Bouncy AHC. Can I check health of system before trying replacing globes? (3 Viewers)

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I got a new 2004 LX470 and it came with a bouncy rear end. I know the accumulators need replacing.
I want to keep the AHC system (I like the ride) if I can and want to know if there's a way to check/inspect the rest of the system for issues before I decide if I want to replace the rear globes or ditch the whole system.
What are some other AHC wear items that I should be looking at replacing?
 
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Thanks for this, but can I run some of these diagnostics with faulty globes? I'm guessing not.
 
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I’m waiting on the cable to arrive...
In the meantime, this doesn’t look good. The previous owner probably added extra fluid to try abs fix the issue.

5E0936DE-DB0D-463B-B0DB-DEC828F96D1D.jpeg
 

suprarx7nut

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Here's the thing about AHC: Almost all the components last the lifetime of the vehicle, with a few exceptions and one disqualifier.

The exceptions are the globes (gas chambers), the sensors and the disqualifier is rust.

1. The globes have a known limited lifespan. Around a decade or 150k miles.
2. The sensors can be checked with techstream or just watching for flashing AHC lights. Smooth height values = good sensors.
3. Rust can be visually checked. The number of people I've seen with failed lines with non-rusted rigs are easy to count. Because the number is zero. No rust = no problem. I see some rust on the bolts in your picture. Check the lines for AHC. If they're rusted badly, you might consider replacement. Replacement isn't terribly expensive, but it is labor-intensive. Those lines were not designed for easy replacement. Instead they were routed for an incredibly low risk of physical damage, n which the engineers succeeded. I don't think I've seen anyone break an AHC line, even in extreme off-roading.


I would proceed with confidence on the globes. There is an ENORMOUS market for globes. If you replace the globes and then ditch the system due to rust a year from now, I bet you'd get most your money back in the used market for the globes.
 
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That's really helpful. Thank you. There's definitely rust, but there aren't any visible leaks that I can see so maybe it's not an issue yet.
Another thing of note: the car doesn't stay in high mode for long. It tries to rise up but the H light keeps flashing and it eventually comes back to normal height.
 

flintknapper

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That's really helpful. Thank you. There's definitely rust, but there aren't any visible leaks that I can see so maybe it's not an issue yet.
Another thing of note: the car doesn't stay in high mode for long. It tries to rise up but the H light keeps flashing and it eventually comes back to normal height.

When at speed or when parked? If 'at speed' it is only designed to hold 'high' under certain parameters.

AHC modes.png
 
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Another thing of note: the car doesn't stay in high mode for long. It tries to rise up but the H light keeps flashing and it eventually comes back to normal height.
In addition to the conditions posted by @flintknapper, also consider loads and hub-to-fender heights (Standard: Front 19.75 inches; Rear 20.50 inches -- measured with a tape measure).
More load = more AHC pressure,
More height = more AHC pressure,
Tired rear springs (replace) plus tired torsion bars (adjust) = more AHC pressure.

When AHC pressures are excessive, the system will refuse to raise and/or will sink. This is about the excessive load share carried by the AHC system and a requirement to transfer more load to the torsion bars and springs to get AHC pressures back into the correct range -- it is not about 'globe' condition. The FSM provides the following guidance on load limits at correct heights and correct AHC pressures:

AHC Limits.jpg


Thinking about 'globes' -- Ideally you could check overall condition of the four 'globes' using the HI/LO Test -- recording the difference in graduations at the AHC Tank at "HI" and "LO" heights (14 graduations = as new; 7 graduations = replace 'globes' per FSM at correct AHC pressures -- BUT this test only works when the vehicle can be raised from "LO" to "HI". The outcome is only comparable with FSM recommendations when AHC pressures are correct.

It is vitally important to measure AHC pressures as part of the maintenance and monitoring of the system -- but be aware that AHC pressures alone tell nothing about the condition of the 'globes'.

Poor 'globe' condition certainly will result in poor ride quality.

