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Dual Cab Cummins Build

18K views 199 replies 17 participants last post by  nigel3780 
#1 ·
Last year I started another company withthe sole aim to use it to acquire a 4wd that could fit the missus and our new son and take us on some adventure.
I have been borrowing a mates new hilux to go hunting etc, I was thinking of buying a hilux but there is no room in the back seat.
Then I thought I would like a chopped y62 or 200 but didnt want to remortgage the house.
I decided to buy a y61 and either chop it myself or buy one already done.
I searched for about 8 months till I found one I liked and wasnt stupid expensive.
Its a 2007 CRD with leather, sunroof etc.
 

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#2 ·
I decided to get rid of the 3l so I ordered a 4.5 cummins a few weeks ago. Then I listed the motor for sale and sold it for $3300.
So I stripped out the engine and everything else in the engine bay as Im changing the color as well.
 

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#3 ·
A while ago I though I might as well extend the chassis so I can have a decent sized tray so I stripped out the interior and removed the panels.
Im going hunting this weekend so it will be the weekend after when I extend the chassis and repair the body for respray.
 

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#5 ·
Yep, I will update the 'missing the roar' thread when I get home.

The patrol only has 175,000km and is engineered in the ACT for 3550kg gvm upgrade, lift, tyres, chop etc so it was a bonus for me.
It passed inspection at hume no problem too.
 
#6 ·
Being a dual cab owner I will add what I have learned, to try and assist. I have a tourer, so it is not a light weight bush basher. You may know all of this already of course.

Make your extension a good one, the longer the better when it comes to stability in my view.
Brace the chassis right the way along, up to wards the engine mounts. Flex is not your friend when it comes to how the vehicle will ride.
Design your canopy, tool boxes etc to have the heavy stuff like spare wheel and batteries up the front wherever possible.
 
#7 ·
When I bought the ute it came with a set of full chassis bracing. Obviously it wont fit exactly cause of the extension but I can make it work.
I was planning on a 450mm extension which will give me a 2m tray.
 
#8 ·
I would get your tape measure out, work out where your tray will end up, and where the axel will be. Then have a think about how much weight will be behind that axel, rather than centred over it. A 450mm extension will not even be close to getting the axel near the centre of the tray. Getting this right allows the vehicle to ride well. Even the most expensive suspension you can buy will not compensate for too much overhang.

I have discussed this at great length wild Oldmav over the years, with a view to making my GQ work as good as it can. It does not have an extension, and it shows. It simply is not good enough. So I need to fix this when I can afford to do so. I have discussed this with a engineer who is a chassis builder, and has a history of building chassis for race buggy's etc. He now does a lot of 4wd chassis extensions. He advised me that in his opinion, if you want the vehicle suspension to work, you need to keep your overhang to 1000-1200mm. To achieve that, then you need a longer extension than 450mm.

Something to consider anyway. I don't like seeing people make the same mistakes I did, as they are expensive to fix, and make you grumpy!
 
#9 ·
I might have to settle for a slightly smaller tray, to allow a 2m one I would need about a 1m extension to get axle under centre.
I think I would rather a smaller tray than a huge turning circle.
Did you look into extension length and its effect on turning circle?
 
#10 ·
Extensions in the range of 600mm are not uncommon, and would be an improvement. The closer to the sweet spot the better, and the cost will be no different, so may as well get it right. If you have a look at some F trucks the wheelbase is long, with the axel a long way back, no doubt for a reason. I think that moving it around will be determined more by its overall length, rather than the wheelbase. I have seen a 6 wheel lazy axle cruiser running in and out of witches hats to prove the point. Incidentally, rough numbers on a 6 wheel conversion will have the new axle about 1m back from the standard one. Puts a 450mm extension in perspective I think.

Even with my standard wheelbase, and a 1800mm tray, carparks are not my friend. It is a long vehicle, with winch fairlead to tow bar is almost 6m. Not much of a problem for me, as its purpose is the open road for travelling, so it depends on personal needs. And the bigger they are, the more weight too. Mine with a half canopy, and half a tank of fuel and me in it, weighs 3.1T. That includes recovery gear and tools that are in permanently, but no camping gear, or food etc. So if you are fitting a Cummins which is a big lump, an extension with bracing etc, then your GVM is going to need serious consideration. From memory you can scrounge about 3500kg with a GU from some suppliers/certifiers, but more than this is very difficult if not impossible. A lazy axle 6 wheeler would allow 4495kg, as it puts the vehicle in another category.
 
