A few q's about the air ride system

[calisonic]

Iv'e read the post in the maintenance section and it helped me understand the basics of the height adjustment system but I have some lingering questions.

1) When I pull out of my drive way and start off down the road, I can usually hear a slight "piff" noise, coming from the back of the car as soon as I hit about 14 mph. This noise sounds like an air bag venting, (like on a bagged low rider but much quieter) at first I thought it was just something sliding around in the trunk as I was told the airbag system is designed to be too quiet to actually hear the bags venting. However, I completely cleaned out all non-bolted down objects in the car and can still hear this, even with the air ride switch off.

2) My suspicions in the above statement is supported by the fact that even if the air ride switch is off for as much as two weeks of daily driving, the rear of the car will be sitting significantly lower than the front, but if the car is parked for that same period of time, there is nearly no difference in ride height, front or rear.

3) My mark VIII's compressor will run even if I don't exceed ~63 mph, in city driving every 5 minutes or so, for about 5-7 seconds, when I come to a stop. However I don't believe there is a leak, (lest not a significant one) because the cars ride height won't change after two weeks of not being driven.

Any ideas?
Thanx.

 

[whiplash15]

I hope this makes sense to you. Bags USUALLY leak somewhere other than properly inflated. In other words, when the strut is at less than normal ride height. That would explain why you hear the release of air after just coming out of the driveway. It also is the reason the compressor runs on the highway. The struts are lowered to the highway height which is an inch or so lower than the under 45 mph height. (parked height) In any case, the venting is done thru the compressor, not back by the rear bags. I would say you have one or both bags in the rear leaking. Also, if you drive the car, shut it off, close the drivers door, the system gets the signal to lower the car to parked height. If you then shut the air ride switch off, its already too late. The car will drop to parked height exposing the bag leak, and the result is a slamed rear end. If you leave the car run, shut the airride switch off, then shut the ignition off, and then close the drivers door, NOTHING happens.. The car stays at normal ride height, so the leak is not exposed and the system remains up. Hope this helps.

 

[calisonic]

it does thanks.

 

[billcu]

That noise that you are hearing might be the ABS system. It makes a funny noise like that which is normal, when first driving the car.

 

[tixer]

I know this noise you are referring to. Almost like a tire slips a fraction of an inch or something. My 1997 does the same thing. I've noticed it, but never made an effort to track it down. Glad I'm not the only one. the ABS thought had occorred to me. I'd also wondered if there was perhaps some play in the diff after going from reverse to forward or something. Bill: do you know what the ABS is doing in the scenario you described above?

 

[Roadboss]

As explained above your air springs are probably leaking. They usually develope small hair line cracks around the folds due to the rubber drying out and rotting. These cracks are microscopic and explose themselves as the rubber flexes. Fortunately the rears are rather cheap and easy to replace. I would get them replaced soon so as not to overwork your compressor. American Air Suspensions is a great place for all of our air ride components, and Eddie is tops with customer service and advice.

http://www.americanairsuspension.com/cart/products.php?cat=3

 

[tixer]

Got it: Thanks. I should have read more carefully. I honestly never attributed it to the suspension. The compressor always ran at just the right times, and I've never had any trouble with "slamming." Perhaps I'm at the very beginning of the end.

 

[Roadboss]

They are not that expensive and if you consider how long they have lasted, and the service they do during operation they are justified. Just need to be considered as a maintance item (every 8-10 years).

 

[tixer]

I'll have to check my records to see when they were replaced last. (work performed by the previous owner) I actually just got the car out of storage last night, and had the rear wheels off to check things out. The rubber looked real good, and they were still holding air. Of course I've read here that the visible parts aren't usually where the leaks occur. I also found myself wondering if I ought to replace the shocks.. I don't know when those were done last.

 

[billcu]

I'm not sure what that ABS noise is but I never noticed it in my 94's. I'm guessing it's some kind of reset/test?

It has nothing to do with these air ride problems though.

My red 94 is starting to leak in the rear airsprings (imagine that, only 205K miles and 15 years old.).

It only leaks at parked height, so I've been adjusting it above that with my module, and turning the switch off until I get a chance to fix it.

 

[calisonic]

why would the ABS make such a noise though?

 

[billcu]

I don't know, but I checked it again yesterday on the way to work. It seems to only happen when the car is cold, and it happens when you first hit 13 or 14 mph.

 

[MindyMark]

The ABS goes through 2 self tests, one right after start up (you can watch it complete when the ABS light goes off), the second one is supposed to occur around 11 to 14 mph, where the ABS pump runs for a second. This is most likely the noise you hear when shortly after leaving. If the car only makes the noise once after starting the car, I really doubt your air suspension is to blame.

 

[tixer]

That does sound a bit more like my own experience. However, I'd say the noise is closer to 3mph than 11.. just after you switch from reverse to forward, and start to roll. Now I'll have to pay closer attention!