garrett376

I wanted to clarify some points about the 958 air suspension for those interested. And I have no disclosures to state!

First, there is currently a way to fix your leaking air suspension struts with lifetime parts. Yes, lifetime warranty parts so you can be assured these will be the last struts you need to buy (even the front right where the OEM seems to last only a few years). There are a couple air suspension replacements available on the market, but only those available through Arnott Industries provides a lifetime warranty. Arnott has a rebuilt OEM option for about $1000 per shock plus a core charge, or a new Eibach shock-based replacement for about $800 per shock where a core is usually not charged. When no core is charged by the reseller, Arnott currently gives you back $90 per strut with a pre-paid shipping label so you can easily box up your old strut and ship it out. For some reason, the new Eibach-based shock does not have mounting holes for the plastic deflector panel to mount back on the strut; the OEM has holes in the strut's fork to mount the deflector. So you will either need to leave it off, or find a way to mount it by drilling holes in the fork, or coming up with some other creative solution to mount it. I've reached out to Arnott to determine if the warranty is affected by drilling the holes but have not yet heard back on that.

Replacing the struts is really quite simple, especially if you've replaced struts on any other kind of 911. This video shows the process:


Some points not clear for those that haven't done this: Since the suspension uses an "air spring" you do not need spring compressors to get the job done and withdraw it from the wheel well. To do the job without losing your nitrogen, and to be able to "compress the air spring," you will need a capable scanner like a Launch x431 V+. Using the Launch, it is possible to withdraw all of the nitrogen from one strut at a time. I have a 2014 version PIWIS2 and it was only able to bleed one entire axle at a time, but the Launch was able to do one strut at a time. Using the Launch, in the Level Control/PASM section, in the Special Function section, under Replacing an Air Strut, is the function to bleed one strut at a time. Using this function, the strut's nitrogen is withdrawn into the system's on-board accumulator. So once you withdraw the nitrogen, you can now undo the air line to the shock, and all you lose is the insignificant amount of nitrogen in the air supply line. I found it actually works best to run the "bleed" function twice to drain the individual strut so you know you've got it totally emptied. You can tell by pressing on the exposed part of the air bag near the top of the strut - it gets quite soft when it's drained. Now, replace the shock by undoing its mountings like the Bilstein video shows. If you have PDCC and you are close to being due for a replacement reservoir, now is the time to replace that reservoir since it's tougher to work around leaving it installed. Once the new strut is installed, you can either use the Launch's functions to refill the strut from the accumulator's pressure, or you can just use the rocker switch on the console to remove the system from Jack Mode, select a higher height (with the door closed and Cayenne still off the ground on that corner), and it will fill the strut by itself. Once it's been filled, you can move on to the next side.

The workshop manual requires a new bolt and new nut on the lower control arm:

• Lower Control Arm Bolt - Porsche (PAF-105-326)
• Lower Control Arm Nut - Porsche (PAF-103-353)

Get them ahead of time from a discounting dealer, or you'll need to get it from your local dealer, which in my case, doubles the price of parts and then my PCA discount graciously returns the parts to the MSRP. The strut comes with new nuts for the top of the strut, and a new air line fitting and crush ring. As indicated in the Bilstein video, be sure to measure your Normal Height distance from the fender to the wheel centerline, since the lower control arm bolt is torqued at that level. It's easy when the strut is partially filled to compress the entire suspension to permit torquing of this bolt (111ftlb plus 90º) at the correct control arm/suspension position.

What if you've lost nitrogen over time? It is not published that I could find, but the system will run at a lower pressure level without pulling in outside air and without errors or functional problems. The system is supposed to have a minimum pressure of 10bar at Normal Height, up to a max of 17 bar. Most Cayenne's I've seen run around 6-9bar, with no functional issues. The Launch provides you a way, under the Measured Values section (Launch spells it Meas.vals), to see what the system pressure is at whichever height you are at. If you've lost all the nitrogen in the system, or are concerned you've been running without a purely N2 filled system, then you are going to need to pay the dealer to vent/purge the system and refill, or you can buy the supplies yourself for about $3-400 and use a tester like the Launch to do the vent and refill, to reach the specified 10bar level. Or if you're just low, you can top off the system at the accumulator until you reach the 10bar level at Normal height while monitoring the System Pressure in the tester's Actual Values (or Data Stream with Launch).

And finally, if you're replacing your struts, which means you likely have some miles on your 958, now is the time to replace your upper control arms. You cannot replace them without removing the strut. Note that the manual requires new mounting bolts since you'll be torquing the heck out of them: 37 ftlb plus 180º!

