I recently got two front air struts from a junked 2005 Ultra Luxury. How do I evaluate them prior to installation to see if they are fully functional? Neither had large oil leaks, though both had a little bit of oil come out of the air line when I first compressed the suspension. One of the struts compresses and decompresses slowly, while the other one does not compress at all when pushing on it with my body weight.

I saw this YouTube video showing an air strut test but it does not say if the strut was behaving properly and if not, why not.


Any insight would be appreciated.

 

That looks like it's behaving normally. If you have one that you cannot compress at all, check that the air line isn't blocked.
Otherwise it may be seized so may require more weight to free it up.
Once under air-pressure the strut will behave like a normal coil-over.

Air-suspension is simple to understand.
All it does is replace the spring with an air-bag that behaves like a spring when under pressure, and often they have a weaker coil spring in addition to the air-bag.
Higher pressure = higher preload and higher ride height.
Where it gets complicated is in the computers that control it, not in the strut itself.
The LS430 air-strut has computer controlled preload/ride-height and damping.

 

Thanks. Is a little bit of oil coming out of the air line (as I compress the cylinder) normal?

 

No, it's not normal, the struts are on the way out.

1. Compressed and expand the pneumatic shock absorber cylinder assembly 4 times or more. See attached
2. Check that there is no abnormal resistance or unusual operation sounds.
3. Check that there is a difference in the damping force when the rod is positioned as shown. See attached
If there is any abnormality, replace the pneumatic shock absorber cylinder assembly

 

I would never put used struts on my car. The damping response is reduced over time, with or without any oil leaks which should not be present. How many miles did the donor vehicle have on those struts? I’d pass on installing those and get some brand new ones from Impex Japan at 1/3 of the cost of retail.

 

Why does the damping response reduce over time even without oil leaks?

I’m debating whether to buy a pair of good condition used struts with no leaks from VIPsusha for ~$400 or a pair of brand new struts from Impex Japan for ~$1500.

 

The internal hydraulic will lose its ability to dampen over time like a regular strut. I just pulled two rear off my car, neither were leaking but one was totally blown internally and the ride was awful, very bouncy and jarring over any bumps. The other still had some force when pressed on but it was starting to sag while parked and knew it was also time to replace before the ride went to hell on that side too. They were 20 and 14 years old. The air bag itself can still hold air and whatnot but if the rest of it is shot then it’s also bad. I’d go for new. If you buy used you just paid a lot in labor (for rears, less for fronts) and will have to redo it sooner and the ride quality will not be the same as new.

 

For point 3, if the rod is at, say, 12 o'clock, and you rotate 360 degrees and end up at 12 o'clock again -- is the damping unchanged? Or does the damping continually increase/decrease as you rotate greater than 1 revolution?