ramangain
Clarksonian disciple
Fresh AHC fluid is clear pink that goes green/brown when dirty and isn't clear. Any other clear color isn't Mr. T AHC fluid AFAIK.
Temp sensor disconnected skips some AHC data (1 Viewer)
- Thread starter MarkTR
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- Thread starter
- #22
I also thought the new fluid I just got from McGeorge would have a pink tint to it-- but I pour out a bit onto the bottom of a glass jar to check and it is about as clear as an oil-based fluid can be.
ramangain
Clarksonian disciple
Dat's moonshine!
I have pasted parts of your Post #17 below then interpolated some responses in blue italics into this text because that is easier for me, then listed a few FSM references at the end. Hope this helps.
@MarkTR: Most important is: The static height and the dynamic ride height can be two different lip-to-hub center dimensions depending upon where the height sensors are mechanically set.
You set the static lip to hub centers equal to make sure both TB's are equally sharing the front load when the truck is level side-to-side. The 19.75" optimum distance is a suggested value that often achieves the correct sharing of the front load between the TB's and the AHC pressure system-but is not set in concrete.
What is important is setting the TBs to where the truck is statically level and that both the TB's and the AHC share the load where the system pressure is in the 6.5 MPa region.
@IndroCruise: Generally, in my comments on IH8MUD, I make the distinction between ‘static heights’ and ‘ride heights’. In part, this is to emphasise for people beginning the AHC journey the importance of getting the Front ‘cross-level’ set correctly before any other adjustments are made, in part this is to distinguish this step using torsion bar adjusters from the subsequent step of adjusting ‘ride height’ with Height Control Sensor adjusters, in part it is because an absolute muddle will result if this sequence is not followed, in part because I try to stay consistent with FSM prescriptions, and in part because I am a bit (a lot?) OCD about these things ....
The point is that at the start (meaning, ‘cross levelling’) the ‘ride heights’, may or may not already be correct. If so, that is well and good. However, it does not matter what the actual hub-to-fender measurements are at the ‘cross-levelling’ stage. It is only important that these measurements be made equal – FSM says within 10 millimetres (0.39 inches), see attachment. It is not part of the ‘cross levelling’ exercise to set the actual heights somehow with the torsion bar adjusters – this actually is impossible given that it is the AHC system, not the torsion bar adjusters, which set the height at which the vehicle will operate – meaning, the ‘ride height’.
So it is not correct to say that “The 19.75" optimum distance is a suggested value that often achieves the correct sharing of the front load between the TB's and the AHC pressure system”. The idea of ‘cross-levelling’ is to equalise the hub-to-fender distances at any height.
Having ‘cross-levelled’ the vehicle, then the ‘ride heights’ can be set using the Height Control Sensor adjusters. At this point, the usual aim is for a stock vehicle (meaning no ‘lift’) to be set at Front: 19.75 inches and Rear 20.50 inches at "N" height setting – or such other heights as the Owner may desire at "N" height setting. Note: these numbers are not FSM numbers but are the widely used IH8MUD approximations of the fiddly FSM specifications for ‘correct height’ at "N" height setting -- see pic below.
Having ‘cross-levelled’ (with torsion bar adjusters) and after that, having set the ‘ride height’ (with Height Control Sensor adjusters), then and only then, it is time to check and adjust the Front and Rear AHC pressures to the Owner’s desired point in the FSM-specified range. At the Front, this involves turning the torsion bar adjusters – clockwise to increase torsion bar load and reduce AHC load and thereby reduce AHC pressures.
@MarkTR: A few bullets made me think if my logic is still fuzzy. I thought when the TBs are cranked/twisted up (CW-increasing pre-load)
@IndroCruise: You have it sort of right. But because there is an ongoing reference to “lengthening the static lip to hub center distance” in the same sentence as ‘torsion bar adjusters’, some confusion creeps in. Strike out those words and your paragraph makes perfect sense. The outcome is that the torsion bar load will increase, the AHC pressure will reduce, but the AHC system will see to it that the hub-to-fender distance does not change.
