Can anyone help with ESC for Hydraulic disk brakes on a <span class="highlight">caravan</span>

RMD of course you are right. The P3 unit merely applies the brakes harder at the touch of the tow pedal when programmed to do so; it doesn't actually respond any quicker.

The reason for raising this is that we just got home from a lap around Oz and our van was unaffected by crosswinds, road trains, uneven roads and so on. It has very soft long travel five link air suspension with long trailing arms, dual vertical shocks and a heavy anti-roll bar. But heading into a southerly down the freeway north of Sydney doing 100kph in the left lane, I could feel the rig move when we were overtaken from behind. This I did not like, even though it did not feel particularly unsafe.

Here's a promotional video on the Lippert Sway Command, which Al-Ko uses.
Lippert Sway Command

It sends the braking signal in parallel to all trailer wheels at once. In my case, the signal would go to the Hydrastar unit instead of to the brake magnets.

I wonder if any automated system, even if slightly compromised by a reduced response time, might be a lot more effective than me sensing the sway and then applying the trailer brakes.

The control box on the chassis is not properly waterproof. so it would need to be installed in an enclosure. At $750-$800, is this thing worth a punt? The insurance savings will pay for it in about five years.

Keith

Keith
I see your predicament. Although the activation of the hydrastar would be from the Alko unit, the brake magnets have to be energised and move and initiate servo braking action of the drums in a drum brake system. The shoes have to be moved a distance, even when correctly adjusted before braking occurs. Maybe the Hydrastar has to spin up it's motor to create pressure but any time loss with the drum brake/magnet system is eliminated and only the Hydrastar lock time becomes the actual application time of corrections made by the Alko. Has to be quick I would imagine. May motor vehicles use a pressure generator as the source of developing braking pressure. No vac booster at all, just a motor and pump which starts when braking is required and pressure modulated to pedal force. ABS uses the same basic source of braking pressure. The Hydrastar is similar.
I like the description of long arm trailing, airbag with roll bar setup as your suspension, good thing, but the turbulence you have noted is happening Frack to Bunt with an overtaking vehicle of sufficient area hitting the rear of the van first and not the other way around as is normally experienced. The flicking would be at a slower rate than the suddenness of an opposite direction travel bow wave/vacuum effect and be minimal as the pressure and vacuum fluctuates as the other rig comes alongside and depends on overtaking speed difference. Does it happen for long, ie, sustained movement or short lived as the prime mover gets past the van rear?
As to the economies of fitting or not, it would be interesting doing it, but to gain an insurance advantage has to be your call. If not really dangerous or heart stopping and also knowing when it is likely, you are already alert anyway.

Maybe I am looking at ESC as a substitute for good design, as many caravan manufacturers seem to do. Here's why.

I already know that my caravan suspension is underdamped, that my hitch pivot is too far back and that my tow ball weight is only 7.8%.

I used LC 100 rear shocks for the build setup and replaced them with new Tough Dog adjustables before registration. These bottomed out and were way too stiff. So I put in four new rear shocks from a Commodore wagon which were a little light-on to start with and the Gibb River Road has now done its worst on them. So I might refit some second hand LC 100 shocks and see how we go.

I am running a McHitch Autocoupler which enables us to hitch up the van without marriage guidance counselling. But it puts the pivot point about six inches aft of where the ball would be. The 200 Series tow already has a big overhang and this can't be helping. I know that the ratio of rear axle-tow pivot distance to wheelbase length should be as low as possible. Maybe I should try a DO35 hitch to shorten this us a bit if the shockers don't solve the problem.

Last of all we have the low tow ball weight. Increasing this can be easily done by fiddling with the three water tanks (400 litres) and the 45 litre grey tank. We normally tow with water tanks full and grey water empty to give a 200kg ball weight. Increasing this is a last resort as the rear axle of the tow is already over its limit. Strangely a Lovels GVM upgrade on an LC 200 does not change the rear axle load capacity. But they still charge you for new rear springs and shockers.

