Dual cab chassis strength

[BROWNY66]

Obviously there are heaps of horror stories of people having a bend or crack in the chassis as a result of airbags or overloading what ever it is. I am looking into a mcc rear bar with single tyre carrier and single jerry can carrier. I don't intend to ever tow an offroad camper and the tub will have an ally and canvas canopy made up soon, including all gear for touring I suppose there will be a couple hundred kilos in the tray. My ute has 200 kg leaf springs in the rear and I want to know if the rear bar with put too much strain on the chassis because of how far back the weight will sit? Very roundabout way to ask a simple question but. Wanted to provide as much info as possible
Cheers

 

[lapsed]

It shouldnt do. I had one on my D22. Took it up the canning with no signs of chassis damage.

most of the issues in regards to the cracking or spliting is the driver.... overloading the tray and add a heavy trailer. and then they pump up the airbags to sit level. reducing the suspensions abillity to do its job. ultimately something has to give so the chassis does.

Hope this helps

Chris

 

[BROWNY66]

Yeah thanks for that, that's what I had read as well in regards to the airbag pressures. Good to hear someone that has had experience with that bar. What suspension did you have in the rear.
Cheers

 

[lapsed]

I'm Running blue max HD leafs and shocks, had a front shock develop a small leak after my big trip other wise, they are doing well.

chris

 

[ben85]

mate i reckon you'll have no drama's at all doing that.

i think you would be best off with heavy duty leaf springs though.
what can happen when your leaves are too soft is they bottom out and the rest of the weight and stress goes through the chassis as there's no give left. it would be like trying to bend something by levering it over a solid object, compared to trying to bend something over a spring which isn't going to be easy ad the spring just compresses under the load, it wont bend til there's no more give left in the spring (which is when your springs are sitting against the bump stops)

 

[BROWNY66]

From my understanding of the leaves I have in now is that they are a constant 200 kg load which will keep the tray level then any extra weight will get taken up by 'helper springs' does that sound right?

 

[180degrees]

mate i reckon you'll have no drama's at all doing that.

i think you would be best off with heavy duty leaf springs though.
what can happen when your leaves are too soft is they bottom out and the rest of the weight and stress goes through the chassis as there's no give left. it would be like trying to bend something by levering it over a solid object, compared to trying to bend something over a spring which isn't going to be easy ad the spring just compresses under the load, it wont bend til there's no more give left in the spring (which is when your springs are sitting against the bump stops)

That depends on if the force required to compress the spring is more then the chassis's bending moment.

but what are the odds of that happening, pretty low imo.

 

[bods]

I'm not sure what distance there is between the rear shackle and the end of the chassis on the d40's but generally the issue of bending the chassis with airbags is because of the point load caused by the airbag in the chassis. The advantage with leaf springs is how far they spread the load out. Even coil gu patrols had a lot of issues breaking coil mounts when loaded up on very rough roads.

With what you are planning to carry you will be fine, you wouldn't be the first to do it and probably not the last.

 

[BROWNY66]

Cheers for the feedback lads. I just needed that reassurance from others so I didn't talk myself out of buying one haha

 

[180degrees]

I'm not sure what distance there is between the rear shackle and the end of the chassis on the d40's but generally the issue of bending the chassis with airbags is because of the point load caused by the airbag in the chassis. The advantage with leaf springs is how far they spread the load out. Even coil gu patrols had a lot of issues breaking coil mounts when loaded up on very rough roads.

With what you are planning to carry you will be fine, you wouldn't be the first to do it and probably not the last.

pretty much this.

airbags create a point load on the chassis, just like a see saw with 2 people on it.

 

[gadgets]

My d22 has 240000k on it, still original leaf springs, only just changed original shocks,has a canopy ,steel roof rack and a 2 tonne trailer everyday. Ive had air bags for the last 40000k, usually pumped to 40psi, no problems.