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Unread 12-01-2010, 06:42 PM   #16
ecupip
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Does't sound like you have owned any of them long enough for any failures. I know for a fact the Touareg and Cayeene do not have closed suspension systems. They pull outside air in and compress it for the system. Audi I would beat is the same way. All of those models all anyone needs to do it google air suspension and there are tons of people on forums complaining about issues.

The 2011 Cayenne has moved to the closed system like the Jeep, no word on the 2011 Touareg yet. All of which will be a catastrophic failure if any air leaks out.

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Unread 12-01-2010, 08:25 PM   #17
mjw930
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Yes, there have been some failures, mostly from the corrosion of the air inlets on the front struts and yes, they aren't cheap to repair. However, your assertion that the "closed" system on the Jeep would have a catastrophic failure it there was a leak isn't accurate nor is the assumption that the systems on the Cayenne/Touareg/Q7 are "open" systems in the traditional sense of the term. Closed refers to the way air is channeled to and from the shocks. In the slightly older systems used on the pre-2011 Porsche/VW/Audi pressurized air to the shocks is managed through a manifold system fed from a pressure tank. The "pump" is used to pressurize the tank, not the shocks. On a traditional "open" system atmospheric air is used to pressurize the shocks so it can't react to fast, minute changes. The major difference is the way they dump waste air. The older systems vent to atmosphere which means repeated actuation results in the potential to exhaust the pressure supply and the system has to wait for the tank to be filled by the pump. The Jeep, OTOH, "pumps" the air back to the tank from the shocks. It has to pump the air because the tank must always be at a higher pressure than the shocks. On any system a failure in the system can cause a failure if it occurs within the air bladder. If it occurs in the lines or the tank there are check valves that will close off and prevent a suspension collapse. Air leaking out isn't a problem either, they all draw atmospheric air to recharge the tank if the pressure falls below a certain point. You can purge the tank and the system will refill it through a one way valve.

You can argue all day which system is better and whether it's reliable but that's academic IMHO.

However, if you are someone who will purchase a GC and run it well past warranty then perhaps the air suspension is not for you. Of course no one knows if you can retrofit the metal suspension but based on what I see visually I think that would be a very easy modification many years and many thousand miles down the road. And of course like any other technology it's something more that can break.

Sounds like if you don't want air suspension then an OL isn't for you though I found at least 1 at a local dealer that was early production and does not have QL so if you look hard you may be able to find one.
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Unread 12-02-2010, 01:43 PM   #18
ecupip
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Quote:
Originally Posted by mjw930 View Post
Ye Air leaking out isn't a problem either, they all draw atmospheric air to recharge the tank if the pressure falls below a certain point. You can purge the tank and the system will refill it through a one way valve.
Not on the Jeeps you can't it is a CLOSED system meaning the compressor is unable to draw in atmospheric air to pressurize the system. It is filled with Class 5 99.999% pure nitrogen. If you loose the air the system can not replenish itself.

Jeep Grand Cherokee WK2 - Quadra-Lift Air Suspension system
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Unread 12-02-2010, 06:17 PM   #19
mjw930
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Quote:
Originally Posted by ecupip View Post
Not on the Jeeps you can't it is a CLOSED system meaning the compressor is unable to draw in atmospheric air to pressurize the system. It is filled with Class 5 99.999% pure nitrogen. If you loose the air the system can not replenish itself.

Jeep Grand Cherokee WK2 - Quadra-Lift Air Suspension system
I stand corrected, I was reading more generic information regarding the new generation of air suspensions.

See page 15 of the following link: http://www.vehicledynamics-expo.com/...rotendorst.pdf

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