AHC/AVS Function Check

[Tinkerer]

Does anyone know of ways to verify the function of the AVS system on LX470? I am suspecting that my AVS damping may be starting to stiffen - not as good at absorbing sharp bumps. But my senses could be wrong...it is subtle... I'm not talking about height control and leveling. I'm refering to the damping & spring rate control functions. Have read that a sign of failed nitrogen spheres is stiff/hard reaction to bumps. Comments appreciated.

 

[Drinkin40s]

I don't know how many miles you have on your AHC fluid, but that might be the culprit.

 

[uHu]

You can start by this easy test for the condition of the nitrogen spheres (gas springs), which has the following conditions (at least):
1 - The vehicle height is correct in L, N and H.
2 - Any air in the AHC fluid has been bled.
(Other factors like spring tension (shock absorber neutral pressure), enough fluid, etc...)

Test:
1 - Adjust height to LO
2 - Record fluid level in the AHC fluid reservoir (graduations at front corner)
3 - Adjust height from LO to HI
4 - Note the difference in fluid level

The change should be 7 graduations or more. (8 or more for OZ !!?)


Your symptom sounds like what I had when the gas springs started to fail.

 

[Jim_Chow]

Assuming you get 7 gradations or more, I'd flush the fluid. I had mine flushed at 51K mi, figuring the heat here in AZ takes its toll on fluids. I suspect the fluid is like brake fluid in that it probably absorbs moisture, so if you live somewhere humid, it could become an issue.

 

[Tinkerer]

You can start by this easy test for the condition of the nitrogen spheres (gas springs), which has the following conditions (at least):
1 - The vehicle height is correct in L, N and H.
2 - Any air in the AHC fluid has been bled.
(Other factors like spring tension (shock absorber neutral pressure), enough fluid, etc...)

Test:
1 - Adjust height to LO
2 - Record fluid level in the AHC fluid reservoir (graduations at front corner)
3 - Adjust height from LO to HI
4 - Note the difference in fluid level

The change should be 7 graduations or more. (8 or more for OZ !!?)


Your symptom sounds like what I had when the gas springs started to fail.

Thanks uHu. I seem to remember reading this procedure in the FSM, but I don't have my FSM at the moment.

I changed the AHC fluid a few thousand miles ago, with plenty of bleeding to ensure removal of air & old fluid. (I suppose that if the nitrogen spheres were failing, what appeared to be air bubbles could have actually been nitrogen bubbles...

My LX just turned over 100k miles. How many miles were on yours, when you diagnosed failing spheres? Also, did you find only one, or more than one failed?

 

[uHu]

My problem was brake fluid in the AHC system, following advice from two toyota service managers. Killed all four spheres at around 60 k km.

And about air or nitrogen: Air consists of 78 % nitrogen.... But of course the interesting ? is: where did the bubbles come from?

Did you read your graduations yet? (takes three minutes)

 

[Tinkerer]

My problem was brake fluid in the AHC system, following advice from two toyota service managers. Killed all four spheres at around 60 k km.

And about air or nitrogen: Air consists of 78 % nitrogen.... But of course the interesting ? is: where did the bubbles come from?

Did you read your graduations yet? (takes three minutes)

Actually, I would guess that if bubbles are observed in fluid discharging from bleed valve during bleeding, it could mean:

- Air entrapment, due to air absorbed into fluid in vented reservoir, then very gradually passing into pressurized system fluid as fluid is pumped into system and released back into reservoir repeatedly, during normal system height adjustments e.g. to compensate for loads etc. Over several years of use, this could allow a significant amount of air to be absorbed by the fluid and passed into the pressurized system.

- Air could also be absorbed into fluid at the "shocks" (dampers) at each wheel, at the piston shaft-to-seal interface, despite pressurized condition of fluid at that region (due to chemical diffusion principle).

- As noted, nitrogen might diffuse from the spheres into the fluid, especially if they fail. Since it is nearly impossible to hermetically seal a liquid-gas interface like this (with either a wiping seal or a flexible membrane), nitrogen probably diffuses into the fluid at a very slow rate in any case, even when the spheres are new and in good condition.

- There might be residual air from the factory fluid evac & fill (or fill & bleed) operation. Based on what I observed in doing 2 separate fluid bleed jobs and vehicle operation between the 2, I think the system will perform adequately even with a small amount of residual air in the system, so Toyota probably specs a tolerance allowing a small amount of residual air, in the factory fill process.

I checked, and my LO-HI fluid level changes by 12 graduations. I didn't check heights, pressures, etc. first though, so who knows what that means? Other comments welcome (including any challenges to my ideas above).

 

[Wilsil]

Reviving an old topic (2006!!)
I tried to see the AHC fluid level in the reservoir, but I can't.
It is clear fluid and the bottom half of the reservoir looks darkish.
When I go from Low to High, I can't see any movement.
How do I check the graduations if I can't see the level?

 

[Wilsil]

Found a way!!
An electrical wire with insulation.
I dipped it in the reservoir through the filler point and took the markings which I held against the graduations at the reservoir.
It is a total of 8 between Low and high.