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Discussion Starter #1
I am shopping for a flatbed truck and I am particularly interested in the Promaster chassis-cab with a flatbed. Since they have only been around for a couple of years, they are out of my price range. I have been wondering about the possibility of purchasing a salvage Promaster VAN, with rear-end damage, (<$10,000) and cutting off the back to turn it into a chassis-cab.

I know that the Promaster van is a unibody vehicle, so it would not be like taking the bed off of a pick-up truck and replacing it with a flatbed. However, as I have studied pictures and illustrations of Promaster frames, it appears that the chassis-cab version is built up from the same frame that is used under the van.

Here is what the Promaster brochure on RamTrucks.com says about the frame(s):

"C--Construction here [van] is body-frame integral—BFI, or unibody; some competitive models employ the more common body-on-frame design."

"D--Ram ProMaster Chassis Cab models are designed with the anticipation that you’ll use formidable upfits which will produce a higher vehicle weight. No worries: we added a super-tough upper underbody structure consisting of a steel I-beam overlay."

Does anyone here happen to have experience with this sort of modification, or know enough about auto body engineering to offer advice? I don't want to create a deathtrap, but, if it were done right, could it be safe?
 

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I'm sure it's possible, but I'm not so sure it would be worth it. There are a lot of truck bodies out there that could easily be converted to a flatbed at a lower cost, with a higher capacity and without so much work. My guess is that you would have to find a Promaster that is wrecked, but still happens to have a clear title. Just about every state requires repaired vehicles that have salvage titles to be inspected before being licensed for road use again. It would be a shame to spend all that time and money rebuilding the cab to be told that they won't certify for use.
 

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There is lots of wiring in the van body too, clearance lights to move, and the chassis cab model or cutaway appears to have a completely different rear frame with the van having outrigger frame tubes and others. I wouldn't give you a certification if I was an inspector unless you had completed an engineering evaluation and submitted it in writing with a CE stamp something you will find very hard to get. If I wanted a yard truck or farm truck for off highway use I would do it in a minute... insurance companies often sell totaled salvage vehicles for 10 percent of book value so for a few thousand $ it would be a fun project. Not for highway use unless I could find someone who had done one.
 

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The conversion Fiat Ducato that should be close to the van should be the "chassis cab with platform".
Are used for the ones that need low floor, for example for horses transport.
How to make your own version safe and road legal?



 

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When I was poking around for used PMs a while back, I crawled all over a chassis/cab pondering something similar to what you are talking about. From what I could tell, they are not too dissimilar. I guess it depends to a certain extent on how much weight/size you intend to carry. If you are going to haul cars or something that's going to push it right up to the weight limit, then I think you're barking up the wrong tree. But if you are just hauling lawnmowers or something like that, I think you would be okay just sawing the body off and laying down some 2x4s. The wiring isn't a worry. Just move each tail light assembly down and mount it horizontally. The rest is just backup cam, running lights, and rear door lock.

On both of mine, the license plate light went out, and the computer recognized this and gives a dash warning and idiot light for "license plate light bulb out". Oddly, it doesn't do this for the headlights! So, you might have to put those running lights somewhere if you want to keep the functionality of the idiot light. Big whoop.
 

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It is certainly possible. There is a break right behind the cab for a traditional frame to be fitted. But there are other companies like AL-KO that sell aftermarket frames with suspension for the Euro Ducato and they literally bolt on - just don't know if they are in the US market now.





Your biggest issue would be getting a steel closure for the back of the cab.
 

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Discussion Starter #7 (Edited)
Thanks to all who have replied!

There is a break right behind the cab for a traditional frame to be fitted. But there are other companies like AL-KO that sell aftermarket frames with suspension for the Euro Ducato and they literally bolt on - just don't know if they are in the US market now. Your biggest issue would be getting a steel closure for the back of the cab.
Those are interesting pictures. If a bolt-on rear frame is available, I would certainly consider it. That sounds like an "easy" conversion. I don't think closing off the back of the cab would be too hard. I'd probably use 1/8" aluminum with a few ribs, to withstand being bumped by cargo.

