenient spot. It's important that the air hoses are routed correctly from this point to the bellows so there is no danger of rips or damage.

As with any Polyair airbags there's a minimum and maximum pressure. Minimum is just 5psi (35 kPa); maximum is a hefty load-carrying 100psi (690 kPa), far greater than standard Polyair spring airbags.

For varying loads, Polyair suggests a bellows pressure of 25 to 35 psi for a 1000-lbs (500 kg) load up to 90 to 100 psi for a 4000-lb (2000kg) load. We put 55 psi (380 kPa) into the bags and the result was fantastic. The tow bar, which had been dragging along just 270mm (10.5 inches) off the ground, now had a clearance of 420mm (16.4 inches). Our headlights were now shining along the road rather than spotting possums, and the Cruiser's handling and ride had greatly improved.

The bellows were sturdy and we had no concerns with the airlines, even though there were plenty of bag-tearing, hose-ripping sticks and bushes on our cross-country travels.

The bellows system costs $695 plus fitting but, presently, it's only available for a limited range of vehicles.

A recent Polyair innovation is a cab-mounted pressure monitoring and control system consisting of a switch, twin gauges and a low-pressure switch. This means that, with an air compressor under the bonnet, you can easily control the pressure in the bellows. Price is $480 which includes an air compressor.

Over recent months, I've tested quite a few suspension aids and, while more expensive than many, the Polyair Bellows offer the greatest flexibility for varying loads and have also proven tough enough for the heaviest-duty job.

This article reproduced courtesy of 4x4 Australia

Footnote: The prices quoted in this magazine article were correct at time of printing (2001). Check with 4WD World on 1800 807 176 for the current pricing and also which makes and models of vehicles Polyair "air bellows" are available for.
Note: Air bellows are for leaf sprung vehicles. Polyairs are for coil sprung vehicles.

More Info: POLYAIR BELLOWS AIR ASSIST SPRINGS