In addition to advice in earlier replies and if not already seen, suggest have a look at the General Description of the AHC and TEMS systems at
https://lc100e.github.io/manual/
Go to tabs at Index Panel, top left of opening page -- New Car Features (first item in the list) > CHASSIS > Suspension > Active Height Control Suspension & Skyhook TEMS.

Then go through "The ABC's of AHC" thread assembled by @LndXrsr mentioned at Post #2 above,
and,
view the video and "Cheat Sheet" provided by @suprarx7nut at
AHC Basics for dummies Video re CrossLeveling, Height Sensor adjustment, TB tweaking - https://forum.ih8mud.com/threads/ahc-basics-for-dummies-video-re-crossleveling-height-sensor-adjustment-tb-tweaking.1225842/#post-13383401

DEFINITELY follow through on the diagnostic procedures using Techstream when your cable arrives. This can take a bit of effort to set up but good guidance can be found here:
This thread is lengthy but the early posts provide most of the required information.

Then suggest post a screenshot of your Techstream test data when you get to that point for more feedback.

The unknown blue fluid should be flushed out of the system as best possible as soon as possible and replaced with genuine (pink) Toyota/Lexus AHC Fluid. Wrong fluid may have caused unknown internal degradation, damage and formation of sludge, all impeding fluid flow within the system -- or you may be lucky!

Next after 'globes' (which are a wear item as mentioned by @suprarx7nut) come the under-recognised problems caused by inadequately maintained and degraded Height Control Sensors.
 
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There’s no load in the car currently. The globes are suspect because the rear end bounces a lot when going over bumps.
I’ll definitely run a diagnostic once I have TS setup.
 
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There’s no load in the car currently. The globes are suspect because the rear end bounces a lot when going over bumps.
I’ll definitely run a diagnostic once I have TS setup.
Apologies offered for my poor choice of words -- by "load" I meant "overall weight of vehicle and contents" and how that is shared between the AHC hydraulic system and the mechanical system of springs/torsion bars. These "shares" do not change with the declining condition of the 'globes'. Techstream will not reveal the condition of 'globes' but certainly will reveal the AHC pressures (among other things) which will help identify the reasons why the vehicle will not raise. If never replaced by previous Owners, it is highly likely that the 'globes' in a 17 year old vehicle are due for replacement, due to inevitable nitrogen leakage over the years. The loss of nitrogen from 'globes' probably is the most common cause (but not the only cause) of poor damping and bouncy ride. Tired rear springs needing replacement and tired torsion bars needing adjustment also are almost inevitable in a 17 year old vehicle. These cause excessive AHC pressures which in turn also cause poor damping and a bouncy ride. Conflicting signals from degraded or out-of-adjustment Height Control Sensors may lock the variable damping at Step 8 of 16 Steps (so-called 'fail safe mode') and give a bouncy ride, especially at town speeds. All of this is fixable -- and usually much, much cheaper than a replacement non-AHC suspension -- unless there is cost-prohibitive rust.
 
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When parked
I lied. I tried this again just now and the car raises and lowers correctly and stays in mode. I think last couple of times I checked I was sitting in traffic and had the car in D. It probably needs to be in Park to function correctly.
 

suprarx7nut

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I lied. I tried this again just now and the car raises and lowers correctly and stays in mode. I think last couple of times I checked I was sitting in traffic and had the car in D. It probably needs to be in Park to function correctly.
It should function in P or D, but it may not move while the foot brake is applied. The suspension and drivetrain have to load/unload together or you get some binding in a variety of places.

AHC needs doors closed and foot off the brake (and a low moving speed).
 
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I got TS connected. Starting by taking out the excess fluid
26F36FB5-EF52-4D2F-B1D9-4A29986CE133.jpeg


This much came out before hitting the max line. There’s some weird pink stuff settling at the bottom. Signs of moisture?

