airbag suspension very weird issue

[Homerlovesbeer]

Hi all,

I've got a 4.8is with self levelling airbag suspension on all corners. The car goes through all 3 levels just fine and normally just works. Today I had a really really weird thing happen.

We went away for an overnight trip around 150km from home. No dramas until today we were doing 100Km/h down the highway. The road wasn't great however the ride suddenly turned to poo with the car bouncing all over the shop. I turned to my wife and said "I think the airbag suspension has failed" and pulled into a rest stop.

I could hear hissing coming from the rear of the car and sure enough both rear wheels were down low in the arches. After a few seconds the hissing stopped which I assume was when the pump stopped. I tried raising the car with the result being the hissing starting again, going for about 10 seconds then stopping with no change in ride height.

I grabbed a torch and got as far under the rear right side of the car as practical (hoping the car wouldn't suddenly jump into gear and run over me or the wife kills me hahaha kidding!) and asked the other half to try raising the car again. Same result, hissing which stopped but no airbag inflation.

A quick google search suggested a split airbag which I thought was the drivers side (RHD car). So far from home we thought about a tow and realised it wasn't really practical as they would tow us to the nearest garage, not home, and we'd be stuck.

So we elected to drive rather slowly along typical Australian country roads trying not to bounce our way off the road.

Making it home I parked the car in the garage and started to look at replacement airbags. After a while I thought I should look at exactly where the air is escaping from so I went back out to the garage and was going to drive the rear up a set of ramps so I could crawl under and have a better view.

The car was so low the ramp couldn't get under the car so I thought if I could get a couple of cm's of lift that would work so I started the car. The car hissed again for a few seconds then suddenly stopped at the airbags inflated like normal!

I was like "what the hell?"

I then went through all the heights, lowered to the lowest setting, raised to the highest, back to normal, low, hight etc a few times. No hissing, no sag nothing, just normal operation!

I have no idea what's going on and what failed or malfunctioned on the drive.

Does anyone have any ideas?

I can't even check for air leaks now as it's fixed itself!

Cheers

[andrewwynn]

I've had an air spring* fail on a fold that would occasionally pinch itself closed and function again until it didn't. They are folded in half so there's a big zone that's pressed firmly into a hard u-turn that can pinch a leak closed. That's my bet.

[Homerlovesbeer]

Wouldn't that open up again at full height though?

I was wondering if it was actually a pressure relief valve that got stuck open and after being parked for a while cooled and then unstuck itself?

Edit: Also why would both rear bags not inflate? The whole rear axle was on it's arse not just one side.

The front axle didn't change (was normal) but also wouldn't go up/down either.

[andrewwynn]

There are good schematics of the system and I think you can see almost everything for the rear axle under the trunk floor that comes off.

I had one axle system so didn't have height adjustment. Depending exactly where the leak I suspect it can hold at all heights. It's definitely tricky when a problem goes intermittent.

Too bad you didn't lift there trunk floor while it was hissing.

[Homerlovesbeer]

Hmmm

I didn't bother because it sounded external

[bcredliner]

First, scan for trouble codes, that can indicate the problem or provide some insight, Verify the compressor is running. If so, use the age old troubleshooting method of soap bubbles starting from the compressor. Follow the lines to the air suspension "bags". In some circumstances the troubleshooting won't expose the problem necessitating re-setting the factory levels using a scanner. You can also use the scanner before troubleshooting for leaks.

[andrewwynn]

Scanner will deflate and reflate (sic) to give you opportunity to check. Odds are at least 95% it's the spring.

[Homerlovesbeer]

Hmm ok so that's todays job.......

Crap

[Homerlovesbeer]

So I tried driving the car again, bags went flat after a km. Seems andrewwynn was probably right. Took the car to a couple of suspension places but too busy to even take a look until Friday.

Stuff it, I'm just going to buy 2 new rear bags.

Next thing, what brand?

I know Arnotts seems popular but I can also get Sachs bags, Bilstein, etc

What to buy?

[crystalworks]

No experience on the E53 (switched to coilovers after faffing with the 2axle air for longer than I was happy with, and began to question it's reliability) but on our E61 the Arnott bags have worked well.