[Jeroen]

When it comes to air suspension there is a pretty strict divide amongst petrol heads. Some believe it is the best thing since sliced bread was invented. And some believe it is a hugely complex, and maintenance-prone, gadget at best.

However, those who have experience with air suspension will agree on one thing: It provides a superb ride! Mind you, not on all cars with air suspension. But for instance, the Range Rover air suspension gives a ride that simply is beyond your wildest imagination. There is a reason film and TV crews use Range Rovers as tracking vehicles. It is not necessary about the reliability of the vehicle as such, but the ride quality necessary for filming these fantastic driving shots. (E.g. TopGear, Grand Tour and so on)

Although I don't have actual data, I suspect most of the air suspension systems to be pretty reliable. For no other reason, they are found on expensive high-end cars, that usually get this sort of stuff right. So I am not sure how much of the moaning on the internet when it comes to air suspension is from people who have owned air suspension-equipped cars for a long time. Just my thought.

I do know one guy, my best friend Peter who certainly raked up considerable air suspension miles; Peter is onto his third Jaguar 350. In over 800000 km (yes, that is eight hundred thousand!) he has experienced only one failure. It occurred on his first X350 after hitting 450000 (yes, four hundred and fifty thousand kilometres). It is just one data point, but even so.

I attended a technical workshop at my favourite Jaguar XJ specialist G&G Autoservices here in the Netherlands. I have written about them numerous times in my "fiddling" thread. The owners are Raymond and Joke. Raymond is one, if not the most accomplished, car guy I have ever met. He chose to specialise in not only one brand (Jaguar) but also in one type, the later Modern XJ series, so
the X300, X308 and X350.

Scroll through this post to get a feel for Raymond and G&G. This is about an earlier technical day, where amongst other things Raymond pulled a complete automatic transmission apart!!

https://www.team-bhp.com/forum/diy-d...ml#post4180547 (My Car Hobby: Jaguar XJR, Mercedes W123, Alfa Romeo Spider, Jeep Cherokee & Mini One)

For this technical day, Raymond and his mechanic Petra had spent quite some time preparing to show us everything there is to know about air suspensions and how to troubleshoot them.


Raymond started with a prepared X350 on the lift. If you have a wheel alignment done by an outfit that doesn't know the ins and outs of each system you might find yourself in trouble afterwards.



The steering wheel needs to be positioned, dead centre! Not half a degree off or so. There are only two ways to accomplish this, with a special level or on some cars, (e.g. Mercedes) the steering house provides a mechanical dead centre lock.



If you ever get any car aligned and they just position the steering wheel horizontally by feel/view leave immediately! On modern cars with electromechanical steering, the dead-centre position is more important than ever!!

If the connection between the steering wheel and the steering box has been worked, or the steering box has been removed for overhaul, on most cars you need to follow a very different procedure to align the steering box with the steering wheel first. (Those who follow my "fiddling" thread will have read about my experiences with the wheel alignment on my W123 after I had the steering box overhauled. None of the alignment workshops here in the Netherlands wanted to help me, as I demanded we check the steering box to steering wheel alignment first with a special dead-centre tool. Finally found a guy who knew what he was doing and was very happy to accommodate my request.

Raymond has put together this special valve manifold. With the various valves, he can operate all the different parts of the car suspension individually. Pretty nifty.





On many car suspension systems, you need to have a special OBD reader to control the suspension during wheel alignment. The Jaguar system has some 15 different modes of operation. From normal cruises, parking par, high-speed driving and so on. As you will see, understanding how this air suspension works is crucial to be able to fix it obviously, but also to perform a wheel alignment.

By the way, the Jaguar system is very similar to the Landrover system as you would expect. Even though the components look identical they can not be interchanged. Each component has a unique electronic code, that will allow proper operations only on a Jaguar or Landrover.


Raymond and Petra had built a small demonstration rig. Raymond added all the different components of the system during his talk. Just so we all got a good idea of what the components look like, what they do and how they interact with all the other components.

As you can see the basis of the system is four bellow in each of the wheel struts.



The system operates on a nominal pressure between 7 and 9 bar inside the bellows Just above 7 bar the car is being lifted. However, the air reservoir is kept at 15 bars.

Here you see it. It has a manifold with several electrical controlled valves.



Here you see it, in the boot of the X350 under the spare tire.



At the front, the bellows are quite a bit larger than at the rear. The front is heavier with the engine, but also it needs to accommodate larger forces when braking.

Next comes the compressor. Sits underneath the left-hand fender sort of.



