Hi Azi,
You seem to have made good progress since I last replied to you with the summary and attachments
here.
Maybe you can guess, I am stuck indoors due to COVID-19 warnings. I must apologise for having too much time and for writing long posts in too much detail.
Due to some misunderstandings there will be some rework to do. Don’t worry about that. We all have had to learn-by-doing and benefitted from reading other experiences on IH8MUD. I admire your efforts to give more life to a LC100 with AHC and which is 20 years old and travelled 400,00 kilometres.
It is not hard to correct things from where you are now – but it is vital that the suspension adjustments be carried out in the
correct sequence, without any jumping to conclusions from premature Techstream measurements of pressures, and without skipping any steps and without getting the steps out of order.
Firstly, please ALWAYS start with the height readings, preferably hub-to-fender using a tape. Just take the readings, no adjustments until later as discussed below. Be sure that the vehicle is on a level surface, no driver, no passengers, no luggage or other contents, both fuel tanks full, steering straight ahead. The hub-to-fender height numbers are measured with the engine “OFF” and AHC “.OFF”.
Again, please DO NOT start by worrying too much about premature Techstream pressure readings – that just causes confusion.
Neutral pressure readings ONLY make sense when the heights are correct. If the vehicle is high, then the pressures will be high because the AHC system is carrying too much of the weight of the vehicle. If the heights are not correct then the pressure readings cannot be compared with the FSM specifications for Neutral Pressures and will not make sense to other IH8MUD Members when you ask questions.
Techstream and pressures are important later but please forget them for a few minutes until you have read the rest of this post.
As slus mentions in post #6, heights can be measured in different ways but if you use the hub-to-fender method you can compare with other IH8MUD Members and they can understand your measurements.
Also be aware that the pressure readings obtained using Techstream, or direct hydraulic readings, tell you NOTHING about the condition of the ‘globes’ (also called spheres). The ‘globes’ will be discussed later in this post.
The “HI/LO” test indicates the condition of the ‘globes’ (spheres) – as you mention, 14 graduations at AHC tank when ‘globes’ are new, 7 graduations means end of life of ‘globes’. As indicated in the FSM extract attached to my previous post, this test also only makes sense when heights are correct.
At the moment, your heights are not correct. This means that your Techstream pressure readings are kind of interesting but the readings are not conclusive. It also means that your “HI/LO” test (4 graduations) also is not conclusive.
Your heights also show that Front Left is low and Rear Right is high. At the moment, the vehicle is tilted downwards at the Front Left corner and upwards at the Rear Right corner. This is natural. It is exactly as expected. Remember that the vehicle is rigid. When the Front Left is raised, the Rear Right will be lowered which will mostly correct your situation. To illustrate, think of another rigid object like a book. Hold it in a fixed position at two diagonal corners. Now make one of the free corners move up. Observe that the remaining corner will move down. This is what you will see with your vehicle.
Your question was:
“Does the front side to side height correction will help to the rear, cause I have an obvious difference at the back - driver's side sag?”
The answer is
“YES – but driver’s side sag is not the problem” -- for the reasons given above and explained further below. After other things are corrected as described below, then it will be the right time to look again at rear hub-to-fender heights.
Toyota have assumed that the vehicle will remain in the same condition as manufactured. Provided that assumption remains true – no twists in the chassis – then if the two front corners are at the correct height after being correctly cross-levelled at the front, then only one height sensor is necessary at the rear and the rear heights will be the same on both sides -- provided the chassis is perfect. In the real world things are never perfect. Small differences and tolerances can arise. These are usually too small to worry about. If they are large, it is important to find the cause.
In your case, please first cross-level the front as described below using only the torsion bar adjusters, then see if you still have a DIFFERENCE between Right and Left at the rear which is large enough to worry about.
BEFORE ATTEMPTING TO ADJUST THE FINAL HEIGHTS OF THE VEHICLE AND BEFORE READING THE PRESSURES, cross-level the vehicle at the front. The final height at the rear will be considered later in this post.
What is the purpose of “cross-levelling”?
To explain ….
When the vehicle is on a level surface and with the front wheels pointing straight ahead, then the AHC system causes valves to open and hydraulically connects the Right Front and Left
Front Damping Force Control Actuators (have a look at the diagrams in the attachments to my previous
post – these are the devices to which the ‘globes’ are attached). This means that the AHC pressures in the Right Front and the Left Front are the same. It also means that the Right Front and Left Front of the AHC system are carrying EQUAL SHARES of the vehicle front weight. (By the way, when the front wheels are turned, the AHC system changes the internal valve positions and the AHC pressures in the Right Front and the Left Front ARE NOT the same. This why tests are done with the front wheels straight ahead).