There are some other points worth making, returning to this quote in your Post #17:
@MarkTR: "As you have noted, increasing hub-to-fender height means that less vehicle weight is carried by less-deflected springs and torsion bars (F = kX, so less X means less F) and correspondingly more vehicle weight is carried by the AHC system. In turn, this means higher Front and Rear AHC pressures,"
@IndroCruise: The statement is correct but I may have placed it in a position that has caused confusion – if so, apologies are offered.
All this statement attempts to do is highlight that if height is increased (for example, using Height Control Sensor adjusters), then springs and torsion bars are extended or unwound and carry less weight, with the consequence that the AHC system must carry more weight and AHC pressures will increase.
As an illustration, some Owners choose to do a ‘sensor lift’, or, may have individual ideas on the Rear-to-Front ‘rake’ they prefer. This involves moving the Height Control Sensors upwards in the slide adjusters (and/or shortening the heim bolt at the Front).
The effect is that the zero (or near zero) point seen on Techstream at “N” height now occurs at a greater hub-to-fender distance. It also means that less weight is carried by springs/torsion bars, more is carried on the AHC system, and AHC pressures rise. For the health of the AHC system, this rise in AHC pressures should be countered by torsion bar adjustment at the Front and spacers or upgraded springs at the Rear.
One simple way to get an idea of size of these effects is to raise the vehicle to “HI”, then observe the Techstream readings and also measure the hub-to-fender distances at this setting.
@MarkTR: And this
"No point in adjusting anything until front ‘cross-level’ has been done; no point in adjusting AHC pressures until ‘ride height’ is where you want it; no point in checking overall ‘globe’ condition via “HI” and “LO” fluid level differences at AHC tank until AHC pressures are in the correct range..."
To decide if you like the Ride Height I assume that you measure the lip-to-hub center after you have cycled from L-N a few times and the truck is running so the AHC is operating. If you like the height where the sensors have raised the truck- you are good to go.
@IndroCruise: Yes. And you also need to ‘like’ the AHC pressures at this point, because these need to remain in the FSM-specified ranges (generally preferred in the lower half of the range) for good damping performance and best ride comfort.
@MarkTR: What if the Ride Height is not level L to R (but the static was)- do you start playing with the TBs to get things level and the pressures where you want them while the truck is running-or is this a case where you play with the sensors to get the Ride height level?
@IndroCruise: Yes. There usually is some iteration and ‘fine tuning’ when setting up the suspension on an AHC-equipped vehicle. For example, using torsion bar adjusters to correct Front AHC pressures may not have been done exactly equally on both sides. As a result, there may have been some loss of ‘cross level’ – easily fixed by following the attached ‘cross levelling’ procedure. Sometimes this only requires a minor tweak of one or other torsion bar adjuster.
@IndroCruise: No. The Height Control Sensor adjusters play no role in ‘cross levelling’ the vehicle. The LC100/LX470 AHC system is a two-channel, Front-and-Rear system. It does not and cannot raise or lower each of the four wheels individually.
In addition, when the vehicle is stationary or in motion with the wheels straight ahead, then the Front Gate Valve in the Control Valve Assembly is open.
This means that the Left and Right sides of the Front AHC system are hydraulically connected and are at the same pressure (and carrying equal load), whatever that pressure may be.
Moving one Sensor up or down to a different relative position to the other Sensor will cause the different voltage signals to be sent by each Sensor to the AHC Electronic Control Unit. (This also will show as a not-near-zero value in inches (or millimetres) on the Techstream readout).
What does the ECU do with the conflicting inputs?
The ECU appears to average the Front Left and Front Right signals from the respective Height Control Sensors – this makes sense, although I have not seen that documented.
Whatever signal is accepted, the ECU will cause operation of the AHC pump and/or the Front Levelling Valve in the Control Valve Assembly. In turn, the Front of the vehicle (not just one side) will raise or lower until the ECU receives the signal which best matches the selected height (“LO”, “N” or “HI”).
