D40 Bending chassis

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Prospector

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First up let me say I love my 2008 D40 ST-X, unfortunately I may have to scrap it. I have bent the chassis for the second time and despite being under warranty Nissan are not interested, my insurance company will straighten the chassis again but will not allow reinforcement of the problem area.... result I may have to scrap the thing as IT IS UNSAFE. yes I have ARB upgraded suspension and Airbag man assistors but they (despite claims to the contrary) are not the problem Although they do void the Nissan warranty. The problem is that Nissan have put a a 2.5mm steel box section chassis on a mid size 4WD ute, the weakest chassis of any 4WD ute I have seen in Aust. Seriously have a look at any other ute even other Nissan Utes and they have much stronger chassis. 2.5mm steel rectangular section is nowhere near strong enough to handle the ute let alone hanging an off road camper off it and tackling anything other than bitumen (no potholes of course) is not an option......very surprised this one is allowed on Australian roads such is this critical design weakness.:shoot::shoot:
 

Krankin

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so what guage steel and cross sections do all the other 'stronger' 4wd's use in their chassis'???
 

Soberphobic

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Firstly that sux it happened in the first place. Secondly it seems to happen to all dual cab 4wd's. When researching my suspension upgrade I came across this problem when using airbags. I found examples on different forums of Triton's, Colorado's & Hilux all with bent chassis when carrying loads and using airbags without too much looking. The worst was a Triton towing a camper along the CSR.

For those who haven't seen it the chasis bends around the gap between the cab and tray. The 4wd shop I bought my suspension from acknowledged it as a problem and said they had never seen it happen to a vehicle without airbags and do not recommend airbags on any dual cab.

Here's a link about a Triton
 

Old.Tony

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Welcome to the forum.

I am surprised at this. There are a couple of people on this forum that tow a lot heavier than an off-road camper. I tow an 1800kg full van myself, and I'm not shy about hitting the dirt with it. I think it's Jeff here that has a 2.4T camper AND air bags - his advice (if I recall correctly) was to simply adjust the air bags to suit the load and there's no problem with them.

Of all the chassis bends I've heard of, not a single one of them involved a vehicle that DIDN'T have air bags. Every single one that broke its back had airbags - Navara, Triton, Bravo and Hilux included.

Air bags are a worry, because they don't mount where the chassis has been strengthened to take the weight on the rear. Look at the area where the leaf springs mount to, it's been reinforced. Air bags are often added in front of the axle - and there's no strengthening of the chassis at that point.
 

jayk

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i was out checking my chassis tonight after reading this lol, but all ok so far.... i only run 30 in them when i am heavy, and minimal when i am not towing. at 30 it still sags a tiny bit, but with the lift i dont think you could tell unless you knew what to look for. when i take the trailer off, the rear will rise about 10mm after an hour or two, so the leaf suspension is still doing some work, and hopefully not all strain on airbags and chassis ( a combined effort!) there is a placard on my door seal suggesting up to (i think) 100 psi for a 5th wheeler!
...having said that i am not that mechanically minded, so maybe i have it wrong..
 
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Prospector

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Airbags are set at 30psi suspension is ARB HD leaf pack with greasable shackles. Tub has been removed and replaced with mid strength alloy traywith alloy tube frame with canvas cover. (weight saving of about 300kg over tub) Chassis has a weakened area (chassis flex point between cab and tub) located at the top of the rear wheel arch rise where the foreward tub mounting bracket is located. My chassis bent upwards at this point and was first noticed when the canopy cab gap was seen to be widened. Bend was in the order of 7 deg which was achieved by the vertical walls of the chassis at this point bending outwards (chassis walls became oval). As for other brands, there is a Toyota cab chassi in the next camp site to me in Kalgoorlie and the wall thickness is in the order of 4 to 5mm visualy it appears much stronger and has no weakened/flex areas. Simply looking at a Navara chassis is enough to tell me it is not up to the task. Some good news, the firm who repaired my ute the first time have agreed to straighten and reinforce the chassis (chassis will be plated on vertical walls for a distance of 8 inches both sides of the problem area which should both strengthen the chassis and prevent the verticle walls from bowing out, horizontal walls cannot bow out as they are under compression (bottom) and tension (top)forces in this area) for no cost so I may not have to scrap it might trade it in for a Toyota. Nissan has a bad name in Kalgoorlie as there have been a lot of problems with chassis bending and towbars (even Nissan genuine bars) sperating from the chassis. This is primarily with Utes used in the mining industry so they get a bit of a working over but it is noticable that opinion is almost universal that the Nissan chassis are too weak. Same folks have commented on the problems associated with airbags on nissan and other utes causing compression of the chassis rails where the bags are bolted to the chassis (this has not been a problem on my ute) and a common thread seems to be over inflating the bags to level the vehicle when loaded. Pressures of around 90 psi are not uncommon.
My D40 has ARB suspension, airbagman bags, steel wheels with Cooper ST, rear airlocker, power chip, 4 inch exhaust pipe with Particle filter removed (replaced with section that mounts all Nissan sensors fooling the engine management system into thinking the particle filter is still there and working. Tub has been replaced with alloy tray. Nissan towbar, Nissan bullbar with winch, ARB under body protection (new line from ARB and very strong) UHF, sat nav, EVA COOL fridge behind driver seat. In a box on the tray is compressor, second battery and management system (battery management system connects to camper via anderson plug and talks to the management system in the camper accepting and distributings power from alternator and/or the solar panels on the camper.
So you can see that I have spent a lot on this ute which increases the diapointment that I have been let down by a very weak chassis, something I could not have anticipated.
 