In your situation, we know that the Right Front AHC and the Left Front AHC are at the same pressure and are carrying the same weight because that is how the system works.
If the Right Front height and Left Front height are different, as in your case, then the height difference is caused by the Right Front torsion bar and the Left Front torsion bar carrying DIFFERENT shares of the vehicle weight.
The AHC/TEMS system will not perform correctly and the vehicle may act strangely in this situation. This needs to be fixed by “cross-levelling”.
The purpose of “cross levelling” is to equalise the weight carried by the Right Front torsion bar and the Left Front torsion bar.
This is done with the engine “OFF” and the AHC “OFF” for safety and so that the AHC system does not counteract the adjustments being made.
Note that “cross-levelling” to correct the torsion bar loads CANNOT done by adjusting the Height Control Sensors. If this has been done wrongly or done in the wrong sequence during past work, it will have to be undone as it will have caused wild errors.
Both FIJK and slus have given good advice in earlier posts in this string and slus also has described how to make the “cross level” adjustments. This is usually done by turning the adjusters on both torsion bars in opposite directions until the Right Front hub-to-fender height and Left Front hub-to-fender height are equal.
It can help to move the vehicle (WITH AHC “OFF”) to ensure that the suspension has settled after adjustments, then re-adjust torsion bar adjusters again if necessary.
DO NOT WORRY IF BOTH HUB-TO-FENDER HEIGHTS THEN BECOME WRONG IN THIS STEP. THIS IS TO BE EXPECTED AND IT IS TEMPORARY.
PLEASE DO ONE THING AT A TIME AND IN THE RIGHT ORDER.
AT THIS POINT YOU JUST WANT THE FRONT LEFT AND FRONT RIGHT HEIGHTS TO BE EQUAL BECAUSE THE FIRST AIM IS TO EQUALISE THE WEIGHTS CARRIED BY THE TORSION BARS.
LATER, AFTER THE TORSION BAR LOADS ARE MADE EQUAL BY CROSS-LEVELLING, THE FRONT HEIGHTS ARE ADJUSTED TO CORRECT HEIGHT BY USING THE HEIGHT SENSOR ADJUSTERS.
When the “cross-levelling” is completed, then it is time to turn “ON” the engine and the AHC system. The AHC system will then set the vehicle heights according to instructions the AHC Electronic Control Unit (ECU) receives from the Height Control Sensors - Front Left, Front Right and Single Rear.
If previous work was not conducted in the above sequence, then previous adjustments of the Height Control Sensors will be wrong.
The vehicle heights will be wrong as well. It would not be surprising if all four corner heights are different after correct cross-levelling and all will need to be correctly adjusted.
So, after cross-levelling, the Height Control Sensors will have to be adjusted again to bring the vehicle to the correct hub-to-fender heights measured by tape, at all four corners. It may be difficult to get the Rear Left and Rear Right exactly right. Small differences of a few millimetres hub-to-fender measured by tape are acceptable. Your current difference of 2 centimetres is not acceptable. This will mostly be corrected when the cross-leveling is completed (firstly) and final height adjustments are made (secondly).
Except for cross-levelling, the torsion bars are NOT used to adjust vehicle height in a vehicle with AHC.
NOTE: You do need to be sure that all Height Control Sensors and their internal components are in good condition and operating properly. Otherwise they will be sending incorrect signals to the AHC ECU and cause both height and performance problems and malfunctions – and all you will achieve will be hours of endless frustration! If suspicious, take the Height Control Sensors off, disassemble, inspect, clean up, replace if necessary.
At last -- with the vehicle correctly cross-levelled, hub-to-fender heights correctly adjusted, and with vehicle on a level surface, no driver, no passengers, no luggage or other contents, both fuel tanks full, steering straight ahead --- NOW is the time to have a look at the AHC pressures using Techstream.
Any earlier pressure readings before cross-levelling and height adjustment are completed are NOT comparable with FSM specifications for Neutral Pressures.
Adjust front pressures if necessary, this time using EQUAL TURNS on BOTH torsion bars IN THE SAME DIRECTION until correct Front AHC pressure is reached, aiming at the mid-range of the FSM specification. When one complete turn is made to both torsion bar adjuster bolts, the pressure will change by about 0.2Mpa. This will NOT change the hub-to-fender heights because these heights are controlled by the Height Control Sensors, not by the torsion bars
AFTER completing Front AHC pressure adjustment into the correct pressure range using both torsion bar adjusters, and AFTER again checking the Rear hub-to-fender heights, check the Rear AHC pressure
As you have installed new OEM springs, reasonable Rear AHC pressure is expected PROVIDED THAT all of the above steps in this post have been completed inh the correct order. As you already know, there is no simple method of adjusting Rear AHC pressure. Spacers can be considered – but before installing them, it is best to complete all the above steps to be sure whether or not they are really necessary.