If there is very wide difference in signals due to inappropriate Sensor adjustments or Sensor faults (the FSM is less than clear on what is ‘very wide’), then the ECU will place the AHC and TEMS systems in ‘fail safe’ mode. In this mode, the ECU prohibits AHC operation and prohibits adaptive damping by TEMS until the cause(s) of the conflicting signals are resolved. There may or may not be a DTC when this happens but the effect and the symptoms will be obvious.
Getting out of this muddle can be a very unhappy experience. It is another reason why it is a good idea to stay with the recommended sequence of steps in AHC adjustment in the first place.
The Rear AHC system is a little easier. It has its own Gate Valve and Levelling Valve in the Control Valve Assembly but there is only one Height Control Sensor. However, if there are wide differences in Sensor signals between the Rear Sensor and the Front Sensors, then erratic effects will be experienced.
Here are a few more good references which may be worth a browse if you have not seen them before. The AHC/TEMS General Description listed below is especially recommended -- it describes the location and function of the various AHC/TEMS components with useful diagrams.
I see from your posts after Post #17 that you have had great successs and are on top of things already. Maybe this post will fill in some grey areas or maybe it will be of some use to you or others in the future. Go well!!
An IH8MUD reference:
The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/
Factory Service Manual (FSM) references relevant to AHC/TEMS:
The AHC/TEMS General Description by Toyota/Lexus with good diagrams setting out how the AHC and TEMS systems are supposed to work is found in the Factory Service Manual (FSM). It is an informative and easy read:
Go to: https://lc100e.github.io/manual/
(This is a Toyota LC100 manual but under the skin where most things are the same, especially for AHC/TEMS, it does just as well for LX470):
At the tabs at the top on the left hand side of the opening page at the above link, go to:
New Car Features > CHASSIS > Suspension > Active Height Control and Skyhook TEMS
Eventually you will need to know something about AHC specifications, settings and and inspections:
Go to: https://lc100e.github.io/manual/
At the tabs on the left hand side of the opening page go to:
Repair Manual > SUSPENSION AND AXLE > ACTIVE HEIGHT CONTROL SYSTEM (Independent Front Suspension)
then look at the tabs for BLEEDING, ON-VEHICLE INSPECTION, LOCATION, ADJUSTMENT
As you become more familiar with the vehicle, the section on AHC/TEMS Diagnostics reveals many deep secrets!
Go to: https://lc100e.github.io/manual/
At the tabs on the left hand side of the opening page go to:
Repair Manual > DIAGNOSTICS > ACTIVE HEIGHT CONTROL & SKYHOOK TEMS
AHC Layout:
AHC Standard Height Specification at "N" height setting per Factory Service Manual:
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- Thread starter
- #25
Thank you again- I am beginning to get a clearer feel for how the system works. Even though my last data set looks good, I feel I have not nailed my setup just yet since I am not positive that my TB's are equally sharing the load.
As far as lessons learned--I now realized that I put way too much importance on trying to get both sides up to 19.5" and not realizing that once I started to cycle from L-N that my carefully measured heights would now be dictated by the height sensors. I went off-script at this point and I got wrapped around cranking up the TB to get to 19.75" each time I cycled. My brain was in the fog of war and I could not understand why my 9.75" kept going down after each cycle. Of course, this kept lowering the AHC pressures. While this sort of registered- I did not make the connection.
Now I know that my left side sensor height is set at 19.25" and my right side sensor is set at 19.5" and that is where my measurements will go after each L-N cycle.
When you and others got to the heart of the matter after seeing my data, I made the connection. I knew I had to crank down the TB's to raise the pressure- but after having done so many cycles of going from L-N and attempting to get the front end back up to 19.75 and cranking on the TBs, I lost count of all the turns I made on both TB's.
I know that I had to do many turns on the driver's side TB to bring the left side up to within the 19.5-19.75 height. On my first cheat sheet, I had to crank up the left TB 7 full turns. This made sense due to age and mile. But after many L-N cycles I lost my TB turn count.
But I had leveled the front and it was still pretty level, so I backed down the TBs equally until the pressure when up to 6.6 and I had L/R -0.2" sensor height reading. But because the 6.6 MPa is the average of the L and R, I now have no idea if my left TB is contributing more of the force to lift the front end up than the right TB.