I guess it depends to a certain extent on how much weight/size you intend to carry. . . But if you are just hauling lawnmowers or something like that, I think you would be okay just sawing the body off and laying down some 2x4s.
If I do this conversion, I'll want to allow for the stated GVWR for the vehicle. I would definitely reinforce the frame, I wouldn't just lay down some 2x4's on the existing frame.

The conversion Fiat Ducato that should be close to the van should be the "chassis cab with platform". How to make your own version safe and road legal?
I need to go talk to my local Dept. of Motor Vehicles office about the legal part.

I wouldn't give you a certification if I was an inspector unless you had completed an engineering evaluation and submitted it in writing with a CE stamp something you will find very hard to get.
Building it, then not being able to register it would be bad! I'll talk to the DMV before I take the leap. I have built my own 5x10 utility trailer and had it inspected for registration. It was not a very rigorous inspection, but I'm sure a car/truck inspection would be more thorough.

I'm sure it's possible, but I'm not so sure it would be worth it. There are a lot of truck bodies out there that could easily be converted to a flatbed at a lower cost, with a higher capacity and without so much work.
I started by looking into ready-made flatbed trucks/vans. I would like to keep things simple, but I usually keep my vehicles for ~10 years, so some time spent on modifications may be OK. I want a van-type cab, to keep the overall vehicle length as short a possible (for easy parking, turning, etc.) while still having about a 12' bed. The most common ones are the Ford E-series and GM Savana/Express. I have also looked into Sprinters. I want to keep the GVWR to 10,000# or less, to avoid having to get a DOT number. (And that will be plenty of capacity for my use.) The Promaster is appealing for several reasons, including front-wheel drive (good for winter in the mountains), tight turning radius, and decent MPG. I'm still looking at ready-made flatbeds, but toying with this conversion idea.
 

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Not 100% sure, but I think those stub frames on the Ducatos pictured above are somewhat different than the regular unibody frame on the vans - they are built to special order for the Euro RV industry, so it might be tricky attaching a new rear frame to an existing van chassis cab.
I have never seen a US version Cab and frame unit - only a few fuzzy pictures in the brochures.
 

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When i was looking to buy a 2nd pm, i saw a few new chassis cabs at around $22k. I havent looked for wrecked ones, and i dont really know that market.

I think its a great idea, but i could play devils advocate. You want 12' of bed, and only need maybe 4000lbs of cargo, and i assume you wont be towing a lot (5000 isnt much tow rating). Why not go with something pickup truck based? Fwd vs 4wd. Seems to me you could buy 2 or 3 of those vs 1 pm.

Not trying to convince you, just putting it out there.
 

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Discussion Starter #10
Not 100% sure, but I think those stub frames on the Ducatos pictured above are somewhat different than the regular unibody frame on the vans . . . .
I suspected that too.

Why not go with something pickup truck based?
I have considered that. Since the vehicle will be my around-town vehicle, as well as my work truck, I would like for the overall length to be as short a possible, while maximizing the cargo area. With a pick-up truck, the overall length, for a given bed size, will be at least 2' longer than a Promaster. I AM considering other van-type chassis-cab vehicles, but the Promaster is my first choice. If they had been in the US a little longer, it would be easier to find one in my price range (~$10,000).
 

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IMO, it would be easier for you to buy a used truck instead of conversion; or just get a new chassis cab - you should be able to get a deal for mid $20's
 

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Keith W, the poster has said his budget is $10K. Whatever the price more will need to be spent to get the truck outfitted.
 

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Time and time again, I have seen attempts to do something the cheap way end up being more expensive than doing it right the first time.

I would not mess with anything that relates to unibody integrity. It's possible that the frame members on the chassis-cab look outwardly similar to what's underneath the van, but the welded-together box of the van contributes a lot of structural integrity that is not there when you chop it away. The frame members on the chassis-cab could be a different thickness or otherwise modified in design to make up for not having a welded-together great big box above them. I don't know if that's the case, but it's highly likely.

