[FlawlessPlanGarage]

So, I'm a middle-aged dad with a wife and 3 kids. For 10+ years now, I've had this car-guy dream project of buying a late 1930's touring sedan, like a big-body Olds or Cadillac, then putting a modern diesel truck drivetrain and suspension under it, a giant air conditioner, and using it as the family road trip vehicle for vacations like visiting national parks. However, my oldest kids (twins) are 12 already, and I realized a few years ago that even once I started on that project, it would take me 5+ years to actually build it with my full-time+ job and other dadly responsibilities. I woke up one day and realized that I just didn't have enough years with the kids still at home to actually use and enjoy something like that if it took me that long.

So I decided to take a smaller bite at the vision of the dream Family Truckster and shoot for an "easier" version. I spent a fair amount of time thinking about it and narrowed it down to 3 primary criteria:

1. It needed 3 rows of seating
2. It needed to be able to tow 7000-ish pounds comfortably, and when I say comfortably I mean with a chassis and brakes that can handle taking that weight over the Rockies and also enough power to do 80+MPH up the side of a mountain with that trailer hooked up. I've been spoiled by more than a dozen years with big-block 3/4 ton trucks.
3. With that power, it still had to get 25+mpg on the highway when not towing

After thinking about it for a while (this was in 2018 and early 2019), I came to the conclusion that humans had not yet produced a vehicle that would meet all of my criteria, so I would build it myself! Yes, I know that GM's new SUVs with the 3.0l Duramax would pretty much meet the criteria (not really enough power IMO, but respectable), but they didn't exist then, and I don't have $60k+ to spend on one, so I'll slowly spend $60k building this myself instead

I settled on what I felt was my best option - Buying a GM B-body wagon and diesel-swapping to a Duramax 6.6l V8, which I'll almost certainly do some mild modifications to so that I can break drivetrain parts with 800-ish lb/ft of torque. And after several months of searching, I found one in the glorious pre-COVID heyday of summer 2019.

Of course, it was 1300 miles away and had a blown headgasket, so I needed a Flawless Plan to retrieve it:

Yes, I know it would have been MUCH easier to just diesel swap the Escalade I bought...but what fun would that be?

 

[OkDually]

Welcome to DieselPlace

 

[FlawlessPlanGarage]

Welcome to DieselPlace

Thanks!

Curious for any who have experience with the LB7/early Allison 1000 in a swap - if I'm planning mild mods to the LB7 and 800-ish lb/ft of torque in a 4500lb vehicle, should I be doing any trans mods while it's out? In a truck I know the answer would be "yes", but that's a 6500lb vehicle so I don't know if the juice is worth the squeeze in this case. Anyone with thoughts?

 

[OkDually]

Thanks!

Curious for any who have experience with the LB7/early Allison 1000 in a swap - if I'm planning mild mods to the LB7 and 800-ish lb/ft of torque in a 4500lb vehicle, should I be doing any trans mods while it's out? In a truck I know the answer would be "yes", but that's a 6500lb vehicle so I don't know if the juice is worth the squeeze in this case. Anyone with thoughts?

Anytime you do 50-90+HP engine mods you should highly consider modifying the Allison Trans to help support the power.
Mike L. is an Allison Trans Guru and member here.

 

[sportsman7]

Chassis swap with tubs.

 

[77cruiser]

Should be a neat build, good luck with it.

 

[FlawlessPlanGarage]

Chassis swap with tubs.

Hah, too easy! Actually I really want to keep the 3 rows of seating and a stock appearance on the outside, so tubs just aren't feasible, and I don't want to put it on a truck chassis, because I want it to still drive like a sofa, rather than like a truck.

>Update>>

Well, once I had the beast home, obviously the first priority was disassembly and assessment. Here's some stuff that isn't in the video:

The seller told me that it had a blown headgasket. He was a mobile mechanic and had a couple of other cars he was restoring, so he wasn't without knowledge. He said it was pouring white smoke when he parked it. I decided to take the heads off under the theory that I'd maybe fix it and just drive it for a while before doing the diesel swap. I pulled the heads, and frankly they looked great. No obvious issues with the gaskets, the surfaces looked good, even after resurfacing them by hand with a wetstone. HOWEVER, the #8 runner on the intake and head was literally full to the brim with fuel.

So....I think it just had a stuck fuel injector. I could have probably fixed this for $80 or so and had a perfectly good LT1 Roadmaster wagon, and even by the time I was confident in the diagnosis and that the bottom end was good, I could have probably put new headgaskets and injectors and the other "while you're in there" stuff for $300.