#11 ·
It is already engineered for 3550kg gvm.
It weighs 2490kg empty.
I did some measuring this arvo and a 550mm extension would give me 1200mm overhang for 1800 tray.
And really as its not going to be a daily driver the length isnt going to be too much of an issue. We will just use it for touring and family hunting trips.
 
#12 ·
At 2490 empty it must be almost an empty shell!! LOL.

It is the accessories that add up real fast. My roller drawers and drop down fridge slide weighed over 120kg on their own. Bull bars, tools recovery gear etc all add up. Anyway, you may have less junk than I do.

Touring is where the wheelbase makes the difference. Memory tells me you have good knowledge of suspension. In my experience, excessive overhang past the rear axle causes an effect that leaves a lot like a lack of rebound damping. Makes it quite unsettled, and a series of bumps can be bad. It can be on a downward stroke when you hit the second or third bump, which gives you a hit. So standard wheelbase and 3.5T is not a good combination.

But an 1800 tray and a longer extension will get you closer to a good ride, so that is a step in the right direction I reckon. Here is one way to think about it, just my own personal view. If you eye up a standard dual cab, the tray headboard is right above the axle. In that case, like mine, everything in the tray is behind the axle, which is bad for weight distribution. So if you add a 300mm extension, that is how much room you have in your tray to load stuff in front of the axle, where it is best. But 300mm is not much room to fit all your heavy stuff. 550mm is a lot better. Get the heavy stuff up the front, and the lighter stuff at the back.

Personally I do not get why anyone would go to the trouble of doing an extension, and then only add in 300mm. But 500-700 are the most common from what I remember from my discussions. I am sure you have read the same, but anyone that has done it reports it is a good improvement in the vehicle ride.
 
#14 ·
Well its on the caroliner. Its nearly ready to chop, just have to lock it down.
Ended up going with 550mm extension.
Made the pieces last night,the radius for the top fold on the outside piece is quite large so I will need to massage it to make it work.
 

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#15 ·
Managed to get the chassis extended today.
Tomorrow I have to move the body mount and weld in the chassis bracing.
The cab is also panel beated ready for primer.
 

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#16 ·
Welded in the chassis bracing and moved the body mounts forward today.
The cap is primed and ready to rub and paint.
The engineer will have a look at the chassis this week before we paint it.
Motor vehicle Wood Engineering Gas Machine
 

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#17 ·
Once I get it back home I will have to lengthen the tailshaft brake lines etc. The other thing to do is find a way to mount the sub tank again now that the mounts are 550mm further apart.
 
#20 ·
Nice! I’m gonna have to grind off the bracing on my chassis and start again, yours looks nice.... did you use any internal bracing? Or just replication of the chassis profile then laminate the inside?

my stretch was done in like late 2000’s, then 15 or so years later it rusted a bit and the previous owner to me welded some plates over everything, but they didn’t take off body or canopy so only welded bracing on the bottom of chassis and the heat has warped it.... #facepalm.
 
#21 ·
I didnt use any internal bracing, I just laminated the inside. The engineer was impressed with the job when he came for inspection today.
He just wanted me to weld in a brace between chassis rails when I make the sub tank mount.
I mounted mine on the caroliner so it couldnt move while welding.
It is actually straighter than it came from factory, it measured 3mm long on the passenger side but I trimmed that out when I chopped it.
 
#22 ·
ok cool! I’m not gonna worry about replacing my chassis now, I’ll just fix what’s there.... and build new chassis on next one.

I’ll have to cut my chassis and straighten it.... put new bracing on.... I got a PSR kit with the long arm rear, as I already had the long arms. Any reason you’re not going longarms?
also, I’m pretty sure my tail shaft is using standard f250 bits..... I can get details on carrier if you want.
 
#23 ·
The engineer reckons the tailshaft will be fine as one piece.
The psr bracing doesnt line up with the curve of the chassis or the bolt holes for exhaust brackets etc, so beware you may need to do some mods if you have ocd.
 
#27 ·
The chassis made it back home, I am getting the body ready for painting this weekend so the chassis can have a rest for a week or so.
 

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#28 ·
Made a wheeled trolley out of scrap metal to push the cab round.
Tomorrow arvo I will load it onto the truck and take it to a mates panel shop for painting.
 

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#29 ·
Ready for painting today.
 

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