First we need to explain how the AHC works and its design according to whatwe can glean from Toyotas owner material. Our phone call to Toyota got us to the help desk and their information is unfortunately in error and contrary to the manual.
This table from the Landcruiser manual is an overview of what is intended with the AHC system
Toyota says that - If the above load capacity is exceeded then the desired vehicle height may not be obtained even if the height select switch is pushed. And adds If the vehicle height cannot be raised in normal mode and the height control indicator indicates LO this is because the vehicle is loaded too heavily. Under these conditions, drive your vehicle with due care
Loading up the torsion bars
The Toyota manual sets the following loading and towing capacities for the Sahara.
Max towing - 3500 kg
Max ball loading - 350 kg
Gross weight on vehicle should not exceed 3260kg
Kerb weight (from Toyota Website) 2675-2710kg
Therefore max overall vehicle load 550 585kg
The normal method of fitting the Hayman Reese system (simplified) is to -
1. Adjust ball to be same height as the caravan cup (with van levelled).
2. Hook up the van so normal ball load is on the vehicle.
3. Add the torsion bars and adjust up so that vehicle is level again. (GoSeeAustralia does this by measuring the height from under the guards to the ground on front and back wheels. We maintain the same differential after the caravan is hooked up which allows for the vehicle to be proportionally lower for the additional tow ball load.)
But here is the problem. If the vehicle with Active Height Control has its engine running it will immediately adjust the vehicle to level itself without the fitting of the torsion bars.
Secondly, depending on loading, it may go into the low mode (LO) which is about 5-6cm lower than normal height. Further, it appears that the way the Active Height Control adjusts to equalise the vehicle height is to not only raise the back but also lowers the front of the vehicle to match the rear.
So after trial and errorour suggested method of set up on our company Sahara with AHC is:
1. Adjust the tow ball to be same height as the caravan cup (with the caravan levelled).
2. Move the vehicle ready for attaching the caravan and switch off vehicle.
3. Hook up the van so normal ball load is on the vehicle.
4. Add the torsion bars and adjust up so that vehicle is level again.
5. Measure the height of the ball and start the vehicle.
6. Re-measure the ball height, if the ball has lowered turn off the vehicle disconnect the caravan and reset the height of the tow ball on the vehicle up by the difference lowered (on the GSA Sahara this was 5cm).
Hayman Reese hitch fitted with dual cam sway controller
The rest is trial and error depending on the vehicle load and tow ball loading.
If the height changes with say fuel load because of the difference between empty and full as it passes through the sensors limit setting then the tow ball may need to be adjusted to split the difference.
This means a balance depending on the load and fuel use during a trip so as not to be at one extreme or the other.
To use the Sahara as an example on the differences in ball height with ball already set as per the GoSeeAustralia method described above
33cm with caravan hooked on but no torsion bars added
35.5cm bars added and loaded up
37cm after Sahara started
It should be noted that there is a 7.5cm difference in the height of the vehicle from start to finish.
A possible solution could be to add air bags that can be pumped up to take some of the load. This has not been tried but it seems to be a reasonable option for owners who constantly tow heavy loads.
Editor's Note also see: