AHC: Various Early Signs of Failure?

[Tinkerer]

Anyone care to comment on the various signs of failure of the AHC suspension system?

I recently changed the AHC fluid on my '99 LX470 at 96k miles. Now, after a few weeks with new fluid, the suspension character seems to be changed: The roughness & small bumps are better absorbed, as if the "stiction" has been reduced. But also, the rear seems as if the spring rate is reduced - the rear travels more, for a large bump or dip, than the front. It doesn't bounce repeatedly, so the damping seems OK - it just seems like it has "softer springs" (lower spring rate) than the front.

It's possible I didn't get all the air out of the system when I bled it, so I'm going to redo it with a couple more cans of AHC fluid.

But I'm also wondering if anyone has experienced this sort of change ("softening") as a sign of impending failure of actuators or other component.

TIA.

 

[tabraha]

I could be wrong, but the new fluid should make it feel softer. The old fluid doesn't possess the good fluid dynamics like the new fluid and will harshen the ride very gradually. When I changed my fluid I noticed my ride gradually softened up too as the new fluid worked it's way through the system. If you're like me (bought mine used) you don't know what your LX rode like when new so it would seem different and could be percieved as something wrong. Just my thoughts.

 

[Tinkerer]

I could be wrong, but the new fluid should make it feel softer. The old fluid doesn't possess the good fluid dynamics like the new fluid and will harshen the ride very gradually. When I changed my fluid I noticed my ride gradually softened up too as the new fluid worked it's way through the system. If you're like me (bought mine used) you don't know what your LX rode like when new so it would seem different and could be percieved as something wrong. Just my thoughts.

I believe you are correct. I bought this LX new, but the change is so gradual you don't really notice it over time. However, at 90k+ miles, I was in fact noticing that rough road surfaces and tiny bumps seemed to be harsher than they should be, even when the suspension was set to soft ("Comfort"). And now, the new fluid is indeed softening the rough surfaces and tiny bumps.

My concern now is that the rear seems to be softer than the front. It may be that the new fluid will gradually "soften" up the front some more also, or that there is some residual air in the rear. Or it may be the first signs of something failing in the rears.

Other comments appreciated also.

 

[uHu]

It is at least easy to check the state of your gas springs, aka the nitrogen spheres. Look Here.
If the test gives a lower count, your suspension travel will be shorter.

 

[mainer]

Hey- I had a friend run into this problem. The proportioner valve that seperates the front from the rear had air trapped in it. A gentle tap with a dead blow hammer may dislodge any air pocket that might be residing in it.

 

[haulin79]

Are there two suspension "systems" in the Lexus?
This is what I found http://www.lexus.com/models/lx/470_specifications.html :

1. Accumlators use a fluid to adjust the shocks. Lexus calls this AVS (Adaptive Variable Suspension)

2. The springs are accompanied by air springs which Lexus calls AHC
(Adjustable Height Control).

Do all Lexus LX470's years 2000+ have both AVS and AHC?

Thanks!

 

[uHu]

The two are combined in one system, using oil to transfer the suspension travel to gas springs, through 4 valves (4 for each wheel) regulating the damping effect (shock absorber function) in 12 steps. The ride height is adjusted by pumping more or less oil pressure into the system.
The (1) accumulator just accumulates pressure in order to rise the height faster, AFAIK.
The AVS is also known as "Skyhook TEMS", explained as Toyota Electronic Modulated Suspension, "simulating the car suspended in a Hook from the Sky".
AFAIK all LX470s have it. In Europe the LC100 has always been available with or without.
(When I bought mine, I called dealers all over Europe without finding one w/o the system in stock, so I suffer in comfort with a big smile)