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Faulty air spring design

 
Old 04-17-2019, 10:00 AM
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Default Faulty air spring design

Hi All,

I have made an interesting, if not startling, discovery with regards to the Arnott replacement front air springs for the Allroad.

After the OEM's air springs failed on my vehicle I purchased the Arnott front air springs.

Over a period of 4 years and 50000 miles the vehicle has been through no less than 5 Arnott air springs. All the air springs failed suddenly. The car would be fine one day and the next day it would drop right down within a matter of minutes and the air springs would then need to be replaced. , i.e. no slow leak type scenario's.

When the last one failed I noticed that the vehicle was resting on the control arms and the vehicle was not driveable as the wheels would rub against the arches when the steering is turned.

The air spring airlines also got damaged in the process as they got pinched by the control arms pressing them against the fender.

This seemed strange to me as I did not experience this when the OEM air springs failed and was able to still drive the car to a workshop or home.

I ordered a new Arnott air spring and upon closer inspection established that the bump stop in the Arnott air sping is 40% shorter (60 mm long) vs the OEM bump stop (100mm long).

This explains why the vehicle was resting on the control arms as the Arnott bump stop is not long enough to support the load of the vehicle which is what it is supposed to do.

More alarming is the fact that the bump stop is a very important safety component that is designed to ensure the vehicle remains stable on the road when the suspension is under maximum compression. If during hard cornering the bump stop does not support the side under compression it can cause instability and an unpredictable behaviour of the vehicle which can cause the driver to lose control.

Even worse imagine a scenario where an air spring fails during high speed cornering resulting in the wheel rubbing against the fender. This can induce a sudden oversteer and resultant loss of control of the vehicle.

I also believe the sudden failures I have had are a result of the air spring having to do many more high compress cycles than it should due to the fact that it does not have an adequate bump stop to support it. See pic of failed air bellow reflecting the catastrophic failure!

I have enquired with Arnott about this alarming design fault. They have however not even bothered to revert with an explanation.

I sent the Arnott air spring back as it is clearly not fit for purpose.

I would be interested to hear what other peoples experiences have been on this.


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Old 04-26-2019, 04:54 AM
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What's your part number?

Arnott makes a spring with a metal shield over the airbag. Yours appears to be the early one.
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Old 04-29-2019, 05:29 AM
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Hi shanechevelle,

The Arnott air spring model you are referring to has a different spring rate which is achieved by using the metal band.

The model I am referring to is the A-2869 which uses the same spring rate as the OEM.

Both these models are current
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Old 06-03-2019, 09:43 AM
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Arnott does use a bump stop that is slightly smaller than the OE. During the original design we used the same size and material as the OE but the ride was a bit harsh.To fix this engineers changed the bump stop to a polyurethane unit that was a bit shorter but improved the ride quality significantly. We have sold these for well over a decade and typically this is not a problem.

Arnott Customer Support & the R&D team note that main reason for this type of damage is if the vehicle is driven in a deflated state for a period of time. Driving conditions, add-on modifications and mileage may also affect this. Regardless of the cause - we apologize for your continued issues - Please contact Customer Support for a warranty replacement.

We offer a Limited Lifetime Warranty in North America for all of our allroad products including GEN I & GEN II Air Springs, our new pre-assembled complete struts and the Arnott coil spring conversion kit which should eliminate future air suspension related issues on these 14+ year old applications.

Arnott Parts for the 2001-2005 allroad: https://www.arnottindustries.com/pro...5-chassis/2004




Last edited by ArnottDoug; 06-05-2019 at 11:44 AM.
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Old 06-04-2019, 10:55 AM
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You must really love your allroad to put up with five replacements, all of which I assume were covered by Arnott's warranty. I purchased one of their first coil spring conversion kits, and have never had to worry about suspension troubles again. Yes the ride height is a little lower (I would think they could fix that) but I don't really have a need for or miss the height adjustments.
Just a thought.
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Old 06-11-2019, 09:05 AM
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Originally Posted by ArnottDoug View Post
Arnott does use a bump stop that is slightly smaller than the OE. During the original design we used the same size and material as the OE but the ride was a bit harsh.To fix this engineers changed the bump stop to a polyurethane unit that was a bit shorter but improved the ride quality significantly. We have sold these for well over a decade and typically this is not a problem.

Arnott Customer Support & the R&D team note that main reason for this type of damage is if the vehicle is driven in a deflated state for a period of time. Driving conditions, add-on modifications and mileage may also affect this. Regardless of the cause - we apologize for your continued issues - Please contact Customer Support for a warranty replacement.

We offer a Limited Lifetime Warranty in North America for all of our allroad products including GEN I & GEN II Air Springs, our new pre-assembled complete struts and the Arnott coil spring conversion kit which should eliminate future air suspension related issues on these 14+ year old applications.

Arnott Parts for the 2001-2005 allroad: https://www.arnottindustries.com/pro...5-chassis/2004
Hi ArnottDoug, Thanks for the feedback.

I have contacted customer support, however they have failed to respond to my e-mails re the defective design........ I live outside the US so the lifetime warranty does not apply. Total cost to me so far to replace the 6 airsprings is in the region of $3000!

The airspring ultimately was not designed to run a shorter bump stop. Running a shorter bump stop is a bit like suggesting one should underinflate tyres for a softer ride. It will work but we all know the dangers and damage done to the tyre by running them underinflated! Ditto for running a bump stop that is too short.

If the bumps stop was the correct length there would not be issues with driving the vehicle to the closest place of safety without damage
If the bump stop was the correct length there would not be damaged air lines due to the vehicle resting on the airlines where it should be resting on the bump stops.
If the bump stop was the correct length many of us users would not have premature failure and leaking of the air bag around around the lower connecting ring.

I never drove the vehicle as is suggested on deflated bags to then cause the damage. I parked the vehicle in the evening on level 2, came back the next morning to find the front completely deflated. It had failed so badly over night (whilst standing in the garage) that I was unable to even raise the vehicle at all the following morning

The bump stop is 40% shorter which is somewhat more than "a bit" as suggested. Note that this % is based on the full length of the bump stop including the portion integrated into the top support. If however you base the difference only on the active (protruding) portion of the bump stop the difference is probably closer to 60%.

I am seeing multiple symptoms (tyres touch fenders, airlines damaged, vehicle resting on control arms, multiple failure of airspring at bottom connection ring) on my side that all point to one cause and that is that the bump stop is too short.
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Old 06-11-2019, 09:33 AM
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Originally Posted by B7JDS View Post
You must really love your allroad to put up with five replacements, all of which I assume were covered by Arnott's warranty. I purchased one of their first coil spring conversion kits, and have never had to worry about suspension troubles again. Yes the ride height is a little lower (I would think they could fix that) but I don't really have a need for or miss the height adjustments.
Just a thought.
Hi B7JDS,

I am outside the US so my Arnott's were not covered by the lifetime warranty. Totals cost so far is in the region of $3000! In hindsight I should have just replaced with OEM's when the original OEM's failed. But as they say hindsight is an exact science!

I did consider coil springs. I however do enjoy the smooth ride of airsprings and feel the adjustable airsprings are a unique character of the allroad for me.

Thank you for the heads up though!
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