But...I didn't want to. I wanted to get on with the project or I thought I would risk never getting it done. So I tore it down.

Of course, my main problems were self- and space-inflicted, and it took several tries to get it into the right position and get the body separated, but here's my main reason for never seriously considering a scissor lift as an alternative to my MaxJax - you can't do this on a QuickJack:

I remain completely smitten by how rust-free this thing is. Between this and the Escalade, I might never buy another used car that isn't from the desert. I don't mind replacing the bushings and A/C parts that go out on the desert cars...not when you can take everything apart as if it was made yesterday.

Hope you enjoy my latest trials and tribulations - anybody want to start placing bets on how much I have to cut out to fit the diesel? I left a preview for the sharp-eyed in this video at how bad it's going to get:

 

[FlawlessPlanGarage]

Update

OK, it's that long-awaited moment - I cut the floor out of the wagon and tried to set it down on the Duramax/Allison combo.

I fully admit that I bought all of the parts and donor cars for this project before taking any measurements. I knew that the Duramax was wide and tall, but I knew it had been put into cars a few times before - though every other time I've seen it, either the turbo sticks out of the back of the hood, or there's no hood, or some other issues.

I also knew that the Allison trans was really large, but I really wanted to use it for a few reasons:

• I've been driving this one behind an 8.1 gas V8 for 6 years and maybe 20,000 miles. The Allison is just a really good transmission for this era. Shifts are smooth but firm, with none of the lazy sloppiness that I don't enjoy about 4L60's and 4L80's. It really elevates the whole driving experience for me - I'm a manual snob, but a really good automatic in a truck works for me.
• I wanted to tow, and I like having a lot of transmission in reserve. By which I mean that I don't enjoy the feeling that I'm really running a transmission on the ragged edge of heat or torque capacity. Every road trip I took in my E38 750iL, I couldn't shake the feeling that the trans was going to let go when I was 300 miles from nowhere, and I hated that.
• Building a 4L80E to actually handle 800-900 ft/lb of torque at like 1800 RPM, and also tow, is EXPENSIVE. Like $8000+. I already had a good 2WD Allison available to me for "free" and to beef it up a little won't be nearly that expensive.

So, to sum it up, I'm stubborn, and I really want to make this work. This video gave me a much better sense of what I'm up against.

 

[paleyjim]

Cool project! Subscribed.
You may want to check out the impalass forum. User Fix Until Broke has a duramax wagon. Check out the "What did you do to your wagon today" thread for most of his updates. Pretty sure he did not use the Allison, though.

 

[FlawlessPlanGarage]

Thanks @paleyjim I did find him - back when I first started the project I couldn't find any evidence of anyone else doing this swap, so it's awesome to find someone who has done it successfully!

Part 4 - Engine mounts attempt 1:

Well, now that we've established that the engine and trans don't really fit under the body, it's time to see if I can mock up some engine mounts and get the drivetrain pushed lower in the chassis.

It doesn't work very well.

As I previewed at the end of the video, I decided to abandon the idea of keeping or modifying the B-Body front suspension. The lower control arms come in too far and interfere with my ability to shove the engine down as far as I'd like, they are too narrow to use the side-mount approach from the truck, and the steering arm goes right through where the oil pan wants to be.

So I did the obvious thing - I bought C5 Corvette suspension and adapters to mate it to custom frame rails. I'm committed now - this is going to make the project MUCH more complex and include much more fabrication, but it creates an enormous amount of additional space, and also takes quite a bit of weight off the front end (which I'm more than putting back via the heavy drivetrain).

I actually bought front and rear suspension because the price was too good and I have a future Corvair-based project in mind for the rear setup - but the Duramaxster is only going to get the front suspension.

That being said, the sofa-like ride and "handling" is still important for me in the final product here - I'm expecting that I might need airbags or some similar method of getting some extra spring rate in the front for the weight. Anyone with experience adding a few hundred pounds of weight to the front of a Corvette and still having good ride quality? 😃

 

[FlawlessPlanGarage]

Well, the day job has taken up a lot of my youtube time lately, but I did get the next installment up just now - chopping the Roadmaster frame in half to convert the front half of the frame to a Corvette!