If these things don't fix what is basically a minor problem, I'll go with the Lippert ESC. Here's a video of some of the stuff the old girl has been through. with no dust ingress anywhere.
https://drive.google.com/file/d/1xqju8t2cFWRxUoHzZi9F6kkWagMQTTjB/view?usp=sharing]Bull dust outside Lorella Springs

Keith

The van moving in that scenario will be from air pressure behind the van axle not being resolved through the suspension and tyres to ground. I'm not sure you are going to get ESC that will react to the initial pendulum in any event? When she swings back the other way - sure.
More air pressure in your springs and tyres will help, but as you say your basic van design must be working against you with a fair slab of high side behind the axle of the van catching the wind.
Extending your drawbar won't stop the initial wind effect on the van suspension and tyres, but it will definitely lower any yaw moment being transferred to the tow vehicle, making the tow more stable and lowering your ball weight slightly.
Just thinking out loud.

Keith
If the van is underdamped, that allows the side force of air from the overtaking rig to throw the van and it's mass around on it's suspension, if tightly held in sudden movement the van mass won't alter it's position anywhere near as much. Only if the side force exceeds the tyre grip when side force and van mass movement are kinetically travelling sideways and off line.
GBC has some good points in his reply. Initially the ESC can't do anything until it detects a certain degree of altering to it's set program and detection system. ie it has to begin to fishtail to work! The above shocker control minimizes that in the initial stages of the overtake. Maybe more air in bags will also tighten things but makes it higher unfortunately. Mass up higher isn't so desirable. How 10% became the value of towball weight is like folklore to me. You have to have sufficient, whatever that is to keep the rear axle gripping. Some have far more than 10% and unstable and some less and quite ok.
If the drive axle to ball is minimized then all the better. But that may not be your problem. GBC mentioned longer drawbar, also often good, but that doesn't stop the initial side force of wind pressure, only lessens, to tow vehicle transfer of sway forces.
A GVM cannot ever make an axle rating more, all it does is delve into the safety margin developed by manufacturer of the vehicle.
If you used really good quality shocks on the van , not Crummydore, they could hardly be suitable IMHO, and the LC ones may have lost their initial instantaneous resistance to movement but simply plays catchup when movement happens. A person I know has a LC105 and the shocks do not leak/look good but are stuffed for control ability. Riding in the rear seat is stomach churning for me after 500metres, but vehicle is checked by his 4WD mob who must never really test anything, so he thinks it is all ok. Watch it from behind on the road and it side wobbles. It is dangerous but deaf to comment about shocks. So tow shock rears have to be in top condition along with van shocks. I am super observant with shocks and they would be the very first item I would make sure are actually working on tow and van before anything else. Most places never check shocks and cannot recognize poor performance it seems. Only if they leak do they know something is wrong.
Monroe company had a saying years ago, "don't find out your shocks are worn by ACCIDENT". Read ineffective there too.
PS, with air suspension the shocks become more important than ever because there is no coil or leaf spring mass to absorb any movement and it all has to be controlled by the shock absorbers. If they lag in instant control, then off line it will become.
Mentioned a while back. I replaced my shocks on my 2011 Dmax after it had travelled 5000km from NEW, they still look great in the shed, They just DO NOT control the vehicle axles and body mass. Now different vehicle.

Thanks both of you for some very insightful advice. I agree that the shockers are the place to start. I wanted the van to ride like a limo so that it would not shake itself to death. So I have two 9 inch Firestone Air Bags with 8 inches of suspension travel. The bags are soft, carrying only 2400kg of their 2900kg capacity. Obviously I have fallen down in the damping department, even after three sets of four shocks - two vertical on each side.

Here is a shot of the van hitched up.



