independent suspension failure on Windsor Rapid

Thanks for your followup, I have to agree with you. I was duped in to thinking that IS is better.

At the risk of appearing to high jack the post !!
I read with interest your reply to Gooble's unfortunate problems.( Hope he finds a cost effective solution to get back on the road )
" Independent suspension is a WOTAM on a trailer "
I am in the process of pounding the pavement in the pursuit of designing a small " Off Road " caravan ( around 14ft ) and thought that Independant suspension was the way to go to combat the zillion of Klm's I intend to do on outback corrugated roads ??
I would appreciate your thoughts.

Cheers
Barry

Yes I'd like for information as well. I have just ordered a new van with trailing arm coil independent suspension (with 8 Gabriel h/d shock absorbers) because my lengthy research identified as this is the most suitable for corrugations. I have a friend with a PhD in mechanical engineering who supports the view that shock absorbers are essential to handle the pounding a chasis/van gets from corrugations.
Gooble, can you post a picture of the damaged suspension?
Was it possible your van was overloaded at any time in use?
WAs it leaf spring or coil independent suspension?
What brand of independent suspension was it?
I am just interested to add to my knowledge base, thats all.

Hope all goes well for you in the new set up

Cheers

I want there to be discussion on independent suspension, as I think that it is falsely promoted to be a more robust system for rough roads. Wamuranman, I was led to believe the same...
The failure has obviously been caused by cyclic loading. There are cracks forming on both the trailing arms around where their are welds for the reinforcing plates, and the mounts to the chassis where the trailing arms attach.
This suspension system was manufactured by but is no longer used by Preston apparently, it was coupled with leaf springs and shock absorber. The system looks robust
We have had the van only 6 months and 15000kms, and taken it on a few dirt and rough roads, but not many with long corrugations. Tyre pressures have always been adjusted accordingly, as has speed. We have had the van weighed in, and we are on par with GVM. We are unsure of the previous history regarding this or it's use, and didn't really inspect the suspension that closely when we bought it.
I am just putting it out there to people to do this check, especially if it is an off-road van as previous owners would have obviously bought it to go off-road.

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Thanks gooble - thats helpful to understand what has happened.
I agree these are relevant issues that need to be discussed so that all can make informed decisions.
Can you explain in simple terms what you mean by cyclic loading?
Thanks

if I can put it this way, repeated force on a part or member of a part not too dissimilar to breaking a wire coat hanger by bending back and forward repeatedly until it snaps.
It refers to material fatigue, in this case steel as a result of fluctuating load over time.
Looking at the photo, there is a large distance from the wheel hub back to where the mounts are, causing a significant twisting in the arms. Repeat this twisting thousands of times...

I do thank you for this advice, I will definitely look into it. We have to keep on moving, and a warranty process would probably take too long unfortunately.

You may have a problem with warranty.

As you stated "We are unsure of the previous history regarding this or it's use" then it would be a bit hard to be able to say that it was never used in a manner for which it was not designed to be used.

PJ

Glad you have found your way out of this problem.. may I suggest it may be easier to simply fit a straight axle - with welding/labour etc it should be cheaper and is guaranteed to be straight. Axles (bare) are cheap

Ensure you get Aussie made springs that are matched to the weight of the van

Gooble,

It might be worth giving the parts a really good clean and crack testing them. You can buy a red dye from welding supply shops, which you spray on and then wipe off with a rag. The dye stays in any cracks that you can't see. Then you spray on a chalky coating, which makes the cracks show up.

Once you're aware of the extent of the cracking, which almost always goes further than you can see, a good engineering shop should be able to grind the cracks out, repair them and then weld on some serious reinforcing to stop it happening again.

No point in chucking the whole suspension out if it can be fixed cheaply.

Thanks Keith for this information, but the member has cracked completely through, I would not trust any sort of repair. The part shown in the photo is from the opposite side, (photographed for part identification purposes), we had troubles removing the offending part due to twisting of bolts etc.
Since I have seen the extent of cracking, I no longer trust this system of suspension (at least on a single axle).
We have to weigh up the overall cost regarding this, not just of repair. We are a fair way from Hobart, so towing and accomodation while the repairs are being made have been factored in.

Good call. If the failure is that catastrophic and in evidence on both sides, it's probably a basic design fault. If the goods are not reasonably fit for their intended purpose or not of merchantable quality, you do have a legal claim on the manufacturer. If the thing had let go completely the consequences could be tragic. I'd keep the parts and demand fair compensation from the manufacturer.
Good luck.

ChrisE, not sure what you are trying to say here. First you say that IS is a great design but mine was not.
The cracks that developed are not from welding stress, they are from metal fatigue resulting from cyclic loading. Preston Chassis make for so many caravan manufacturers, I would have thought they were a reputable company if they are still being used. I have no complaints about the design and make quality of the rest of the van and chassis, just that the IS system has some short comings in this case.
Since I started this topic, I have learnt that IS is not the solution for off-road proofing a caravan, and that if people are looking into buying a 2nd hand van, consider a thorough inspection of the suspension if it is IS.

No not so much biased, experienced...this suspension tech, to me, is kindy stuff.

Unfortunately to many others its'a very stressful, expensive mystery.

Yes you are correct about many cars having independent suspension - all my road, race and tow cars for the last two decades have had indy at at least one end; most of them at both - however the geometry, layout and fabrication quality of suspension under just about every Indy-sprung trailer in Oz is DEPLORABLE.

I offer Exhibit A (the pic in this thread): if that was installed under a new motor vehicle/tow car there would be public outrage so why should we accept it under our caravans/trailers? It's a pile of ****. I know 16 year old kids who are already designing and fabricating product better than that and in this age of CAD etc, for any manufacturer to offer us a suspension arm of such pathetic geometry (ie: there is none) and rudimentary third-world dirt-floor quality is a DISGRACE.

Only one or two manufacturers here do a truly acceptable quality of indy suspension and by that I mean well-considerd geometry, quality of construction, serviceability and appropriate spring rate. And even then, if the tow car has one or two live axles... what is the point? A trailer will always follow its hitch..it's not racing at Bathurst. Understeer and oversteer and zero-offset steering geometry and toe-in under brakes and camber gain on bump and handling balance front to rear are non-issues with a trailer.

I almost laugh when I see the big bushwacker style caravans - without exception, they bounce and shake thier tow cars on their indy super-duper trailing arm suspension and splimteen shocks... the tyres are flexing yet the suspension is not. Nothing moves. And that is on-road! I have never, never yet seen one of these with effective suspension, yet they cost seriously good money. Even some of these companies' own demo videos (intended, no doubt, to impress us...?) only show 2-3 inches of travel, at best, with wheels lifted off the ground.

I stand by my statement - Indy suspension under any trailer or caravan is a waste of time and money.

Appropriate spring rate and adequate suspension travel is FAR MORE IMPORTANT than if the suspension is beam or indy - and beam actually offers better geometry (among other things) than 99 percent of indy designs.

I certainly hope Gooble gets back on the road ASAP - the best way is with a beam axle and two new leaf springs. That's little more than four welds, two hours' labour and maybe $1000-1500 in new components. Throw everything else in the bin out the back.

With nice supple springs matched to the weight of the caravan and no crook geometry, Gooble's van will tow/track and handle better than it EVER has.