AHC Longevity Question

Joined
Feb 9, 2009
Messages
22
I had just a quick question to see if my situation was normal.

I have a 2002 LX470 with 250,000 miles.
The only AHC maintenance has been periodic flushing and a TB adjustment.

Original globes with 7 graduations between LOW and HIGH.
Front pressure reads 6.9 Mpa-g
Rear pressure reads 6.7 Mpa-g
FL/FR Height Sensors are at 0
Front R/L hub center to fender both measure 19.5”
Rear R/L hub center to fender both measure 12.5” Sorry, 20.5"

Has anyone else experienced zero AHC maintenance with 250K miles or am I the lucky one?
 
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BullElk

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Jun 19, 2013
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Mobile, AL
My 2000 LX has 350k miles and never had an issue with AHC. I may have changed the fluid once but not more than that. Do not know the graduation test results
 
Joined
Feb 9, 2009
Messages
22
I have 375k and just about the same maintenance as you, really like the system

Love it, I was a little afraid of the AHC prior to buying my LX almost 12 years ago. Best vehicle I've ever owned, and I've owned a bunch!
 

ramangain

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Feb 6, 2020
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Oh High Oh
I had just a quick question to see if my situation was normal.

I have a 2002 LX470 with 250,000 miles.
The only AHC maintenance has been periodic flushing and a TB adjustment.

Original globes with 7 graduations between LOW and HIGH.
Front pressure reads 6.9 Mpa-g
Rear pressure reads 6.7 Mpa-g
FL/FR Height Sensors are at 0
Front R/L hub center to fender both measure 19.5”
Rear R/L hub center to fender both measure 12.5” Sorry, 20.5"

Has anyone else experienced zero AHC maintenance with 250K miles or am I the lucky one?
If you are a fear mongerer, you'll be replacing globes soon
 
Joined
Dec 6, 2016
Messages
503
Location
Brisbane, Australia
Sorry, I meant to say 20.5", which is factory dimensions from what I understand.

Original post edited to reflect the correct measurement.

Impressive numbers which attest to great AHC longevity with good maintenance!!

By FSM and many at IH8MUD including me, "HI/LO Test" at 7 graduations at AHC tank means that 'globes' are past their best, much nitrogen has diffused from 'globes', damping is degrading and causing ride quality to diminish. Judgement about acceptable ride quality is a personal thing but there will come a time to replace all four 'globes' .... for me that was at 8 graduations but that was a conservative decision before some very long trips (thousands of rough kilometres).

Just to be clear, good AHC pressures at such a big mileage certainly indicates that attentive maintenance has occurred including periodic replacement of AHC fluid (which does deteriorate with time) but tells nothing about 'globe' condition. The AHC pressure readings relate to the hydraulic pressures and the share of load between the AHC system and the torsion bars and springs -- these hydraulic pressures change with load share but are unchanged by 'globe' condition (nitrogen loss). The slow but inevitable loss of nitrogen over time is detected by the reducing change in levels at the AHC tank during the periodic "HI/LO Test" and is caused by the reduced displacement of AHC fluid when there is less and less nitrogen pressure to push AHC fluid back to the tank when the suspension is moved between HI and LO.

The actual FSM Height Specification measurements at "N" height are attached for interest. They are finicky to measure and have led to the more practical approximation by IH8MUD Members of the hub-to-fender measurements of Front 19.75 inches and Rear 20.5 inches (or 500 millimetres and 520 millimetres respectively). These 'measures' are now widely used to good effect but we cannot say that they come from the FSM -- because they don't.

Use of the approximation is supported by Height Control Sensor Measurements of close to zero being achieved.
 

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