In summary I hope this his helpful and clarifies some points about the air suspension. Folks on here sometimes mention they fear buying a Cayenne with air suspension due to its "issues" but it's very reliable and if you catch a leaking strut early enough, the replacement process is quite easy and you can end up with a lifetime replacement solution thanks to Arnott's current offerings.

lml999

Thanks, this is very helpful!

RS-America

Excellent post - should be pinned!
Wondering when to consider having our struts done or what degradation to look for first. Concern is having a failure off-road on trail where it would not be driveable to reach assistance. We have really exercised our 2013 Diesel with 112k miles of mainly off-road and endurance rally where we use our air suspension a lot. Lots of different environments driving from the hot Chihuahuan desert up to the frozen Arctic Ocean where temps got to -40F, 60mph winds, blizzard, -90F windchill.
Yesterday took our CD to Dirtfish for some mud and wading through the water experience. WRC drivers like Ken Block, Travis Pastrana, and Sébastien Loeb have all had fun driving at DirtFish. They are developing a 4x4 course that we both got to drive Saturday. Lots of fun - Many different rigs, four Cayennes ran yesterday - P!Gs in their element - MUD. Got home in time to hose 'Otis' down and watch the last of Sebring. Photos at link-
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https://rennlist.com/forums/cayenne-...meet-otis.html

deilenberger

Garrett - I was playing with the Foxwell NT530 with Porsche module this afternoon, and stumbling around the air-suspension part of it - there are functions to pump the nitrogen out of any air-spring into the reservoir, and then refill the spring when it's been replaced. It also offers bleeding the system by axle, and corner height adjustment.. not bad for $155 tool. I didn't try the functions since my suspension is working - but it might be interesting to try it if someone in the NJ area was thinking of replacing air-springs.

24678923

edit: see this thread for more discussion on the Arnotts

Lolomds

Bonjour garrett376,
Tout d'abord merci pour ton article très intéressant sur les amortisseurs pneumatiques.
Je me permets de te poser une question.
J'ai cela comme valeur de suspension

Avant droit: 5.470 bar
Avant gauche: 7.440 bar
arrière droit 5.470
arrière gauche 2.640
Pression dans le système: 9.300 bar
Je n'arrive pas à comprendre ces valeurs et j'ai l'avant qui a tendance à rester bas et flotte

Merci pour ton aide

thomas311

Hi Garrett @garrett376
I was reading several of your posts about the Cayenne air suspension. I have a 2012 CT. And I just got my front struts replaced in a shop due to front left leaking. I went with Arnott 3056 and 3057 (the reman ones) and ordered myself from FCP due to the lifetime warranty. Then I tasked a local shop to install them. Picking it up at the shop I verified raising and lowering the struts and it worked. Driving home a big gun-shot style noise appeared and both front struts collapsed instantly and simultaneously to the bottom. Arnott is sending me new struts under warranty, but the installation is not covered. I do quiet some work on engine and suspension and electric on my older Mercedes, so I'm pretty handy and consider doing this job myself now. I studied the Arnott installation manuals and watched the Bilstein video a few times.
I cannot measure normal ride height anymore as my car is completely deflated up front. So what would be the values on all four? I have a youcanic scanner but I need to figure out what functionality is provided for the suspension. But if it does not support it, what's the safe way to lower the car after install, and re-inflate the strut? I do understand the video and your above comments. I think I have to reinstall both struts first before i can actually get any air into the system. So how do i figure out how low i 'jack it down' before starting the car, select high position, let it refill and then lower it onto its own wheels?
Thank you for clarifying this process a bit more for me.

garrett376

Hi Thomas,
The normal ride height for a CT is around 17.5" from the wheel center to the fender. So do your install of empty struts, torque the mounting bolts (sway bar and lower strut mount) at that 17.5" height, then put on the wheels on, and lower the car to reach about a 17" level. Hook up the nitrogen tank at about 250psi to fill the accumulator, then start the car, and select high level 1 to raise it up off the jacks. If you go all the way up to high level 2 with the nitrogen tank still hooked up, you'll overfill the system which just wastes nitrogen as you'll hear it vent when it comes back to normal level. So raise to high level 1, unhook the nitrogen bottle and your'e done.