To get this answered I feel I really should go through the cross-level process again and be sure that both TBs are sharing the load equally.
Does the matching -0.2 on both front height sensors provide a clue about how the TB's are sharing the load?
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ramangain
Clarksonian disciple
Now you're looking at branches and losing sight of the forest and the trees.
uHu
Bridgeburner
Re. fluid looking clear:
If you by "pulled out fluid" mean that you took some out of the reservoir, it doesn't say anything about the condition of the fluid at the globes/valves/shocks. As this is a "linear" system, there is no circulation of the fluid. It actually takes years for some of the fluid from the top to reach the globes, and v/v. You have to crack a bleeder to check the fluid.
Otherwise, it looks like your ahc system is well taken care of. We are fortunate (or spoiled?) to have indrocruise with us.
Hang in there! You are tracking well through the “learning curve” with some learn-by-doing experience and frustrations – but this is the best way. We all had to pass through this learning experience.
From my previous Post, you now know that the when the vehicle as at rest while you are doing adjustments, Front Left AHC and Front Right AHC are hydraulically connected. (You can read about this when you get time to read the “General Description” document at the link provided previously).
The hydraulic connection means that that the Front Left and Front Right parts of the AHC system are at equal hydraulic pressure when the vehicle is stationary (also when the vehicle is being driven straight ahead).
In this condition, whatever the Front AHC pressure may be, it is the same at the Front Left and Front Right parts of the AHC system.
This is the pressure in the Front Shock Absorbers and it is equal on both sides. On an AHC vehicle, the Shock Absorbers are not like conventional shock absorbers – they are simple hydraulic struts which support part of the vehicle weight and are used to vary the height of the vehicle.
This means that Front Left and Front Right parts of the hydraulic system are carrying equal shares of the vehicle load, whatever the Front AHC pressure may be.
You already knew that the front torsion bars are just springs by another name.
You also already knew that the deflection of a spring (or a torsion bar) is proportional to the weight it is carrying – twice weight causes twice the deflection in a perfect spring.
Unless there has been some damage to the torsion bars, we assume that the Left and Right torsion bars have identical ‘spring rates’ – meaning, the same pounds of weight on both sides will cause the same inches of deflection on both sides.
We assume that the weight of the vehicle eventually transmitted to the ground is the same on both sides. (This assumption may not be perfect but it is good enough provided that any additions to the vehicle are evenly distributed, or if the added weight is unevenly distributed some allowance will need to be made. Assume that weight distribution is equal on both sides for now).
Given that the share of the vehicle weight carried by the AHC system is the same on both sides, and if the torsion bars on both sides have identical spring rates, then any difference in deflection on both sides will be due only to the torsion bar adjustment (because the weight carried by the AHC system on both sides is equal).
If the Front Left and Front Right hub-to-fender heights are the same, then the Front Left and Front Right torsion bars are carrying equal weight.
This is why so-called ‘cross-levelling’ is done first in the AHC review or adjustment steps -- to get the Front Left and Front Right hub-to-fender distances the same (within the FSM tolerance), measured with a tape-measure, (nothing whatsoever to do with the Height Control Sensors or Techstream), and because then the weight carried by each torsion bar is the same (unless the vehicle weight is unevenly distributed).