These are quite capable compressors. They compress air up to 15 bars and must do so in a short space of time. As they are air-cooled, the compressor won't run until the speed is at 45 km/h. Even so, they are protected against overheating, so they will be switched off automatically after 2m minutes. A new original Jaguar compressor will fill the system in probably half to one minute. So it will switch off on the pressure. Non-original compressors often can't get the system up to the required pressure in under 2 minutes. So they get switched off by the timer before adequate pressure has been reached.

Here you see two compressors. The one on the left is the original one, the one on the left is a non-Jaguar brand. The price difference is staggering, literally several thousands of euros. An original Jaguar compressor costs about Euro 3000 (INR 270000)



Here is the original Jaguar compressor. One of the main differences is the Jaguar compressor comes equipped with a special patented valve. As with other air suspension components, without this special valve, the system will not work properly, or work at all.



The compressor does come with an air inlet filter and moisture absorptions. The latter needs regular attention as it can become saturated. One thing is how the various OBD error messages show up. The error message so-called "reservoir not plausible" could be due to problems with the compressor.

Next Raymond showed us the level sensors. Essentially a lever that rotates a potentiometer. The suspension computer calculates based on the level sensor, and a bunch of other parameters how much air should be directed to each of the four bellows.

Interestingly, the X350 has only one of these sensors at the front and two at the rear! The whole system is set up and calibrated by having the driver behind the wheel. So there are different computers for right-hand and left-hand drive Jaguars. And no, they are not interchangeable.



One of the reasons for having g two-level sensor is that the air suspension system also works in tandem with the ESP system. There are also other aspect of the car that are relevant to the air suspension. For instance, the steering angle sensor is an input to the suspension computer.

There are also two acceleration sensors fitted at the front of the car. One for horizontal and one for vertical acceleration.

Sorry, poor image, but you can just make them out I hope



All these sensors are hooked up to a special computer. Here you see Raymond holding one of those



Each suspension strut is equipped with a special air check valve that ensures a pressure of at least 3 bars is maintained at all times. These struts are shipped from the factory with 3 bars of pressure. So one of the checks Raymond does is check the pressure when receiving new struts.

Here you see the little valve, Rayond demonstrated with his nifty pneumatic control board the operation of these little, but important valve.



I trust by now you are beginning to get a feel for the complexity of this air suspension system. And why even a relatively simple wheel alignment needs to be done by somebody who understands this system.

Just to summarise a couple of the must-knows: The compressor will not run at speeds below 45 km/h. (a bit tricky with your Jag on the lift). When the engine gets switched off, depending on various parameters the car will start to drop height after about 120 seconds. The calibration of the system, and thus the wheel alignment, is based on somebody sitting behind the wheel. And the list goes on. So unless you know what you are doing, or have the correct equipment to simulate the correct position of the car on all four bellows before alignment it is going to go badly wrong.

Raymond showed us the various alignment readings in different positions. I was quite amazed to see how big an error you get!

The system is designed in such a way that each strut, or rather bellow, can only lift a quarter of the total weight of the car. Well, a little more.

Now let's have a look at the actual struts. They are comprised of a spring, a damper and the bellow.

Here you see the complete strut in a special Tool Raymond has recently purchased. Complete struts cost around Euro 2600 -3000. Raymond is going to over a special service to his customers to replace only the bellows and or the struts. Replacing the bellows is not offered by anyone yet. Most garages and workshops will just swap the original Jaguar strut for an aftermarket one. And that often leads to problems and disappointment.



this special tool allows Raymond and Petra to dismantle a strut safely. These springs are immensely strong. When working on suspension and springs you need to know what you are doing. You have to use special tools. I have seen people use improvised spring compressors, made from a couple of threaded studs bought at the local DIY centre. Extremely stupid and dangerous. The forces due to the spring are immense!



These are the actual bellows.





With the bellows removed







The damper is, similar to my Jaguar (XJR/X308) a so-called active damper. Jaguar calls it CATS (computer-operated active suspension control) ). On an active damper, the charasterstics of the damper can be adjusted. E.g. for different kinds of roads and terrain. These are all Bilstein. They cost a huge amount of money. The ones for the Jaguars work on a very simple principle, the fluid also has some very special metal (tiny) bits in it. An electro-magnetic valve controls the flow of the fluid. Due to the metal bits in it, its viscosity can be altered, extremely quickly.

On my Jaguar the system is always active and provides primarily anti-body roll. My X308 corners like you would not believe!!

On the X350 the dampers are switched on and off, by the suspension computer and are an integral part of the control cycle of the suspension.

Raymond talked us through endless different scenario's and how the system would react and how to troubleshoot various problems and come to a solid diagnosis.

All in all, again, another very interesting workshop. Many thanks to Raymond, Joke and Petra for all the preparations and an excellent lunch!