You can see that the wheels are set well back and the roof line is low and tapered to the front. The sides also come in at the front. It's bigger than it looks at 14 feet because the top pops up 500mm and there is a 1.5 metre slideout at the back. The taper inwards at the front is a bathroom, with very little weight in it. When loaded and full of water, about 40% of its weight is below floor level. So I think the shape and weight distribution are okay, at least compared to other rigs on the road.

I was running 55 psi in tow rears and van when the "sway" occurred.

So we will start with shocks for sure. I will go ahead and fit some second hand LC 100 ones again to make sure that the fit is right. The Tough Dog adjustables I put in at great expense were supposed to be like for like but had too long a compressed length. I liked them because you can adjust them in situ without removing them. That's why I didn't go for Konis. At least the Monroe Holden Commonwhore ones were on special at Repco when I bought them for jus $100 each.

Thanks again for this most informed advice. Please continue posting if you have any further thoughts.

Keith

It looks very well proportioned. I’m sure it won’t be too much to sort out. Independent single axle vans at any height to tend to waddle a bit. The only other thing I might suggest if you are keen to tinker might be a sway bar for slightly better on road manners but it looks to be far from necessary.

Keith.
You should be very proud of your creation. It is similar to what I proposed to make, with a slide out etc. Just never had the chance. With the good tyres and sensible proportions and not too much rear overhang at all, and weight down low, it would seem to me the issue on any instability would be the shocks unable to retard extension on the side which gets the sudden force, albeit at around 40kmh difference against opposite travel combined speed of probably 140kmh or more. Any lifting of the RHS would transfer weight instantly to other side, so both extension resistance and compression resistance may be important. Many shocks might dampen well but initially allow a fair degree of extension before they slow the action. During that small time frame the van weight will transfer left to some degree. Can you test the opening resistance of the shocks you wish to use with a lever arrangement to get some idea of each shocks initial compression AND extending performance? A few years ago I made a lever attached to my bench so I could gauge, (roughly I know) the initial take up of the action both ways. The ones I tested varied quite a lot. I have 3 1/2 sets of OME for a 60 series and they were supposed to be the ultimate way back then, but I found any degree of solid performance was largely lost after around 35k. I did that because after a while I could feel the loss while driving. Most shock seller will have no idea about what they do. Some do because they are a bit fanatical about performance and have tested them, ie, understand what a shock actually does.

Thanks once more. The setup is actually a solid axle with LC70 front disks, bearings and hubs. The axle is located by two parallel LC100 lower trailing arms 200mm apart and 700mm long on each side. They slope back about 50mm at ride height to minimise bump steer. There is also a Panhard rod and a 32mm diameter anti-roll bar, which I can adjust to stiffen it up a little. We have Nolathane bushes throughout. I went for this setup to give a high roll centre but found that the soft long travel suspension gave horrendous body roll without the anti-roll bar.

I think that you have hit on another good point. The Monroe shockers that are installed are rebound-only. That might be a big source of the problem. That plus the need to stiffen up the anti-roll bar.

You guys have been a major help.

Anyhow, here's a shot of the rig at camp.
Thanks again,
Keith

Keith
Whatever you do with the van suspension, make sure you check the 200's shocks, especially the rear ones. Any loss "or never had " ability will allow the rear of the 200 to move and react to the any movement, normal and also induced by the van. That you will feel! The chap with the 105 definitely has dud shocks and it displays visible wandering over normal road surfaces even when his van doesn't pass anything.

Will do RMD. The current shocks are the Lovells ones that went in with the GVM upgrade a year ago. But I will check them out.
Keith

Allan, Keith.
I agree there will be an effect and the period will be different time intervals for both situations. Initially, as I see it, both will get a pressure hit, then a short suck together or sustained. Keith didn't say if it was sway or a flick and pulled offline for a second or two. Hard to see all in the instant while concentrating. Rear view camera recording might reveal it. The large vehicle is unlikely to move much but the van and tow vehicle will be affected. Perhaps, Keith will have to hammer the sides of the van with a Ball Pein hammer, ie, like a golf ball surface to aid the airflow past the van. Not sure he wants to experiment with that though. Alternatively a wing or flow spoiler, positioned vertically on the corner of van rear may help in that situation if it is sufficient trouble. The closeness of the overtake would have a major effect on severity. High speed trains cannot pass opposite direction unless spaced or slowed.