As an aside, unless your labor is free, and you don't mind buying new hardware on a frequent basis (they are single use bolts on the lower sway bar and control arm mounting), I don't see the benefit of going with ANY strut other than OE from Porsche. I don't see the point going with less reliable aftermarket parts unless you can do everything yourself and enjoy the replacement process.

thomas311

@garrett376 Thank you that is very helpful and clear. Regarding your note about after market parts vs OEM Porsche: I don't think you can get new struts from Porsche anymore, only parts to do your own rebuild. That's why I went with Arnott as they are rebuilt Porsche struts. Looking at your first post in this thread, I thought you recommended them. The problem I'm facing is the rear struts. One of them is developing a leak too and Arnott does not offer rebuilt struts for the rear anymore. They only offer their own new model which does not support PASM. Switching all 4 to Febi is currently no option either as the rear ones are mostly unavailable. Another option is using RMT rebuilt ones, but I'm a bit concerned about their reputation. Some people like them, some made bad experience....but with their rebuilt struts I would be able to keep PASM. Or I go Arnott without PASM. What would be your choice?
Regarding the Nitrogen fill: some people seem to use Nitrogen some seem to not bother. I take it you always use Nitrogen. I'm currently not setup to do this, and I think before I charge the system with Nitrogen, I should have all 4 struts replaced making sure all leaks are gone. I don't have equipment to charge Nitrogen myself, but I would consider getting it with some guidance. But first I need to get the car "off its knees" again. Is there any harm to just use the onboard pump to refill the struts and get the car drivable again, fix the rear ones asap and then swap to Nitrogen?
Thank you for your kind support and sharing of expertise!

One more thing: I still have the original Porsche struts which just came off the car: i can send them to FCP to get $400 core charge back, or I can keep them and maybe rebuild myself or also send them to RMT? What's your take on this?

garrett376

I've learned over the years on too many Cayennes since that original post: at this point I would only go with Porsche parts if you want the most reliable/proven long term solution. While Arnott/FCP may provide a lifetime warranty, the parts are far from lifetime and I have too much other fun stuff to do, to be swapping struts due to early failures, regardless of whether the manufacturer states it has a warranty.

While it's true you can't buy the entire OE strut as a single part number, it's not difficult to buy every piece needed from Porsche to create your own new strut - all of those parts are available from the dealer and discounting shipping dealers like Gaudin. 99% of the time the shocks are just fine and you just need the air spring components of the strut anyway.

Regarding nitrogen: it's a 30 minute trip to an Airgas dealer for a small steel cylinder tank of grade 2 or food grade nitrogen (my local Airgas doesn't carry the expensive grade 5 or the expensive special cylinders for that gas, and thus our local dealer uses only grade 2 as well), and then a relatively inexpensive Amazon purchase of the regulator and tank fittings, then you're equipped to fix things, and re-fix things (especially if you get non-OE parts ).

Considering the unnecessary cost of burning up your pump, I personally would not let the pump fill an empty system. It's purpose built to shuffle around the air, not fill an entirely empty system. You'd be taking quite a few life cycles out of it doing that when you should just get a nitrogen tank and fill it, which it sounds like you'd rather do in the end! Head to your local Airgas and order up some Amazon parts!

thomas311

@garrett376 So I just placed a few calls and found 40 cubic feet bottle (smallest they had) of grade 5 at around $125 plus bottle rent or purchase. Regular grade would be $28. Is it worth to go for grade 5?
How much do I need for a full fill/flush of the cars system?
Can you help me with the regulator and tank fittings topic? They said the bottle fits a standard regulator, but I don't know what I need to plug it into the cars system and how to plug it in there.

As per the OEM part topic: should I keep the old OEM struts and rebuild myself? Do you happen to have the full list of parts needed?
Thank you so much, all of your input is awesome!

Also: do you have the rear strut torque specs and maybe the bolts which need replacement (if any)?

thomas311

I think I found out what's needed to connect the Nitrogen tank to the cars accumulator: and

thomas311

@garrett376 Hi Garrett, sorry to bother you again. I found all the torque values in some other threads you contributed (Thank you so much) except for the air tube to strut valve fitting. What's the correct torque there? I also have now a list of parts needed for the rear struts (also thanks to another thread you contributed) and I got already quotes from some parts dealer for OEM Porsche parts. That will be next on my list once the front struts are done. I will keep the old front struts to rebuild them as well later if the Arnotts fail. Do you have a link or a list for parts required for the front rebuild?

garrett376

I don't have a torque value, nor do I think it is even listed with AllData. It's one of those fasteners like a brake bleeder screw: I've never torqued one of those to a specific setting, either. Just tightened by feel.

Regarding a front strut parts list, just call the dealer and they'll be able to give you all the parts, or look at the dealer websites online and they list them all there.

thomas311

Thank you Garrett, all set on the front struts. Both replaced and system refilled with Nitrogen. I used the Foxwell NT530 to help with refilling and leveling the car. After a height sensor calibration the car now sits nice and level on all 4 corners and drives smooth and quiet. Now on to the rear struts rebuild process once I receive the parts. I can clearly hear the left rear leaking when i go to one level above medium (normal). The leak appears to be very minimal when in normal or low level.