Readers of this forum will know that I have been searching for the solution for an over weight 2005 TD Sahara, after I put an ARB Delux bar on the front with a Warn winch and a rear bar with a Wheel Carrier and Fuel carrier. The following is the epistle for finding the solution with the traps found along the way. I would like to thank uHu in Norway and Jim_Chow in the US for their contribution on the details of the Active Height Control (AHC) system.
Before I purchased the vehicle I sought assurances from the Toyota people about the addition of the aforementioned accessories. I was told that there would be no problems, as an "ARB /Toyota bar" is fitted as a standard if required, and ARB are "famous around the world". Good, I thought should be no problems here.
Well that was the beginning of my trek.
The vehicle had a problem on delivery of the AHC system where it would raise to the High position on its own accord. Upon taking it to the dealer, they blamed the accessories that I had put on it. Trouble is, it was doing it before they were added. They didn’t believe me. Unfortunately it was then that I discovered that the service blokes did not have a clue about this AHC. I needed to figure out how it worked. Fortunately the rough roads on the Island sorted the problem. Within 3 weeks of the vehicle being here the problem disappeared. Worse was to come.
I discovered that the 220kgs of accessories impinged considerably onto my carrying capacity. The vehicle can carry 540kgs according to the specs. If the vehicle senses it is overweight it drops to the low position. After much searching I discovered that this was a problem with the LX470 and it was going to be more of a problem for me because of the accessory weight. I could only put another 320kgs in the vehicle including a driver. Trouble is, it gets worse than that. Putting 300kg ball weight actually offends the suspension even more. This has to do with moments and leverage over the rear axle. As the 300kgs is back about a meter from the axle the force on the axle is considerably more than 300kgs. And this is where the sensors are. In a normal LC, that doesn’t matter. On a smart Sahara or LX470 it is significant. It won’t like it.
It will spit the dummy and drop to the Low position and stay there until the problem is rectified (weight removed). The problem has, to a degree, been hidden, as presumably not many LX470s do much work in Oz. Moving the AHC system to the 100 LC Sahara is about to change that.
My particular circumstances are that besides the 220kg of accessories I needed to put stuff in the back for travelling (Fridge, drawers, food) and a bit of other gear. I also needed to pull a camper trailer with about 100kg of ball wt. It would do all this except if I put 3 people in the back. It would sulk, especially if the vehicle was filled with fuel.
I needed to find a solution or buy a Discovery 3! (It has ~200kgs more carrying capacity)
I checked out springs and spring manufacturers. Interestingly enough none of them wanted to know when they found that the vehicle was fitted with the AHC system. Nobody new what the spring rate was for the coils, including Toyota. So that made it a bit tricky. After much thought and figuring I decided that putting heavier springs under it would not solve all of my troubles and may in fact cause me more grief than currently is the case. I suspected that heavier springs would not allow the vehicle to drop as it should under certain circumstances. I suspect that it would also raise the rear higher than it currently is under normal loads, which I did not want to happen. So all in all, a blind alley.
Then I checked out the likes of the Polyair bags. However these had a number of problems. Firstly I would need to cut a 40mm hole in the coil tower for the airline. Given the grief I had had with Toyota over the bars, doing this would have had me expelled. Secondly the Poly bags have a set length around the suspension normal ride height. This is fine for normal suspensions where you are trying to keep the suspension at that ht. However with the AHC when you try and lift the vehicle, the airbags lift off their seats and no longer assist the suspension in lifting. So that was not going to work.
I then checked out replacing the coils with an Airbag. This is something we had done with our tandem drive truck (a 1970 White with a V8 GM and a Hendrikson suspension) and it worked a treat. We could match the load to the suspension.
I have just fitted the bags and it works. In the unloaded situation the bags have 16 psi. This is a starting point at which all seems to work well. It will need to be more objectively set with measurement of AHC system pressures. As far as I can figure, I will need to increase the pressure 1psi for every 26kgs of load. I will only do this when travelling, maybe take it up to 26 psi. The interesting thing about these airbags is that they don’t behave the same as coils, which for the AHC makes them ideal. Coils will have a spring rate which in essence says that the greater the compression the greater the opposing force. So as the AHC lifts the vehicle, the higher the vehicle goes the less the coils actually assist. The airbags however, over their working range of about 6 inches, have a "flat" response. Their lift is nearly constant and does not appreciable decrease as the vehicle rises. Just what I needed.
The technical details that I used to figure what was going on are below with some other useful bits and pieces.
Pictures attached of the airbags in the high, normal and low modes.