Jeroen

[Aditya]

Thread moved out from the Assembly Line. Thanks for sharing!

[SS80]

Hello Sir,
Wow, what an informational thread. I never knew that air suspension too has a coil and strut inside. I assumed it would be like the ones we see here in our buses, just a bellow, swing arm and anti-sway bar.

A few doubts though

Also, any specific reason why the driver is to be seated while the alignment is done?
Is there a TPMS kind of system to measure psi in those bellows?
What would happen if the compressor fails, does the car work like usual but with saggy suspension?

[Jeroen]

Originally Posted by SS80

Hello Sir,
Also, any specific reason why the driver is to be seated while the alignment is done?
Is there a TPMS kind of system to measure psi in those bellows?
What would happen if the compressor fails, does the car work like usual but with saggy suspension?

Sorry, you misunderstood. It is no use to put the driver in the driver seat during during wheel allignement. As I mentioned the compressor won’t run under 45 Km/h. Well actually, it will run, but only for max of 120 seconds due to,lack of air cooling.

So you need to activate a special alignment modes on the system, for which you need a special Jaguar tool

No there is no pressure measured as such I think. The level sensors are the primary sensors that determine how much pressure needs to go to each bellow. When the car is heavier, the bellows need more pressure etc.

When the compressor fails, the car sits down on its struts with only the 3 bar pressure remaining in each bellow as I explained earlier. You can still drive the car safely. But it won’t be wafting along of course. The ride will be harsher!

Jeroen

[Abi5hek]

Hey Jeroen, thanks for sharing this! Loved going through it.
How does one get to attend such a workshop/ technical day?

[Jeroen]

Originally Posted by Abi5hek

Hey Jeroen, thanks for sharing this! Loved going through it.
How does one get to attend such a workshop/ technical day?

Thanks much appreciated. The G&G technical days are always announced on a Jaguar forum to which they are one of the sponsors. Recently I also attended a technical day of the Mercedes Heckflosser club. I wrote about it on my “fiddling with cars thread”. Again they announce it on their forum. Most of the other technical days I attend are organised by various car clubs I belong to.

There are also a couple of car magazine that organise these events.

Plenty to choose from, but you must be tuned into the relevant social media.

Jeroen

[GTO]

Thanks for a lovely thread, Jeroen!

You've explained all the technicalities so well. From a behind-the-wheel perspective, here are my two cents on air suspensions.

Pros:

- Unmatched ride quality, especially if tuned for comfort. The W222 S-Class & previous-gen Range Rover come to mind. They are the ultimate "magic carpet" vehicles. You absolutely need air suspension in high-end luxury cars for comfort (but not handling - most sportscars don't have air suspensions).

- Can convincingly switch from comfort <-> sport modes.

- Very important for India = you can raise the suspension for tacking big speed breakers, sharply angled driveways, broken roads etc.

Cons:

- Expensive to buy

- Maintenance (pumps, leakages, plumbing etc.). Can fail unexpectedly and leave you stranded. Many S-Class owners have suffered from this. Although there are telltale signs of impending failure

- Expensive to maintain. Takes 1-lakh per corner in an S-Class in the aftermarket (that's 4-lakhs minimum every time you work on the suspension).

[Jeroen]

Originally Posted by GTO

Thanks for a lovely thread, Jeroen!

You've explained all the technicalities so well. From a behind-the-wheel perspective, here are my two cents on air suspensions.

Thanks, GTO for your additions. Some further comments.

On the Jaguar a failure in the air suspension system does not leave you stranded I believe. The car will still drive normally but will be a whole lot less comfortable.

As long as nothing breaks, there is very little maintenance on the Jaguar. At best the compressor filter and moisture trap.

But if things do break, it can get very expensive very quickly. It is one of the reasons Raymond of G&G is starting to refurbish the Jaguar struts with new bellows himself. A bellow is still an expensive item, but a fraction of the price of the complete new strut. (Jaguar only sells the complete strut).

The other thing is that these sort of cars, certainly the Jaguar, suffers from huge depreciation. Fitting very expensive parts on a car that retains its value is one thing. However fitting very expensive parts on a car with little residual value can become a problem. That is why you need a Raymond when you want to buy this car after 5-10 years, at least 100K on the clock. We could all do with a Raymond for every brand/model I guess.

I can imagine that such a system is more prone to failure in India compared to other countries, due to the harsh environment.

Jeroen

[GeeTee TSI]

On the wonderfully intriguing topic of air suspension, I ironically found this sight of a Q7 looking rather low


Probably costs an arm and a leg to fix, especially in India. The luxury is certainly for those who dare

[Jeroen]

Originally Posted by GeeTee TSI

Probably costs an arm and a leg to fix, especially in India. The luxury is certainly for those who dare

In the west, original air suspension parts are expensive. But diagnosing and replacing parts (man hours) is equally expensive and can be more expansive than the parts itself.