AE646CE2-BAD7-41DF-B9FC-BEB869DB6E63.jpeg


BE04BB48-0208-4848-BA5B-5EE1FD64A803.jpeg
 
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OK...going through the diagnostic process I realize I didn't need to remove the access fluid.
 
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I followed this video:

Here are the numbers:


Neutral height - Fender to center of wheel
FL: 19.5
FR: 19
RR: 19.9
RL: 20.2


Pressure test in Neutral
Attempt 1

Front: 8.6
Rear: 7.7

Attempt 2
Front: 8.8
Rear: 7.4

Attempt 3:
Front: 8.4
Rear: 7.7

Height control sensors at N: 0.0 (for all)

Gradation check between H and L: 8 (I didn't add the fluid back)


I didn't adjust the torsion bars but the high front pressure indicates I need to do that. The heights in the front are pretty even though. What should it ideally be, after adjusting the torsion bars?

The rear pressure is also high, and the gradation check seems things are within spec. So that leads me to believe the globes are fine but I need new springs in the back? That's what creating the crazy bounce? One more thing, both the swaybar end links in the rear are broken 😅 Dunno if that's contributing to the bounce.
 
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I tried this again just now and the car raises and lowers correctly and stays in mode
Now that "LO"/"N"/"HI" height selection function is sorted, you may wish to run the on-vehicle test for overall 'globe' condition, as attached.

This will give you some idea but won't be the Real Deal until
  • "N" height is correctly adjusted, and,
  • AHC pressures are measured and adjusted into the correct range using Techstream, and,
  • the vehicle is in the specified weight condition.
The test does not reveal the condition of individual 'globes'.

As the 'globes' deteriorate or 'wear out' (meaning nitrogen pressure is lost slowly from the gas side of the membrane in the 'globes' into the fluid), then there is progressively less and less gas pressure to push the fluid in the fluid side of the membrane back to the AHC Tank as the vehicle settles to "LO". Over the years, this shows up as a progressively declining difference in 'graduations' on the side of the AHC Tank when this test is done.

Obviously, for comparison purposes of just one variable (namely, overall 'globe' condition), this test needs to be done with other variables held constant or at least similar each time the test is done, specifically, at same or similar measured AHC hydraulic pressures, and, at same vehicle weight.

For this reason the FSM states that the test be done with AHC pressures in the FSM-specified range with the vehicle in the FSM-specified weight condition -- variable loads removed and with fuel tank(s) full.

Sometimes a misconception is seen in IH8MUD posts that poor (meaning high) 'globe' pressures indicate that the 'globes' are 'worn out'. This is not correct. The AHC pressures come only from that part of the vehicle weight supported by the AHC system and not supported by the springs/torsion bars. If the total weight of the vehicle is unchanged, and the height of the vehicle remains unchanged, then the weight carried by the springs/torsion bars remains unchanged, and the weight carried by the AHC system also remains unchanged. This means the AHC pressures also remain unchanged regardless of 'globe' condition. The pressures would remain unchanged even if the 'globes' were removed and their connections to the Actuators were blanked off completely.

Good that AHC Fluid change is proceeding successfully. The dark colour indicates that the fluid is old, breaking down, and has picked up detritus from worn or degraded components in the system. The mix of colours probably is an emulsion of moisture, probably with some entrained gas from the 'globes', plus whatever else has resulted from the PO mixing the strange blue fluid into the system. It is almost impossible to fully flush the AHC system, so best if several bleeds are done to get as much as possible of that horrible-looking stuff out of there. Better fluid often results in better AHC system performance and sometimes a better ride is reported. Periodic fluid changes -- at least those specified in the FSM but more frequently is better -- for best performance and longevity of the system.

Hope all goes well! Maybe you could post a screenshot of Techstream results when you get to that point?
 

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Yeah I'll have to perform the globes test again once the front and rear pressures are under spec. But from the test I just did, the gradation level is definitely greater than 7.
 
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Just adding another detail: The bounce in the back is a harsh bounce, not a spongy bounce.
 

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