Aussie Frontier

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There are many issues of chassis bending throughout the different manufacturers. The Ford Raptor is bending the chassis from the bump stop on the diff.
The issue here appears to be more a design fault of the airbag manufacturer than Nissan as such. There doesnt appear to be any issues of bending chassis with trucks fitted with bigger springs.
It only appears to happen with trucks with airbags.It pains me to say that Nissan cant be held responsible for an after market part fitted to an area not designed to carry load.If it was a genuine accessory then yes it would be Nissan at fault but an airbag manufacturer designing a bolt on part should take these issues into consideration in their own design.
When I fitted my after market suspension I knew that any damage caused by it would be my own issue and not Nissans. We just have to hope that the persons designing these kits for suspension steering etc has done their homework.
Now all that guff being said I think the design of plating the chassis rails to carry the extra weight from the airbags will end all your issues.With all the work you have already done to your truck just think of this as finally fitting the airbags properly and this is what should have been done in the first place as part of the initial install.
IMO the fault is with the bad design of the airbags

putting my 2 cents on the table

a few pics off the net




All fitted with load helper airbags it would appear
Now the Fords bend
 
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d22dave

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That last photo the tray appears to be out as far as the towball and looking on the phone it looks like the towbar tongue is a fair length which would increase the leverage effect
 

Aussie Frontier

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Yeah when you read the stuff on other forums its a basic design flaw for dual cabs where basically the load is too far behind the axle. It would appear the issue rears its head where you put load on the top of the chassis arch. Air bags or overloaded and resting on the bumpstops does the same thing..In short it looks like the only way is heavier springs but be aware of loading limitations.The fact the manufacturers give us load ratings that might be a little imaginative could be the biggest issue .
I did some reading on the Frontier forum and the issue there isnt from bending the chassis like seen in the pics but the tub hitting the back of the cab. Doesnt seem to bend the rails but they are flexing enough to have the tub hit
 

04SilverSTR

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In my books from what i have seen on the net airbags are a no no for any dual cabs really. Like you have said aussie it puts a pivot point on the chassis where there isnt susposed to be!!!
My 2c
bryan
 

tweak'e

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i can't say the D40 has a weak chassi as ALL mid sized 4x4 use the same sized chassi.

the main problem is that people overload the crap out of double cab utes. toughen up the suspension and fit airbags to compensate, the result being an overloaded chassi which bends/snaps.

its simply a case of too much weight behind the rear axle. as an example, i can load a good 500kg plus behind the cab of my single cab and get the SAME drop in rear suspension as little old me standing on the tow ball.

the further away from the axle you go the more you need to derate you load.
 

KraftyPg

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Overloading is a big issue, very few people even know or remember the load limits the manufacturer puts on their car let alone if they'd changed that limit with their modifications.
 

tweak'e

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its not just the load limits, but how it applies to the vehicle. they tend to forget that the 1 ton load is meant to be distributed over the vehicle, not all sitting on the tow ball.
 

NA_R33

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If welding plates to the chassis rails is illegal why not fab up bolt on braces that wrap around the rails that will spread the load and do the same job as welding stiffening plates in, and be legal at the same time...???

We have been asked to cut some stiffening plates for a panel shop. There customer is fitting air bags to a D40 and addressing the problem before it occurs... Their engineer has called for 3mm plates made from at least 370 grade bisalloy (very high tensile strength) steel.
 

Aussie Frontier

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Dont think it would be illegal to do the welding as such but would have to be engineered as its a chassis modification.A full bolt on kit would do the trick and not need anything

The engineer who passed my truck actually extended his chassis and put the tray from a king cab on the back and its also a hydraulic tilt tray so everything in back is all plated
 

KraftyPg

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its not just the load limits, but how it applies to the vehicle. they tend to forget that the 1 ton load is meant to be distributed over the vehicle, not all sitting on the tow ball.
That's what I was referring too, too many fools think they can whack a tonne in the back and 3 tonne behind and tow up a mountain because they were able to pull the load on the flat bitumen.

Then idiots (especially those in the Holden and Ford utes) go and put low profile tyres on, sports suspension and still think they can skull drag the same loads anywhere their hearts desire because they have a tow bar on the back.
 

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