The latter should be considerably cheaper in India. Labour is so much cheaper. You do need knowledge of course.

Raymond is an interesting guy knowing exactly when to use original parts or aftermarket and how to overhaul original parts at a considerable cost advantage compared to complete new parts. Even when the labour cost is high, it still works out favourable.

I have seen few, if any, threads on a “Indian Raymond”. Because ai would think that would be an absolute killer combination! All that knowledge, experience and diagnostic skills at a relative low cost price point.

Are there such people in India, working on these complex high end machines? Or are you at the mercy of the Stealer/Dealer?

Jeroen

[srini1785]

I'm no big suspension guy but i work in industrial automation and use pneumatics a lot. I can tell you this much.

1. Even in a Air suspension, it is the spring that takes the load. The air bellow acts only as a damper.

2. Air bellows are used in applications where there are a lot of dynamic loads. Due to their construction they absorb both axial and radial loads within a certain limit. A 70 dia bellow produces 400N thrust at 1 bar. A piston type cylinder (Hydraulic/pneumatic) is good with axial while it is very poor with radial loads on its pistons.

3. Air scores over hydraulic (closed circuit) in one main factor. Compressibility and recovery. Hydraulic is notoriously difficult to compress (impossible) and also the recovery is slow when used in the form of a piston cylinder.

4. The original hydropneumatics suspension in a Citroen DS was a closed hermitically sealed chamber with oil either bleeding or exiting the chamber. Helium or Nitrogen was used as the gas. Even in this type of suspension, it was the oil which was the spring. The Gas was only a damper.

5. A pneumatic system is only as good as its pressure switch. If the system is interfaced to a controller using a pressure switch, then the switch is its Achilles heel. If the switch fails the whole system shuts down.

6. As much for its compressibility, Its near impossible to seal a pneumatic system for leakage. With hydraulic systems, you have to have zero leakage.

I can also say that suspension is not the only one which uses pneumatic. Luxury vehicles use Air for seat adjustment too.

[Jeroen]

Originally Posted by srini1785

I can also say that suspension is not the only one which uses pneumatic. Luxury vehicles use Air for seat adjustment too.

Thanks for all those additions.

Good to see somebody with experience in Industrial automation. When I came ashore after some 10 years at sea, I worked in Industrial automation for 6-7 years too. On board of ships, we used a lot of pneumatic equipment too.

My W123 uses a pneumatic (vacuum)system to operate the central locking system and the headlight height adjustment. If you own an automatic W123 the pneumatics are also used to control the automatic gearbox.

The valves in the AC and heating system of both my Jeep and Jaguar are pneumatically operated too!

Jeroen

[Kosfactor]

Originally Posted by srini1785

I'm no big suspension guy but i work in industrial automation and use pneumatics a lot. I can tell you this much.

1. Even in a Air suspension, it is the spring that takes the load. The air bellow acts only as a damper.

I have not seen air suspensions of cars up close, but the big buses use only the rubber bellows and a normal suspension damper especially in the rear, usually called as 'Air Bus'.

[Jeroen]

Originally Posted by Kosfactor

I have not seen air suspensions of cars up close, but the big buses use only the rubber bellows and a normal suspension damper especially in the rear, usually called as 'Air Bus'.

I think many types of trucks use similar systems as this Air bus as well.

Jeroen

[androdev]

Here is a very detailed documentation of Airmatic in Mercedes-Benz W220:

https://w220.wiki/Airmatic

The weight of the vehicle is carried by the compressed air sealed into the air bag/bladder of the air springs. This is what makes it possible to raise or lower the vehicle by changing the air pressure.

Air Suspension is probably the single most reason for the crazy depreciation of high end luxury cars like S Class. Not surprisingly, the designs have not been improved to offer better repairability as the struts have no replaceable child parts. Dust boot covers are really flimsy and once damaged (torn), lets in all type of contaminants which accelerates the damage of the air bellows. There is no way to replace these dust boot covers. Air bellows are the most common failures that render the suspension unusable and once again, these are not serviceable items.

Even an undergrad student can suggest vast improvements to the air suspension for longevity and repairability but I guess the manufacturers prefer the current arrangement of these luxury cars having a short service life.

Does the availability of cheap labour in India make the repairs cost effective? Not really because the workforce skill levels are so inadequate, it would be a miracle if someone fixed your shower the first time. The kind of eco system and culture we have here is to source the cheapest parts from China and use a sledge hammer and crowbar to fix things up.