Thread: Airbag suspension and off-road driving

for those looking at a simple set up for the rear and prepared to run air on board, you could mount a truck trailer height controller. For those that do not know, they are mechanical valve mechanism. If the arm swings up, the inlet valve opens and air is released to the bellow. If the arm swings down, the exhaust opens and air is vented from the bellow. There is a non active range in the middle where the arm can swing and the valves remain closed. so on normal hwy driving where the axle moves with the imperfections, its movement is minor and the height controller remains in the inactive range.

In this set up, fit the height controller on the chassis above the the A frame boss. With a rod between the A frame boss to the height controller. You can buy height controllers that are retarded in their response to input and versions with 2 outputs. The alternative is to put a restrictor valve on the cross axle link (the hose connecting the 2 rear bellows) so it does not instantly cross axle on you. Being in the middle of the axle and as the distance between A frame boss and chassis in a cross axle articulation situation does not vary a huge amount, the valve should remain in the goldielocks range. The same should apply in normal driving with the body roll. the same axle movement is in play, the difference being the body is moving over the axle, not the axle moving under the body. being a height sensitive mechanism, if you load up, the weight compresses the bellow and the valve opens to air up until you hit the preset height. Reverse for unloading. i went down the path of doing this but bit the bullet with the air bag man kit so my theory is untested. They use them on 99.9% of truck trailers in the country and its a common set up to fit the height controller in the middle of the axle like i'm describing. Fundamental difference between a truck trailer and a Defender is the available articulation.

this set up uses lots of air because unlike a ECU and valve block set up, there is no way to recirculate the exhausted air back into the tank or to another bellow. Thus it's best suited to a set up with air on board or a cummins/isuzu that has a compressor running off the engine.

pic of a height controller.

KD2205.jpg

stick your head under a truck trailer and look for yourself. For those thinking to stick one on each corner, big no no. My little brain does not understand the logic, but everything i read its a no no. the common set up is to mount one on each front and a single on the rear as i described. If you want to look into it, RR and Bentley run this set up on their cars in the 60s. if you do it, write up about it, i'd like to know if my research is valid in real life.

Originally Posted by MLD

for those looking at a simple set up for the rear and prepared to run air on board, you could mount a truck trailer height controller. For those that do not know, they are mechanical valve mechanism. If the arm swings up, the inlet valve opens and air is released to the bellow. If the arm swings down, the exhaust opens and air is vented from the bellow. There is a non active range in the middle where the arm can swing and the valves remain closed. so on normal hwy driving where the axle moves with the imperfections, its movement is minor and the height controller remains in the inactive range.

In this set up, fit the height controller on the chassis above the the A frame boss. With a rod between the A frame boss to the height controller. You can buy height controllers that are retarded in their response to input and versions with 2 outputs. The alternative is to put a restrictor valve on the cross axle link (the hose connecting the 2 rear bellows) so it does not instantly cross axle on you. Being in the middle of the axle and as the distance between A frame boss and chassis in a cross axle articulation situation does not vary a huge amount, the valve should remain in the goldielocks range. The same should apply in normal driving with the body roll. the same axle movement is in play, the difference being the body is moving over the axle, not the axle moving under the body. being a height sensitive mechanism, if you load up, the weight compresses the bellow and the valve opens to air up until you hit the preset height. Reverse for unloading. i went down the path of doing this but bit the bullet with the air bag man kit so my theory is untested. They use them on 99.9% of truck trailers in the country and its a common set up to fit the height controller in the middle of the axle like i'm describing. Fundamental difference between a truck trailer and a Defender is the available articulation.

this set up uses lots of air because unlike a ECU and valve block set up, there is no way to recirculate the exhausted air back into the tank or to another bellow. Thus it's best suited to a set up with air on board or a cummins/isuzu that has a compressor running off the engine.

pic of a height controller.

KD2205.jpg

stick your head under a truck trailer and look for yourself. For those thinking to stick one on each corner, big no no. My little brain does not understand the logic, but everything i read its a no no. the common set up is to mount one on each front and a single on the rear as i described. If you want to look into it, RR and Bentley run this set up on their cars in the 60s. if you do it, write up about it, i'd like to know if my research is valid in real life.

I had considered semi automating my rears with something like you’ve posted but with only rear bags fitted two paddle switches on the dash is super easy works just fine for us…..we are full time on the road and use the bags to level up every other night.

