03 Dakota ext cab

[Vimes]

This project is still going on, but I don't want to jinx anything with an update beyond this. I did want to post up a picture of what I envision though. This is a stolen picture of a random Dakota that I manipulated in Paint to an approximation of what I want to do. And it is a rough approximation, as Paint is a horribly inaccurate way of altering pictures. I've already got a crewcab bed cut down to match the profile of the cab I have instead of the profile of a crewcab. Going with the crewcab bed knocks off 14 inches of truck, and hopefully around 100lbs of weight when the shorter frame is taken into account. It also gives it more of a balanced look vs a longer bed. It's not like I'll be using it as a truck when it's done.

[Vimes]

Checked with the shop yesterday. They finally finished the last project that was in front of mine, and will be getting started on my job now. I went down and went over the particulars, and they're going to start getting the stuff together. I have a couple of questions though.



Will 2x3 square tubing suffice? The truck will essentially be a Corvette with a bed and not used for hauling loads. In fact, I'm probably going to be boxing the tailgate in (found a place that makes carbon fiber tailgates) so it doesn't open and will have a bed cover on making the bed into a trunk. And, offroading is not a thing for me. I'm interested in the lighter weight but not at the expense of being durable.

And, does anyone have a source for chromium steel square tubing? So far I'm only finding 1 inch by 2 inch, which obviously won't cut the mustard. I'd like to find a source for 2x3 and 2x4 chromium steel, suitable for use in a frame.

[dhutton]

Dobbertin adapters need 2x4 tube. I don’t think anyone uses chrome moly for frames. Check with Mike at Cornfield Customs.

Auto weld guys are worthless. Mike is a better bet.

These guys also bend frame rails. https://sschassisworx.com/about-us

I’m sure Donny has some info too. @dontlifttoshift

Don

[ryeguy2006a]

Congrats! Look forward to seeing some updates.

[wfo guy]

I'm using 2x6 and shrunk down to 2x4 for front and rear clips if needed. I would not use anything smaller than 2x4 .187 for main rails with what you are describing. Torsional stiffness is necessary for suspension to work properly.

[Vimes]

dhutton - He's going to mount the suspension direct so the Dobberton adapters aren't needed anymore. I bought them hoping to make it easier on a shop to get the job done but I'll be happy to save the weight. They will be in the For Sale section here in a bit.

Bummer on the no chrome moly bit. I was hoping that chrome moly's strength would let me get away with smaller main tubes. The shop is going to check with their supplier, but if it's not possible I'll probably just go with the mild steel 2x4s. And I'll discuss getting tubes custom bent with him as well. A mandrel bent tube would be lighter than cut tubing with welded plates on the side. Appreciate the recommendation for tube benders, edited my last post to remove the one I found.

wfo guy - thanks. I doubt I'll go 2x6 due to weight, but I'll forget using the 2x3s then.

[dontlifttoshift]

How tall is the stock Dakota frame? Are you adding some other structure that will negate the need for the beam strength of the taller main rails?

[Vimes]

That I don't know and the shop is about 200 miles away. Looking at internet pictures of Dakota frames, it looks like it's boxed in the engine area up to the transmission crossmember, then goes to C channel from there back. I'd say it's 6 inches at least in the C channel area.

There won't be a cage, but there will be cross members and other reinforcement.

I THINK this is a picture of the same frame, but not my actual one.

[dontlifttoshift]

Thanks, that is about what I figured. There is no way I would use less than 2x6.

A car gets a large portion of its beam and torsional strength from the body and roof. That's why early convertibles had extra bracing, or crossmembers, or bigger rockers, etc. to try and hold them together and on a 2 post lift you still can't open the door sometimes. All the crossmembers in the world won't make a 2x4 rail have the same beam strength as 2x6.

[Vimes]

Thanks, I'll discuss it with them, although there are several shops selling C10 frames that are 2x4 steel. The C10 will be roughly the same wheelbase and weight as mine so I may still go with the 2x4.

https://scottshotrods.com/81-87-squa...truck-chassis/ shows a C10 frame using 2x4 .120 for the main rails.

Edit - This has been preying upon my mind so I've done further research into this. I used to have a 79 GMC halfton, which I used to carry stuff in and I know I had more than a ton in the back more than once. The 73-80 Chevy full size trucks use 6 inch C-channel frames. Dodge D10s from the same era use 5.5 inch C-channel. It looks like they use 3/16 steel for this.

Tensile strength for the Chevy frames is 39,000 PSI, using carbon steel. They don't make it easy to find, but from what it looks like 2x4 0.120 cold steel has a tensile strength of 87,000 PSI. I'm confident that 2x4 will be plenty for this project, particularly since I'll be lightening up what I can and the bed will not be used to carry heavy loads; I'm even considering carpeting it.




I'm not going to carpet it.

[ryeguy2006a]

I have no skin in the game, but I'd be listening to the experts here and go with the 2x6" frame rails. I'd think the extra weight could be offset by weight reduction in other areas. I'd go bigger since it's not something that you'd want to redo down the road.

[dontlifttoshift]

I would never use Scotts hot rods as an example of how to do anything.

It's your project, do what you want, but 2x4 rails will be a mistake. There is zero upside to underbuilding this part of the frame.

2x4x.120 is 4.75 pounds per foot
2x6x.120 is 6.46 pounds per foot

You are talking about saving 50 pounds of weight at the very most in the best possible spot to carry some extra weight and giving up half of the rigidity.

It is 100% not about carrying loads and 100% about rigidity. Take a 10' length of 2x4 with jack stands on either end and stand on it and measure the deflection. No imagine that driving down the road. The second "wave" you feel in the truck after every bump is that 2x4 flexing. It'll never fail, as you noted, but it will never drive right.

[Vimes]

You guys are making a compelling argument. Thoughts on 2x6 main rails and 2x4 at the axles? I've also seen 3x4 steel, would this have the same deflection problem as 2x4s? I'm already looking at every possible pound in other areas, and have been eating a lot more salad lately.

[dontlifttoshift]

2x6 main rails and 2x4 at the axles?

That's they way to do it.


RE: 3x4 you have to increase section height to get a meaningful increase in beam strength. That is also why extra crossmembers really don't help but a roll cage helps significantly.

[Vimes]

OK, you've convinced me. I asked the guy doing the work to use 2x6 0.120 for the main beams and 2x4 0.120 over the axles. Appreciate it. Not sure where I'll save the extra weight from, but I would rather carry a little extra weight where it's meaningful. But, the factory frame weighs 542lbs according to Dodge and the new frame will be 13 inches shorter due to my using a crewcab bed behind an ext cab.