Suggestion:
- Start again at the beginning – follow the steps on the Cheat Sheet, to which the following words are added for additional clarity,
- Put Techstream to one side and leave it there until later steps – its premature use is the cause of your frustration. It has taken you into exactly the muddle you wished to avoid,
- Cross-level with torsion bar adjusters and only a tape-measure (not Techsteam nor Sensor readings) and a wrench with engine and AHC “OFF” – the aim is to achieve equal Front Right and Front Left hub-to-fender distances. It does not matter what the actual measurements are – just make them as equal as possible, so that there is no unacceptable ‘lean’ and so that you know that the torsion bars are equally loaded. The number of adjuster turns on either side is irrelevant (provided you don’t run out of adjustment). All that matters is equalising hub-to-fender distances. You have no interest in AHC pressures at this stage,
- Adjust ‘ride heights’ if necessary, using a tape-measure and small wrenches with engine and AHC “ON” by moving the Height Control Sensor adjusters, to achieve the ‘ride heights’ you want – same Left and Right but different Front and Rear (IHMUD recommendation: Front: 19.75 inches; Rear: 20.50 inches). Ask questions about this procedure and the next step if you need more detail. This step and the next step can be a fiddly process. If the current ‘ride heights’ are OK, then leave them alone,
- When the ‘ride heights’ are where you want them, then with engine “OFF” (do not want AHC Pump working for this step) but with ONLY ignition “ON” and with Techstream connected so that you can view the Height Control Sensor readings, use the Height Control Sensor adjusters to move each Sensor until it reads as close as possible to zero inches on Techstream,
- Now – and only now, not before the above steps have been completed, AHC pressures should be measured. With engine “ON”, move from “N” height to “LO” height and then back to “N” height, wait say 60 seconds to be really sure that the AHC Pump has completed, and that Height Control Accumulator has recharged and the suspension has settled at “N” height, then measure and record the AHC pressures with screenshots,
- If necessary, adjust AHC pressures using Front torsion bar adjusters, consider spacers and springs at the Rear,
- When all the above steps are done, conduct the ‘globe’ condition test by observing fluid levels at AHC Tank at “HI” and “LO”. It is meaningless to do this test without setting desired heights and correct AHC pressures.
No -- the height sensors cannot tell you anything about the torsion bar loadings. A tape-measure is the way forward as mentioned above. And just to repeat, the Height Control Sensor adjusters cannot be used to cross-level and are incapable of adjusting different heights at individual wheels.
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- Thread starter
- #30
Thank you again. The more you explain -the clearer I am about how the system works. I am going to flush the system next and then I will repeat the Cheat Sheet steps. I am only a 1/4" off of being statically level side to side so I think I am very close based upon my static measurements and the system pressures reported on the last datasheet.
Much better than when I got the truck- so progress.
When I look at your data sheet at your Post #18, I am reminded that:
Front AHC Pressure: 6.6 Mpa actual versus FSM range 6.4 MPa to 7.4 Mpa
Rear AHC Pressure : 7.0 Mpa actual versus FSM range 5.6 Mpa to 6.7 Mpa (single fuel tank) or versus 5.9 Mpa to 7.0 Mpa (with optional sub-tank)
Front AHC maybe could be a touch higher – but not worth worrying about.
Rear AHC maybe could be a touch lower – but suggest just watch this by testing every 12 months, add spacers if concerned or if Rear AHC Pressure deteriorates, or consider replacement springs -- but not urgent.
Height Control Sensor readings: all good, all close enough to zero.
At your Post #20, you report:
- Height Accumulator Pressure: 10.5 Mpa – no FSM prescription for this but 10.5 Mpa is normal,
- Clean relatively young truck (2005 LX470),
- Minimal rust,
- Service records available,
- Some maintenance actions required, appear minor
Front is cross-level within 0.25 inch (versus FSM tolerance of within 10 millimetres or 0.39 inches difference side to side) – tape-measured 0.25 inch actual difference is not worth worrying about.
Conclusion:
So it looks like your truck already is in very good shape, nothing to worry about beyond keeping routine maintenance and repairs up to date, including ongoing periodic checks of AHC pressures, and, periodic AHC Fluid changes which Owner’s Manual suggests be done very 5 years or 60,000 miles (Personal view: do AHC Fluid change twice as often – every 2.5 years or 30,000 miles -- not difficult, not expensive and good insurance).
ramangain
Clarksonian disciple
I'll summarize for @IndroCruise - send it
- Thread starter
- #33
IndroCruise, ramangain-- I agree- I will stop getting into the weeds and go on to other issues that I need to take care of to baseline my new truck.
Love this truck and love this forum- what a great group!!
Love this truck and love this forum- what a great group!!
ramangain
Clarksonian disciple
AHC is good stuff to study on the throne, IMHO
@ramangain has worked out where I get my inspiration!!
By the way @MarkTR, the previously referenced "General Description" document IS a good read -- at your choice of venue
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