Although most time I get us level as I can the each bag pressure on the dash sometime I do get out after a driver er whoops we’ve been lopsided for the last 2 hours of driving.

Originally Posted by W&KO

I had considered semi automating my rears with something like you’ve posted but with only rear bags fitted two paddle switches on the dash is super easy works just fine for us…...

i was of the understanding that paddle (full manual) was not compliant. noting that many people run that including Mick O'May (cal415). As someone that runs height controllers and leaves it to the ECU to do the thinking, it seems to be a bit hit and miss to manually air up to level. Ambient air temps, weight, would all have an impact on what height you get for a given PSI. the air bag man ECU has a level to horizon feature that will level off the car. I didn't pay for the feature but it sort of does it in the basic calibration. When you turn off the car it will level off. Where i park my car there is a indent in the ground from the weight of the car so my pass front wheel sits lower than the drivers side wheel. in the morning when i drive off, the drivers front is dropped in height until the 40sec has passed for the ECU to register the heights are out of spec and level the fronts up. its quite noticeable from the drivers seat that the nose is drivers side down by 2" over the pass front.

i run my carpark height at -1", my standard height at +1" in the front and 0" in the rear and my off road heights are 2" front and rear. all with a press of a button. kind of neat (albeit unnecessary in hindsight).

Originally Posted by MLD

i was of the understanding that paddle (full manual) was not compliant. noting that many people run that including Mick O'May (cal415). As someone that runs height controllers and leaves it to the ECU to do the thinking, it seems to be a bit hit and miss to manually air up to level. Ambient air temps, weight, would all have an impact on what height you get for a given PSI. the air bag man ECU has a level to horizon feature that will level off the car. I didn't pay for the feature but it sort of does it in the basic calibration. When you turn off the car it will level off. Where i park my car there is a indent in the ground from the weight of the car so my pass front wheel sits lower than the drivers side wheel. in the morning when i drive off, the drivers front is dropped in height until the 40sec has passed for the ECU to register the heights are out of spec and level the fronts up. its quite noticeable from the drivers seat that the nose is drivers side down by 2" over the pass front.

i run my carpark height at -1", my standard height at +1" in the front and 0" in the rear and my off road heights are 2" front and rear. all with a press of a button. kind of neat (albeit unnecessary in hindsight).

Hmm, yes there doesn’t seem to a simple answer to what’s legal……

My QLD engineer was happy with manual paddles for a rear only setup, and air bag man also indicated this although from memory wouldn’t put it in writing My engineer said if I was to bag the front he would require it to be fully automated.

When I did my GVM upgrade I went to a different engineer and he was also happy with the controls for the rear bags.

Weight doesn’t change much day to day for us….although ambient temps does impact the ride height, we’ll more so bag air temp impact height as it differs from the ambient temp at start of the day. As we know the air inside the bag heats up and raises the suspension, some times it’s more than more than I think is possible. If I know the suspension is going to work pretty hard I’ll start with the rear slightly lower than level, generally the rear settles slightly higher than the front.

I used to constantly adjust the pressure fo have the rear sitting perfectly, but now I just set to what I think will do for the day and not bother about it too much.

Re: horizon level….a few years ago I visited the air bag man showroom to discuss with the engineers on what I need to bag the front and automated. I also quizzed them about the front shock mounts as they looked very much like the terrafirma ones… I had a bit of a relationship as they sponsored a couple of events (defender day) I ran. As we had just fitted a pop top conversion I asked could the computer could level the car for sleeping when the Poptop was raised and on a slope I.e. level to the horizon, at the time they said nope, not an option……move forward a couple of years horizon level is now a function. I sometimes wonder if I planted a seed that day.

I’d love to fully bag our and have horizon level as it would be the ducks guys for Poptop owner, or even RTT owners….but I just don’t want to invest the dollars for the air bag man full system and engineering.

Getting as much water into the tank as we could as we were heading the Dirk hartog island…….plus it had the other campers scratching the heads when they walked past. One even stopped and asked why my suspension was so high

Originally Posted by W&KO

Re: horizon level….I asked could the computer could level the car for sleeping when the Poptop was raised and on a slope I.e. level to the horizon, at the time they said nope, not an option……move forward a couple of years horizon level is now a function. I sometimes wonder if I planted a seed that day.