There is an excellent article regarding wind forces between large vehicles and caravans on Collyn River's site Articles by Others. It is the bottom one on the page.

That article of air movement from passing trucks was instructive and I've seen the effects while watching other rigs on the road.

We have had no problem at all with approaching trucks or from gusting crosswinds. It was only on the last leg of our 30,000km lap that I noticed problems from overtaking vehicles on the 110kph motorways - not just trucks, but larger SUVs as well.

I think maybe the shockers on our van have progressively deteriorated on our trip without me noticing until we were back on high speed roads. The shockers are rebound-only and are now hardly working in rebound at all. I guess that is one of the evils of long travel soft suspension.

I spent yesterday afternoon chasing shock absorber suppliers and it looks like Boss Air Suspension might have something that suits. I'll report back on progress.

Thanks for all of this well informed and constructive help.

Keith

Keith
Because you have airbag suspension, you could Lower the pressure for highway runs and have the van sit lower on the road and the shocks would be not in the same slide position as when inflated for offroad and the mass will be lower too. Less lever action of air/vacuum forces trying to roll the van. Land Rover and Euro 4WD's do similar that and run low at speed for road holding and pumped for offroad. Have to have a selectable pressure system control though.

Firestone, who make the air bags, set a strict tolerance on operating height. Dunno why, but they do. At present we have 100 mm in each direction, up and down. I would not like to reduce the compression distance much below that, given some of the crappy sealed roads we have been down.

Because the caravan is only 14ft when packed up, the floor is only 500mm off the deck, which is much lower than for larger vans, which need a higher platform for their departure angle.

You can see a picture of the rig in an earlier post showing the van not much higher than the tow. I think I am stuck with the height.

Many thanks.
Keith

Keith
Shock absorbers have to control the rebound to some degree, other wise the wheels are fired back onto the road by the spring action, if not controlled that makes for another rebound upward then down and then up and then down until the rebounding stops, if on rough road it never stops and you feel it.
The upward movement has to be controlled too, otherwise there is no mass dampening of suspension movement and perhaps van weight transfer to soften/limit the spring action while under compression.
Be careful who tells you what at Pedders, someone in pedders might know about suspension if you can ever get to talk to that person, but most do not, especially behind the counter sellers of stuff they find in their catalogue system. They may be just pumped up people full of gas and no controlling substance!!!

Ask that person to explain what a shock does and how their product creates the conditions you wish to have as features of your suspension control. A cup of tea, a BEX and a lie down will be needed for him. Watch eyes glaze over, only takes a second or two as they know they are stuffed.

My understanding is a gas charged, oil filled shock has the ability to retard travel speed and force, ie, dampening, in either direction, and because of the internal pressure keeping oil around the piston at all times, they have two pistons, one free and one on the shaft with progression valving, instant retardation of the piston is then available both ways so as to prevent loss of action ability over any time period of travel. The rebound has to be controlled but the force for rebound is only from potential energy stored in the spring unit at that instant. The road force( upward/compression) has to mean more capability for the much greater masses and speeds involved. The shock should lower the wheel to the ground, not allow it to slam. All a science of fluid/mass/energy, heat dissipation. I have never studied all the factors only have some understanding of it. Tech dept of shock companies will know their product and application suitability. ie Experts.
Pedders, probably not. A lot of companies sell shocks rebranded with their own name but are not the makers, some shock maker is the manufacturer.
I like your determination in getting a result. Hard to do with the nong heads in most places.

Keith,

Read an article some years back, re shock absorber characteristics, and it stated that rebound action was 2-3 times stiffer(my word) than compression. In recent times, with better dampening, this ratio may be greater now then what I read.

