Town Car Air Suspension Systems- How It Works

Now where can i start with car air suspension or pro bag air suspension as known in Australia, being as i work on cars myself and there's has been a few times where i have experienced problems with air bag suspension or air shocks, from jacking in the wrong places and braking the motor mechanism to jacking up with out correct procedure and causing a loud hissing noise because the bag has just split.

If you own or thinking about owning a vehicle with air suspension read on further or click on the links to learn more about it.

For most people air suspension are not known about unless you own or have owned an SUV or 4x4 or if you work in the motor trade,although it seems like it to me. It just so happens that several cars were offered air suspension in the 1950's.

Unfortunately, as I'm sure you can imagine materials and technology in those days still had a long way to go and the rubber bags used instead of coil springs were not great and didn't seem to last. After majority of people found their vehicles sitting flat on the ground, most owners got rather fed up on that matter plus the spend out, they soon chose to replace the air suspension systems with steel coil springs.

Today, materials and technology are much more advanced and still progressing every day. Air suspension is used on mostly large trucks and buses hence when you hear them drive past or pull up you hear a loud hiss like an inflated tyre going bang that's why some buses when they stop they lower so you can get on them (that's what happens on a normal 4x4).

Its durability is measured in 100,000's miles, several modern road vehicles are using air suspension too like range rover, BMW x5 and some Mercedes 4x4 too. Range rover calls their system 'cross-link electronic air suspension' and they say it offers the best on and off road ride comfort and handling.

The cross-link four-wheel suspension is the third generation of air suspension used today, mainly on range rovers. McPherson struts are used in the front with rubber air bags mounted on the top of the struts (these strut set ups are the same as ford escorts and fiestas).

Rear suspension uses control arms (also known as track control arms) to position the wheels and separate shock absorbers from the air bags to support the vehicle. You normally adjust the camber of the wheel with these by moving the bolt that goes through the control arm.

One big benifit of air bags instead of coil springs is reduced un-sprung weight. The weight is defined as the mass that is not supported by the vehicles springs. This includes other vehicle parts like the wheels ,tyres, hubs, brakes and on most suspensions, part of the axle, control arms and shock absorbers.

Reducing weight allows the tyres to react faster to road humps and bumps and gain more traction without effecting the vehicles handling and ride. The benefit of air suspension on the range rover is the ability to change the vehicles ride height to suit the road condition.

Four different heights are programmed into the air suspension control. Three of these are selectable with a console-mounted switch, For on-road driving, the suspension is set to standard height.

The computer uses height sensors at each wheel to adjust the air pressure inside each air bag to keep the vehicle level. If vehicle speed travels faster than 70mph (100km/h), the computer automatically lowers the vehicle 20mm for improved high speed handling (being lower to the ground at speed is better gravitational force).

Getting a full size SUV can be quite a hike for some passengers so the range rover suspension can be lowered at the push of a button by 40mm. Appropriately, this is called access ride-height and it only selectable at speeds below 15mph (24km/h). If the vehicle speed increases, the computer raises the suspension back up to standard height.

Off-road driving is aided by increased ground clearance. The range rover air suspension can raise the front of a vehicle 60mm and rear 50 mm above standard height, selecting off-road ride height also activates the cross-link suspension control.

THE CROSS-LINK SUSPENSION

The cross-link suspension links both front airbags together and both rear airbags together. One control valve is used at each end of the vehicle to control airflow through the airlines linking the airbags. When a valve is opened, the springs exchange air, making it easier for the wheels to move up and down to follow the terrain. When one wheel is forced up by the ground, the other wheel is forced down by the air transferred to that wheels airbag, improving the traction on the unloaded wheel.

The cross-link suspension concept is very simple. Two air bags are connected by an air line, computer control of the suspension allows the cross-link operation at low speeds while enable ride height changes at other speeds.

The cross-link air suspension reduces the side to side motion so even the roughest off road course feels more like a ride down a country lane. The added benefit of transferring weight to the unloaded wheels help traction so the range rover can plough difficult terrain that stops many other vehicles.

The true test of any suspension is in the driving seat and you know what.......the range rover passes eveyrtime.

On the road the ride is smooth, bumps and rough roads are hardly noticeable. Off-road performance is astounding and fun, feels like a simulater ride. Other SUV and 4x4s beat occupants up as they bounce from side to side on rough uneven terrain.

Air suspension isn't perfect. The weakest link is still the air lines that connect each air bag to the compressor and air reservoir. Break an air line and the vehicle will look like a low rider.

Fortunately, the range rovers air lines are well protected, helping it to have one of the best on and off-road suspension combinations on the market.

CHANGING A WHEEL

Now its not easy changing a wheel on a range rover or BMW x5, the amount of people that tell me they had to pay £500 plus to replace the air bag on the suspension due to not jacking up in the right places, now all 4x4 may differ but if you do this for every one I'm sure you cant go wrong.

OK with most Land Rovers, Range Rovers, BMW etc.. all you do it put on the hazard lights on and open the rear tailgate (trunk,boot), some of these may have a jacking mode in which you will have to set the computer to the correct mode, by doing this it tells the on board computer there is a problem and will stop the suspension from working.

When jacking up the vehicle make sure you only raise it on the under body or heavy duty points if visible, what ever you do do not jack it up on the near side or passenger side (UK cars only) seal all other cars that are left hand drive, will be driver side or offside (outside UK).

The reason for this is that the motor that controls the suspension is there and like i found out when i did my first ever i crushed it and the car made a loud whining noise and did not raise or lower after that. After refitting the wheel let the jack down slowly, the reason for doing this slowly is because there may still be air in the bag and fast impact pressure could pop them.

So now that the wheel is firmly on the ground tighten and recheck the wheel nuts, then start the engine and wait for about a minute, raise the car up to its full height, once complete lower to lowest ride and then back to normal ride height (just make sure all doors are closed otherwise the vehicle wont rise or lower).

Well i hope this helps you, check out the pictures below for jacking points suggestions.