ABM uses intelliride controller which is a Firestone product. The horizon level was developed for motor homes, so it would be ideal for what you want of it. its +/- $400 on top of the package price. While flattering to think you were the kernel of an idea, i suspect the US motor home market was the motivator for its development.

happy travels. i wish i could take a few weeks off to get some fresh air in my nostrils.

Originally Posted by MLD

ABM uses intelliride controller which is a Firestone product. The horizon level was developed for motor homes, so it would be ideal for what you want of it. its +/- $400 on top of the package price. While flattering to think you were the kernel of an idea, i suspect the US motor home market was the motivator for its development.

happy travels. i wish i could take a few weeks off to get some fresh air in my nostrils.

LOL, maybe me asking the question hurried air bag man up to source and offer the technology.

I have just returned from an outback trip, did a LOT of work on the 130 prior to the trip and part of this was to fit the airbagman rear air suspension kit. They don't sell direct in Vic (dunno about other states) and directed me to an agent on my side of Melbourne. I chased these people for about 2 weeks with ignored enquiries and non-returned phone calls, can't imagine a version of reality where I would spend thousands of dollars with someone who can't return a phone call for a serious buyer- can't imagine what their after sales support would be like if stuck in a remote area with a failure. I got the details of a second agent on the other side of Melbourne and bought the kit specified for the rear of the 130 Defender with raised suspension. Had to wait for a batch to be made but they arrived in time for installation prior to setting out.

The kit struck me as being well made but poorly designed. The lower mounts are supposed to be installed by inserting two countersunk screws into the base plate and then holding the assembly upright with the screws dangling through the base plate, whilst bolting the airbag to the plate- so that the screws don't fall into the void- then mounting it to the axle whilst being careful to not let the screws fall into the void. Once installed, these screw heads are never going to be accessible without disassembling the bag from the base plate- which will require access to the screw heads! I've been working on cars, trucks and machinery as professional and amateur for over 44 years and I have never to my recollection installed a fastener that was not going to be accessible once installed. The only way to undo those once there was a bit of grit on the threads would be with a plasma torch. Bloody ridiculous. I welded the screws to the plates of course. I wanted to refit my rear sway bar for the trip but this is not possible with the airbags in place.

Found the system good for levelling the vehicle for the basic load, also good for levelling the Trayon camper when setting up which was one of the desired advantages. When we got over to Port Augusta and loaded for the outback with full fuel, food and water I checked the bag heights and pressures. The maximum pressure stated in the installation instructions is 70psi. With the bags at 70psi the 130 was dragging it's arse severely and the bags were sitting on the flanges. I knew from previous weighbridge checks that we were at about 2100kg on the rear axle, well within the 130's specs.
I rang the Brisbane tech support line and discussed this with their phone guy. He got me to measure the bag heights, looked up some tables and told me that with that pressure and that height, I had approximately 997kg on each airbag, then told me I was overloaded! This did not please me. It took some convincing them that the vehicle for which they had specified this airbag setup had a GVM of 3500kg and a maximum rear axle load of 2200kg. After some to-ing and fro-ing they stated that I could increase the pressure up to a maximum of 100psi to keep the bag within it's specified height range (and if that didn't work perhaps I could get some others in my convoy to carry some of my stuff? Yeah right, convoy of one vehicle!). I expected this as I had looked at the Firestone site and found the supplied bellows is spec'd to a max load of 1400kg at 100psi, where they get the 70psi maximum is a mystery.
I found I required around 80 psi to get the airbags to sit within the specified height range. Having settled this, I had no further issues, travelled Googs track and a lot of other terrain with a near-GVM load uneventfully other than having to tighten a fitting due to one side of the vehicle settling overnight.

So my verdict thus far is yeah it's ok but I wish there were a better way.

your comment about load at max psi caused me to pause. Looking at the Firestone specs, the load capacity of the 1T14C-3 (ABM nil lift), -5 (ABM +2" lift), -7 & -8 even though progressively longer bellows, have +/- the same load rating (ie about 1400kg at 100psi). Like you i'm loaded heavy when i go west and i'm yet to notice any adverse behaviours from the rear bellows to the extra weight or PSI required to maintain the set ride height.

Something to consider and keep an eye out on, because the bellow base plate is larger than the coil plate, the leverage on the axle housing mount is greater. i cracked my housing mounts. Found it the day before departing into the Simpson, so it was a blessing. I had Rick Billington make up larger more sturdy housing brackets that i've welded on. He will have the drawings if you found yourself in a similar position or just want to get ahead of the problem.