Re your search for replacement shockies, I have had a good run out of Ironman branded foam shockies, both the 40mm units & the newer Foamcell Pro, a 70mm heavy duty shock. Not sure if you can access something to suit, but good luck.

Bob

I climbed under the van yesterday afternoon to see if there is any way I could get the Tough Dog LC100/200 adjustables I have to fit properly. Because their compressed length is about 80mm too long, I will have to do some major cutting and welding to get them to fit. This will bugger up future maintenance access and will hang them a bit too far below the axle. These shocks had a strong compression and rebound action, unlike the Commodore ones in situ, which are rebound only.

It looks like the second hand shocks I used for sizing during the build were off an early 100 series (not later as I had thought) which were in common with later 80 series. I need a compressed length of 317mm of less and an extended length of about 525. But almost none of the shock suppliers can give me any dimensions and I don't want to order any shocks only to find they won't fit. Been there, done that. But I will keep searching.

On my inspection I did notice that the bracket that clamps the sway bar onto the 100mm RHS axle has migrated about 250mm towards the centre of the van on the driver's side. This would have had a nasty effect on handling. I'll fix that this morning, pull it up a bit tighter and maybe put a keeper weld on the backing plate to stop it happening again. We are heading up the freeway tomorrow and we'll see if this improves things a little. But, as you say, the right shockers remain the big challenge.

Keith

Since we have gone down the shock absorber track, I have started a new thread on shocks. Thanks for your help.
Keith

Keith.
Can't see a shock absorber thread so have returned here.
I have some old and new shocks Some HJ60/61 and some 2011 Dmax cab Chassis.
Both have eyes at each end, which is what you require I presume.
For your info- if useful?
HJ61 rears, eye to eye centres 580 open, 355 compressed. 10 " travel
2011 Dmax rears eye to eye centres 550 open, 350 compressed. 8" travel

Thanks RMD. Apologies for the delayed reply as I have been away. I did try to start another thread on shockers but the computer froze on me and I lost enthusiasm.

Thanks for the offer, but I need studs at the top of the shocks. I have a couple of near new Tough Dog adjustables and am advised that I need only one shock on each side. So I will have to put the van up on stands and weld in some new brackets to suit. The custom ones are $600 each and are now, for me at least, a last resort.

Just on the original question of the Lippert Sway Control. I have been corresponding with the engineer who did the original testing for the importer and I cannot for the life of me see why the Lippert unit will not work with a Hydrastar electric over hydraulic controller. Here's why:

The Brake Controller.
The Tekonsha P3 is on the Lippert "Approved" list and has a setting for electric over hydraulic brakes. Dunno what this setting does. But it has one. So no problems there.

Internal circuit checking.
Every 7 seconds a pulse of 0.013 volts goes from the Lippert control box to the blue wire from the brake controller to see if it's got a load/current draw to check if the magnets (or in the the Hydrastar) are in circuit. If there is an open circuit or no current draw from this test it goes into the error mode. A signal light flashes on the van if there is an error. This testing scenario at such a low voltage should not affect the Hydrastar.

Response time.
The Hydrastar needs about 0.2-0.4 seconds to wake up after braking is called for. Then it takes about 0.75 seconds to hit 200 psi and 1.4 seconds to hit 900 psi, which will give very firm braking but is a long way short of locking up the wheels. That is way faster than the time it would take me to notice the sway, make a decision and to manually operate the brakes.

Proportionality.
Apparently the system calls for more braking, the bigger the sway and then gradually reduced braking as it comes under control. So I don't think there will be a big yank in the pants from a minor sway.

I am going to do a bit of a rework of the suspension with new shocks and brackets, new bushes and brackets for the sway bar and a Airbag Man self levelling kit for the airbags. That's a fair bit of work, so I might install a Lippert unit then as well. If it doesn't work, more fool me.

Thanks everyone.
Keith