Donald
Before I purchased the vehicle I sought assurances from the Toyota people about the addition of the aforementioned accessories. I was told that there would be no problems, as an "ARB /Toyota bar" is fitted as a standard if required, and ARB are "famous around the world". Good, I thought should be no problems here.
Well that was the beginning of my trek.
The vehicle had a problem on delivery of the AHC system where it would raise to the High position on its own accord. Upon taking it to the dealer, they blamed the accessories that I had put on it. Trouble is, it was doing it before they were added. They didn’t believe me. Unfortunately it was then that I discovered that the service blokes did not have a clue about this AHC. I needed to figure out how it worked. Fortunately the rough roads on the Island sorted the problem. Within 3 weeks of the vehicle being here the problem disappeared. Worse was to come.
I discovered that the 220kgs of accessories impinged considerably onto my carrying capacity. The vehicle can carry 540kgs according to the specs. If the vehicle senses it is overweight it drops to the low position. After much searching I discovered that this was a problem with the LX470 and it was going to be more of a problem for me because of the accessory weight. I could only put another 320kgs in the vehicle including a driver. Trouble is, it gets worse than that. Putting 300kg ball weight actually offends the suspension even more. This has to do with moments and leverage over the rear axle. As the 300kgs is back about a meter from the axle the force on the axle is considerably more than 300kgs. And this is where the sensors are. In a normal LC, that doesn’t matter. On a smart Sahara or LX470 it is significant. It won’t like it.
It will spit the dummy and drop to the Low position and stay there until the problem is rectified (weight removed). The problem has, to a degree, been hidden, as presumably not many LX470s do much work in Oz. Moving the AHC system to the 100 LC Sahara is about to change that.
My particular circumstances are that besides the 220kg of accessories I needed to put stuff in the back for travelling (Fridge, drawers, food) and a bit of other gear. I also needed to pull a camper trailer with about 100kg of ball wt. It would do all this except if I put 3 people in the back. It would sulk, especially if the vehicle was filled with fuel.
I needed to find a solution or buy a Discovery 3! (It has ~200kgs more carrying capacity)
I checked out springs and spring manufacturers. Interestingly enough none of them wanted to know when they found that the vehicle was fitted with the AHC system. Nobody new what the spring rate was for the coils, including Toyota. So that made it a bit tricky. After much thought and figuring I decided that putting heavier springs under it would not solve all of my troubles and may in fact cause me more grief than currently is the case. I suspected that heavier springs would not allow the vehicle to drop as it should under certain circumstances. I suspect that it would also raise the rear higher than it currently is under normal loads, which I did not want to happen. So all in all, a blind alley.
Then I checked out the likes of the Polyair bags. However these had a number of problems. Firstly I would need to cut a 40mm hole in the coil tower for the airline. Given the grief I had had with Toyota over the bars, doing this would have had me expelled. Secondly the Poly bags have a set length around the suspension normal ride height. This is fine for normal suspensions where you are trying to keep the suspension at that ht. However with the AHC when you try and lift the vehicle, the airbags lift off their seats and no longer assist the suspension in lifting. So that was not going to work.
I then checked out replacing the coils with an Airbag. This is something we had done with our tandem drive truck (a 1970 White with a V8 GM and a Hendrikson suspension) and it worked a treat. We could match the load to the suspension.
I have just fitted the bags and it works. In the unloaded situation the bags have 16 psi. This is a starting point at which all seems to work well. It will need to be more objectively set with measurement of AHC system pressures. As far as I can figure, I will need to increase the pressure 1psi for every 26kgs of load. I will only do this when travelling, maybe take it up to 26 psi. The interesting thing about these airbags is that they don’t behave the same as coils, which for the AHC makes them ideal. Coils will have a spring rate which in essence says that the greater the compression the greater the opposing force. So as the AHC lifts the vehicle, the higher the vehicle goes the less the coils actually assist. The airbags however, over their working range of about 6 inches, have a "flat" response. Their lift is nearly constant and does not appreciable decrease as the vehicle rises. Just what I needed.
The technical details that I used to figure what was going on are below with some other useful bits and pieces.
Pictures attached of the airbags in the high, normal and low modes.
Donald
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) The only time I have had the suspension overload was with a 2500 pound trailer, 3300 pound tractor pushed to the very front of the trailer and put well in excess of 1000 pounds of tongue weight on the vehicle. It did drop into low mode and flash repetitively calling me an idiot so I moved the tractor back to its proper placement over the tandem axles and towed it without further drama. That is an awesome solution with the airbags. 