The key for making this project doable for me was interface adapters to simplify the fabrication, especially for someone who didn't have the whole Corvette handy to take measurements from. You know a product is good when their website looks like this: rick486.wixsite.com/dobbertinperformance
In truth, this is a really high-quality product and I'm impressed. And I'm just a retail customer, no affiliation or compensation even for the potentially dozens of views I'll be getting for his products, lol

 

[FlawlessPlanGarage]

A couple of updates!:

Part 6 - Squeezing the Duramax in with the C5 front cradle

Part 7 - Engine mounts that might actually work!

 

[FlawlessPlanGarage]

A couple more updates!

 

[FlawlessPlanGarage]

Installed a class III hitch from a cool knock-down kit from KDS Performance:

 

[OkDually]

Making some good progress

 

[FlawlessPlanGarage]

And now for a rear axle upgrade!

At some point I decided that I didn't want to risk scattering the GM 10-bolt in the middle of nowhere with my family on board when I gave it the boot and sent 800-900 ft/lbs of torque through it. So, custom Ford 9" to the rescue!

This was a pretty big undertaking, and with several hurdles with parts sourcing (unsurprising these days, I suppose). The wagon also originally came with a much wider axle than the normal car and truck applications, which also made it challenging. As usual, I decided to do everything in just about the hardest possible way...

 

[FlawlessPlanGarage]

Steering challenges! - Part of my goal with the videos is to not sugar-coat anything, but instead to show all (ok,nearly all) of my mistakes along the way and be realistic about the challenges of doing a project at this scale with limited time, tools, skills, and intellect. The steering rack has been a great example of this - getting a location for it was difficult and I really had to butcher the subframe, and then devising a way to bolt it in wasn't easy either. The C5 front cradle made it much more reasonable to fit the engine for width and height, but the steering rack was trying to occupy the same space as the oil pan, and oil pump, and front pulley, and some other things that I kinda needed on the Duramax.

Then, I had to relocate a hydraulic fitting on the rack, and that really exposed my lack of knowledge. I couldn't find much as far as exploded diagrams or solid info on the Corvette steering racks, so I went the old fashioned way and just dived in. That cost me 2 racks, because my first method of moving the fitting was totally wrong-headed, and on my second attempt, I was too focused on the modifications to even bother checking that the C6 rack would bolt in the same way as the C5.

However, as usual, pure stubbornness eventually won out, and I think I have a workable solution:

 

[firestopper]

Cool build.

 

[FlawlessPlanGarage]

Update - the chassis is "done" and off to powerdercoating! In this picture, the transmission crossmember is in place, but the front subframe has been removed. The C5 Corvette front subframe is all aluminum, so I'm not going to powdercoat it.

My local blasting and powdercoating place gave a special price if you could get your chassis in before Thanksgiving, so that they could do a bunch of them together. I wasn't really ready, but it made a good deadline to shoot for, so I scrambled and got a few things completed.

I had to build a transmission mount for the Allison, which I fabricobbled by chopping the stock B-body transmission crossmember in half and then splicing in a chunk of 2x4 steel tube and some plate to strengthen everything.

I also learned, thanks to some commenters on the GM Longroof forum, that I needed to thicken the edge of the receiver tube that I made to help it live longer. After spending a few late-night, last-minute hours doing so, I tested with an actual 2" draw bar - and it didn't fit inside my receiver tube. Something I should have tested a LONG time ago.

It turns out that the ID of the 2.5" 1/4" wall tube I was using was 2.02", and a standard receiver tube is 2.07". That 50 thousandths is a big deal, it's the difference between fitting and not fitting. So, I had to cut off the receiver tube I made, and weld on a pre-made one. Something I should have done from the beginning, since it saved me making a thickened edge or having to drill the hole for the pin.

I fully expect to find more issues like this as I get closer to 'real' assembly, and that I'll end up having to grind off some powder coating to make changes for some of the remaining details like fuel/brake lines, parking brake cables, whatever breaks when I hit it with 900 ft/lbs of torque, etc. But for the moment it feels like progress, and I'll take it!

 

[Oregonnovaguy]

I admit, I didn’t watch all the videos, and please accept that my criticism is meant to be constructive, but it really looks like the front of that chassis is much too weak to support the weight of a Duramax/Allison, PLUS the weight of that Buick wagon! And the Corvette suspension was designed to support 1/2 the weight you are going to have on the front of this thing when you are through. I don’t think I would put my loved ones in this car for a trip around the block, let alone pulling a heavy trailer at highway speeds. Sorry, but maybe there is more than meets the eye that I missed.