Late edits added to correct errors, typos and omissions!
G’day Ted the LX470,
Welcome to the Forum! It looks like you are getting a good handle on how the AHC system works – and it is a great system when it does work -- and like many of us or at least me, the learning process does involve ‘learning by frustration’.
Your post is informative – some comments are interpolated below.
1. Cross levelling and Operating Height measurements by tape
front left height 49 cm or 19.29 inch
front right height 49.5 cm or 19.48 inch
rear left height 52 cm or 20.5 inch
rear right height 52 cm or 20.5 inch
Hub to fender heights look reasonable compared to IH8MUD approximations for Front 19.75 inches or 500 millimetres and Rear 20.50 inches or 520 millimetres (as distinct from the attached finnicky Factory Service Manual - FSM - specifications), maybe you are a tad low at the front, presume you followed the required sequence:
(1) cross-levelled first with engine/AHC “OFF” using only Torsion Bar adjusters to obtain near as possible equal front hub-to-fender static heights to equalise loads on torsion bars, then,
(2) adjusted operating heights using only Height Control Sensor adjusters to increase/decrease vehicle height as required (measured with engine/AHC “ON”, but turn “OFF” for safety while making actual adjustments – easy for adjuster to slip while making adjustments, especially at rear, then vehicle may move suddenly if AHC is operating -- high potential for injury!)
Suggest always be religious about the different adjusters and their purposes. Frustration certainly follows when torsion bar adjusters are wrongly used to adjust height measurements instead of just equalise them (does not matter what the actual numbers are in that step), and/or, equally frustrating when the Height Control Sensor adjusters are wrongly used in an attempt to cross-level the front heights (already should have been equalised in the prior step – and cannot be done anyway by Height Control Sensor adjusters because Left Front AHC and Right front AHC are hydraulically connected and remain at equal pressure when steering is straight ahead – AHC is two channel system, “pumps up” Front and Rear, cannot “pump up” one front wheel in preference to the other).
2. Height Control Sensors
front right -0.1 inch
front left 0.0 inch
rear -0.1 inch
All close to zero, differences very small, readings look good but actual internal condition of Height Control Sensors is unknown without removal, inspection and testing of Sensors (see FSM and IH8MUD posts – this is not difficult).
3. AHC pressures
Presume AHC pressures measured with vehicle in standard condition on level surface, wheels straight ahead, all fuel tanks full, no persons nor freight nor temporary loads/fittings on board, temperature sensor disconnected at AHC Pump per FSM for Rear pressure reading.
front pressure: 6.5 Mpa (FSM-specified range: 6.4 to 7.4 MPa)
rear pressure: 7.0 Mpa (FSM-specified range: 5.6 to 6.7 MPa OR 5.9 to 7.0 Mpa if subtank fitted)
Height Accumulator pressure: unknown?? – expect around 10.5 MPa
It
may be worth experimenting with slight increase in Front pressure to find ‘sweet spot’ for this vehicle, try 1 or 2 clockwise turns on both torsion bar adjusters to take pressures to 6.7 Mpa
Rear pressure is high, needs to come down for better damping:
OPTION #1: Replacement new genuine OEM stock springs plus 30 millimetre spacer plus possible airbags inside coils for infrequent variable heavy loads – this is a suitable solution if the duty of the vehicle is intended to be fairly light and the aim is to maintain best comfort from the AHC/TEMS system.
OR
OPTION #2: Replacement KING KTRS-79 springs – this is a suitable solution if the duty of the vehicle is more arduous and includes fitting substantial permanent or semi-permanent weight including a selection of: rear drawers, refrigerator, front bar, rear bar, sliders, roof rack and roof load, towball weight of camper/caravan, etc.
Explanation:
You could reduce rear AHC pressure by about 0.5 Mpa by adding 30 millimetre rear spring spacers at both sides and remove both third row seats for less than 0.5 Mpa reduction – but these small improvements do not seem worthwhile without replacement of stock rear OEM springs as well. The spacer causes deflection of the spring, thereby causing the spring to exert more force and carry more load at a given height setting, meaning that the rear AHC carries less load and is at lower pressure. This may give better damping at “N” height – but always take care – if there is too little AHC pressure, then damping actually will get worse and the vehicle may feel too ‘springy’. (NOTE: Replacing rear springs or adding rear spacers
does not change rear vehicle height – that is controlled by the rear Height Control Sensor).
If your rear stock springs are original, they certainly are tired and past their best (meaning they have lost some of their ‘springyness’ – technically, they have lost some of their ‘spring rate’ (meaning the pounds of force per inch of spring deflection) has deteriorated.
The maximum load bearing capacity of the AHC system must not be exceeded – see second page of second attachment. The vehicle may sink to “LO” and may refuse to raise if overloaded. (By the way, be wary of the 3,260 kilogram GVM maximum allowable vehicle + contents weight limit in Australia for LC100 and LX470 without approved GVM Upgrade – which is close to impossible with the AHC/TEMS system).
The heavier duty alternative is to replace rear springs with KING KTRS-79 springs. These have a spring rate of about 130 pounds per inch of deflection which is about 37% higher than the spring rate of new stock AHC springs at 95 pounds per inch of deflection.
When KING KTRS-79 springs are fitted to an empty LC100 or LX470 which is not carrying any load, then the load share carried by the springs is too great, the load share carried by the rear AHC is much less than design, rear AHC pressure is too low (my personal experience was around 5.1Mpa initially), damping is greatly reduced and the rear is unacceptably ‘bouncy’.