There's another bit of ugliness ... corrosion protection. All your chopping and drilling out spot welds is going to expose a lot of bare metal. You are going to have to fabricate something to close off the back of the cab and weld it in place. Nevermind the labour involved - Just the paint job that will be needed will eat up a good chunk of your budget if you want to do it right and for the job to stand the test of time.

If I were the MoT roadworthiness inspector, I'd be skeptical.

If I were your insurance agent, I'd be really skeptical.

In my opinion ... If it's going to be a road vehicle, it's not worthwhile, and not worth the risk, may not be legal, and probably won' be (legally) insurable, at least not in my part of the world.

If it's going to be an off road farm or yard truck ... No license required, no insurance required, no foreseeable risk to the general motoring public ... Hacksaw away and let us know what happens!
 

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Discussion Starter #14
As far as the economics go . . . for $10,000, I could probably get a 2007 Ford E-350 (or equivalent GM) chassis cab + flatbed with ~120,000 miles.

Or . . . I recently watched a salvage auction for a 2014 Promaster with rear-end damage and I think it went for $7,100 (or $8,000 with delivery and fees). It had about 20,000 miles on it. Cutting and modifying the back looks like it might take a few weeks. (I do metal fabrication work professionally, but not usually vehicles.) So, maybe $3,000 worth of work(?). Its hard to estimate, but the idea of ending up with a newer, low-mileage Promaster, for roughly the same price as an older E-350 is appealing.

There are plenty of red flags waving in the back of my mind, but it's tempting.
 

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Discussion Starter #15
It's possible that the frame members on the chassis-cab look outwardly similar to what's underneath the van, but the welded-together box of the van contributes a lot of structural integrity that is not there when you chop it away. The frame members on the chassis-cab could be a different thickness or otherwise modified in design to make up for not having a welded-together great big box above them.
I agree that there could be differences in the chassis cab frame that are not easy to see.
 

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I agree that there could be differences in the chassis cab frame that are not easy to see.
They are very different as far as I can tell -- and I've seen drawings of the chassis cross section for the cutaway. There is a document showing how to extend the chassis at the rear. I'll try to find and post it. As I recall splice plates are used to bolt these sections together.

As mentioned above, in Europe the Ducato chassis is replaced from cab back, sometimes with tandem rear axles to increase GVWR.

From what I can see the van's unitized chassis' main rails is made up of a C channel welded to floor (I've seen similar cross sections being called a "hat" channel), thereby using the floor as part of the structure. The floor closes the channel into a tube.

By comparison, on the cab or cutaway chassis there is a top "hat" channel that is inverted and attached to lower section. The two hat channels combined make like a rectangular tube for frame strength and rigidity.

I suspect that under the cab area where the fuel tank resides, that the chassis is the same on both the van and cutaway. A new frame fabricated from steel tubing would have to attach near this area. Attaching further back would not be strong enough.

Fortunately, detailed instructions show how to bolt a new frame to the cab just about where the PM's floor steps down.
 

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Discussion Starter #17 (Edited)
on the cab or cutaway chassis there is a top "hat" channel that is inverted and attached to lower section. The two hat channels combined make like a rectangular tube for frame strength and rigidity.

I suspect that under the cab area where the fuel tank resides, that the chassis is the same on both the van and cutaway. A new frame fabricated from steel tubing would have to attach near this area. Attaching further back would not be strong enough.
The way you described the assembly matches my understanding (from looking at pictures). My initial thought on converting a van to a chassis cab is to cut away most of the rear body panels, leaving the original lower frame channels in place, with the rear axle attached (and, perhaps, a strip of the floor, if it can't be easily removed from the channel), then weld a piece of rectangular tube (3 x 6, with 1/8" wall?) directly on top of each channel. The additional tubes would then need cross bracing as well.
 

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Discussion Starter #18
The underlying frame of the van, or chassis cab (I think):



With the additional channel welded on top, for the chassis cab:

 
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