Also be aware that worn bushes in upper and lower rear control arms and worn ‘shock absorber’ bushes would not be a surprise in a 20 years old vehicle which has travelled 400,000 kilometres. The same could be said about bushes in the front of the vehicle – all worth inspecting closely with a torch and poking around, looking for crumbly or cracked bush material. Bushes in poor condition will have a bad effect on the ride. Replacement of bushes should be considered or possible consequences to ride quality must be accepted.
FINALLY, it is time to think about the condition of ‘globes’ (spheres) called ‘gas chambers’ in the Landcruiser Factory Service Manual (FSM).
With vehicle heights correct and with pressures correct, conduct the “HI/LO” test again. If the ‘globes’ are near new, expect close to 14 graduations at AHC tank. If the ‘globes’ are approaching 7 graduations it means end of life of ‘globes’ and all four ‘globes’ should be replaced.
You have asked:
“In regard to the graduations - yes, I know that this is low, but they still keep good pressure - almost in spec. Does that mean anything or still could be shot?”
To repeat, please be aware that the AHC pressures tells
NOTHING about the condition of the ‘globes’. There is no hydraulic reason why pressures would be different in a static test with good or bad ‘globes’ with the same vehicle at correct weight and correct height.
The AHC pressures give an idea of how much load is being carried by the AHC system, with the rest being carried by the torsion bars and springs – and that is all the pressures tell you.
My suspicion is that your ‘globes’ require replacement. The “HI/LO” test
at correct height and correct pressure will confirm that or not. Even if the test under correct conditions shows recovery from the reported 4 graduations to 7 graduations, replacement of ‘globes’ still is indicated.
Changing ‘globes’ is not a difficult job – depressurise, remove old ‘globes’, install new ‘globes’, flush system, job done. Source OEM ‘globes’ from Toyota, Megazip, Partsouq, Amayama, eBay. Source alternatives from UK -- Pleiades or wtv-UK. ‘Globes’ can be expensive so it pays to shop around. Search the many IH8MUD links about ‘globes’ or ‘spheres’.
Last in this long post, we come to ride quality. This is governed by the Toyota Electronic Modulated Suspension (TEMS) system which works alongside the AHC system in your vehicle and is controlled by the same ECU. TEMS controls damping using many, many inputs from sensors all around the vehicle. These inputs include AHC pressures, vehicle speed, vehicle roll, pitch, yaw, steering angle, and others – see attachments provided previously.
Your post #1 says:
“(the vehicle) rides bouncy, springy - really don't know how to describe it. When I drive by speed bump the entire front of the car keeps going up and down for a while and takes some time to calm down. That makes the car uncontrollable and extremely uncomfortable for the passengers. The comfort - sport switch works, and it makes a significant change of the ride but doesn't help for the bounciness. Out of the town and highway, it is somehow better, but city driving is a nightmare, so I am looking for assistance”.
“Also, another question, at the current height - even far from what it should be, I am getting ~4 graduations. I know that lower than 7 marks mean worn spheres, but my pressure looks good and ride is not harsh - totally opposite, could call it springy/extremely soft/weak - does that still means that my spheres are shot?’
You have provided a very clear description of a suspension in which the torsion bars and springs are working but there is very little damping capacity. The suspension is not under control. It is not recommended to drive a vehicle in this condition. Please be very, very, very careful when it has to be driven.
Given two factors
- the likelihood of a poor result from the “HI/LO” test (most likely less than 7 graduations), and,
- your clear description of none or very little damping effect,
then by far the most likely cause of the lack of damping capacity you have described is ‘globes’ which have lost nitrogen gas pressure, and are past their end of life and require replacement.
You have mentioned that:
“I am getting ~4 graduations. I know that lower than 7 marks mean worn spheres, but my pressure looks good”. If you are thinking that correct pressures suggest satisfactory ‘globes’, then that would be completely incorrect.
There are other more complicated and less likely possibilities such as faults in the Damping Force Control Actuators or the Control Valve assembly and possible problems with the AHC pump. However, you have not reported any Diagnostic Trouble Codes (DTC) from Techstream. You have reported that the AHC raises and lowers correctly and presumably you have timed the raising and lowering times and are satisfied these times are correct. A worn-out pump may raise the vehicle slowly and may not raise the vehicle fully. If this happens, there may be height errors.
Anyway, please accept apologies for what has turned into a very long post. The aim is to help you understand the AHC/TEMS system and some of the symptoms you have observed. Hopefully all this information will be of some help. This post should be read together with my previous
post.