For an Owner intending to load his/her vehicle with permanent or semi-permanent heavy fittings plus tow a trailer or campervan with a significant weight on the towball, plus carry passengers in the rear, the KING KTRS-79 springs are a good solution to avoid overloading the AHC system, keep the rear AHC pressure in the specified range and have the AHC/TEMS operating correctly in regard to height control and damping characteristics when weight is near GVM.
There are plenty of searchable posts about springs at IH8MUD.
Here is a good post by uHu for some general insights about what happens at the limits of the TEMS part of the AHC/TEMS system.
It is mainly the TEMS system which is responsible for regulating the damping system in 16 steps continuously in real time and providing the comfort and ride quality -- see also the attachment to this message to obtain a clearer understanding of how this works.
4. Condition of AHC Gas Chambers a.k.a. ‘globes’ or ‘spheres’
Results of a current “HI/LO Test” is not reported.
To be comparable with FSM guidance, the “HI/LO Test” must be performed on a level surface with vehicle in standard condition, wheels straight ahead, all fuel tanks full, no persons nor freight nor temporary loads/fittings on board, at correct height and at correct AHC pressures.
For good AHC/TEMS performance, the ‘globes’ (called Gas Chambers in FSM) need to be in good condition – meaning that the “HI/LO Test” gives a good increase in graduations at the AHC Tank when the suspension is moved between “HI” and “LO” --- 14 graduations = excellent (globes are still near new); 7 graduations = poor (time to change ‘globes’). Actually, FSM says change ‘globes’ at 8 graduations in Australia – reason unknown!
Good AHC pressures within FSM-specified ranges tell NOTHING about ‘globe’ internal condition and tell NOTHING about the condition of individual ‘globes’.
Your observations include:
“…. new front globes installed and AHC fluid bleed, these were pulled from a wrecked 100 series sahara”.
“The rear end of the car is however much softer than the front after globes and fluid change going over large speed bumps the front end is fine and the rear does sag a little, with a full tank of fuel”.
The limitation of the “HI/LO Test” is that it can only measure
total displacement of AHC fluid from all four ‘globes’ to the AHC tank, driven by the pressure of whatever nitrogen still remains on the gas side of the diaphragm in the ‘globes’. There is no method available which distinguishes the on-vehicle condition of individual ‘globes’. [Late edit: Maybe this is not quite correct -- the "16 Step Test" could reveal a problematic corner by a felt difference in stiffness -- but how to distinguish between a problem in a 'globe' from a problem in a Damping Force Control Actuator to which the 'globe' is attached?]
The condition of the replacement Front ‘globes’ second-hand from the mentioned wrecked Sahara is unknown unless you have reliable information from the previous Owner. (For non-Australians, the reference to Sahara is about the top-of-the-line LC100 model marketed with AHC in Australia from late-2005 until arrival of LC200 in 2007). If the replacement Front ‘globes’ were original on the source vehicle, they may be near their use-by date. I have a June 2006 Sahara and changed all four ‘globes’ Toyota OEM replacements at 8 graduations at 183,231 kilometres in May 2019 – admittedly a conservative decision made in advance of a long trip with vehicle weight close to allowable GVM. Now at 206,375 kilometres and 'globes' are still producing about 14 graduations at AHC tank -- as they should!
Your unchanged Rear ‘globes’ may be in suspect condition – and that will be difficult to ascertain. In the situation reported, it is quite possible for the replacement Front ‘globes’ to be in reasonable condition and able to displace sufficient AHC fluid in the “HI/LO Test” but mask inadequate condition of the Rear ‘globes’ displacing minimal AHC fluid in the test. Rear softness over bumps is consistent with Rear ‘globes’ past their best and incapable of providing adequate damping performance.
Late edit: Apparent softness (more like thumping) over bumps, especially at low speed, also may be a consequence of mechanical wear such as worn ball-joints, crumbling bushes at front and/or rear control arms, bushes at 'shock absorbers', bushes at swaybars (front and rear), front wheel bearings in need of repack and adjustment, etc.
The observation that
”….the rear does sag a little, with a full tank of fuel” also is a worry. This may be consistent with poor Rear ‘globe’ condition. Rear height is controlled by the Rear Height Control Sensor and not by the ‘globes’, so suspicion about the internal condition of this Sensor also arises.
The following conclusion is offered for consideration, subject to welcome comments from other IH8MUD Members:
- The reported observations cause considerable doubts about conditions of current AHC ‘globes’ and a possible concern about the internal condition of the Rear Height Control Sensor, both of which need to be resolved,
- If the concerns about 'globe' condition prove correct, then re-indexing torsion bars and replacing the rear springs with the King units will not correct the suspected conditions nor enhance performance, and, extra weight will make the situation worse,
- If not already done, careful inspection of suspension and steering mechanical components may reveal opportunities for improvement and a quieter ride.
The recommended next step is become certain about good condition of front and rear ‘globes’ and front rear Height Control Sensors, and the condition of mechanical suspension components and linkages, especially if additional weight and long trips are being contemplated.
There may be other deeper problems in the AHC/TEMS systems but best to address the above matters first rather than speculate prematurely.
Happy for follow-up by ongoing posts or PM if that helps.
