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.

[Vimes]

Finally, some progress ! Although, not what I really wanted to see but I'll cover that. These pictures are just a quick mock-up, nothing is welded (just tacked for now) and nothing is placed correctly yet as they needed my input before doing more.



First up, the stock frame is actually 2x4 under the cab, not 2x6 as I thought. And, it's actually a 2x4 C-channel with a very crappily welded box on it. You can see the stock frame in the background of pic 3. At the back of the cab it transitions to a 2x5 C-channel for the underbed portion and Dodge rated it to haul about 1800lbs in the bed. Based on this, we decided that going 2x4 box for the entire frame will be sufficient. I did ask him about hitting bumps and having the cab hit the bed, but he'd confident that this will not be an issue. The truck won't ever be used to haul a load, so this should not be a problem anyway. When this is done the tailgate will no longer open, and it will have a bed cover which will effectively make the bed into a 5ft by 5ft by 2ft trunk.

Now then, for the problem and it's one I don't really get. The truck's front track is 61.4 in, Corvette 61.9 in. The truck's rear track is 62.4 in, Corvette 62.0 in. But, the Corvette cradle has the front tires sticking out too far, like by 3 inches too far.




Both the front and the rear cradles will need to be narrowed by about 6 inches to get the tires inside the fenderwells, and I'm going to have to modify the fenderwells to make room for 10 inch wheels. Not entirely unexpected. I'll also have to flare the fenders a bit to make room for turning the tires up front. This also means I need to source a shorter steering rack. The Corvette steering rack is 27 inches to the A-arm pivot points and I'll need to come up with a 23 inch steering rack now. He'll be discussing this with his fabricator about the possibility of just doing away with the front cradle, but thinks they will have to just use the narrowed ones. I told him to use his discretion on whether or not the front cradle is needed, or if they think it would be better to fabricate something for this.

Based on the wheel tracks I had been hoping that the Corvette suspension would put the wheels where the stock Dakota wheels were, and I could flare the fenders and use wheels with more of a dish. Now I have to find a wheel I find acceptable that fits a Corvette, and there aren't many of those.

Another issue looks like the steering will need to have a mult-link linkage. The picture shows that the steering linkage would have fit perfectly next to the framerail, almost a straight shot, but if it's moved in 3 inches the linkage will run into the frame. But this will be the fabricator's problem. He's pretty good though, so I don't expect this to be much of a problem.

I had thought about using an Aston Martin 8HP90 transaxle and doing a torque tube, but after looking this over I'm just going to do a normal engine mounted transmission. The engine is going to have to ride a bit high on this, but there will be room for it. I'm also prepared to have to clearance the trans tunnel all the way to the back of the cab. For now I'm going to plan on an LS engine with an 8HP transmission. The GM 8 speed doesn't have any aftermarket support, and has problems but the 8HP does have aftermarket support. I'm also running my second vehicle with the 8HP and it's as perfect a transmission as I've ever encountered. Since I'm doing a front trans, I'll have to locate a rear differential now.

But, I'm a happy camper. My project has finally started.

[Vimes]

I found the track widths on the Corvette at the sites below, but internet information is only as accurate as what gets keyed in:

https://www.edmunds.com/chevrolet/co...eatures-specs/
https://corvettestory.com/specs/2003...cs-options.php

The Dakota specs came from:
https://www.edmunds.com/dodge/dakota...eatures-specs/

I would expect that the same site providing information on two different vehicles would at least be consistent in where they're taking the measurements, but perhaps not. The wheel track is supposed to be taken at the wheel mounting surface.

The wheels I'm using (just for the build process) are a set of OE Wheels CV05 in 18x9.5, for a C5 Corvette. Thought they were 18x10s. The offset is 2.12in, backspace 7.38in.

Edit - removed old information.

The shop just called back, and we have a definitive answer now. The Corvette, as you say, measures 71 inches outside to outside on the tires. They took the same measurements and had the same read. The Dakota measures 71.5 inches (whew) outside to outside. Therefore, we'll be running with it like it is. The fenders will be quite a bit closer to the tires with the new suspension, so they will likely need some clearancing/flaring work when I get the truck back. That'll be a helluvalot easier to do than narrowing everything then trying to make all the other stuff fit.

I did briefly consider going ahead with narrowing it up and having room for the wheels (I'm a fan of the old styles) I want, but I don't want to deal with the problems that would cause over an appearance thing. It makes far more sense to keep the suspension stock and supported, and change the wheel appearance. My main thing is functionality, durability and performance, not looks. There are Corvette wheels I find acceptable, just not quite the look I wanted. I'll probably wind up with a 5 spoke mag similar to the wheels I'm using for the build.

What I really wanted, no real specs, but almost 50lbs according to US Mags:


What I was going to go with, 18x10, 5.74in backspace, 20.29lb:

[wfo guy]

That appears to be a Gen 2 compac. I have had several of them. In the summer, you need to run the fan on high or it will freeze over even at lower demands. I have made several trips with these units and after around 75 miles, the evaporator will freeze at low or medium speeds. If all you do is short trips, you won't have this problem. This is only an ac problem. I have visited with the Vintage Air techs on several occasions and have found out that is a downside of Gen 2 units. If you have space, you might consider a Gen 4 unit. I have a 2000 Dakota RT and the blend doors have lost their sealing sponges. I have yet to find a source for those parts. I may do what you are doing but I will look at the larger units to see if that's a good fit. I'm sure the waiting is tough for you. I hope somebody get's in gear to get your truck moving forward. Best wishes on your project.

[ryeguy2006a]

Great update!! Looks like a fun project. I'd like to build a frame someday.

[dontlifttoshift]

The wheel track is supposed to be taken at the wheel mounting surface.

Track width is traditionally measured from the center of one tire to the center of the other tire. As you have learned, that really isn't useful information unless you know wheel sizes and offsets. At that point you can math your way into the measurements that matter.