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 Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster

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rcktpwrd
Mr Project
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Mr Project



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Join date : 2018-12-15

Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Empty
PostSubject: Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster   Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Icon_minitimeWed Mar 31, 2021 2:27 pm

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:


  • It needed 3 rows of seating
  • 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, and 200-300HP small-blocks were not going to cut it for me
  • 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 Smile



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. Smile  And after several months of searching, I found one in the glorious pre-COVID heyday of summer 2019.

Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster 50993022856_2ec25bf82b_b

Of course, it was 1300 miles away and had a blown headgasket, so getting it was going to be a challenge.  

I should also add that my buddy who helped me buy the donor truck for this project put a condition on his help - he required me to promise to put the project on YouTube:

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Mr Project



Posts : 11
Join date : 2018-12-15

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PostSubject: Re: Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster   Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Icon_minitimeWed Mar 31, 2021 2:49 pm

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.

Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster 51045003833_50a99ee8f2_b

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:

Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster 51045825402_551ca3c422_b


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:

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Mr Project



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PostSubject: Re: Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster   Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Icon_minitimeWed Mar 31, 2021 2:57 pm

And then, finally, I started doing the real cutting on the wagon and trying to see how bad my predicament really was.

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.

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rcktpwrd

rcktpwrd

Posts : 358
Join date : 2019-03-06
Age : 47
Location : Raleigh, NC

Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Empty
PostSubject: Re: Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster   Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Icon_minitimeWed Mar 31, 2021 5:34 pm

Welcome to the forums!

That is one heck of a project!
There is another member here who did a diesel swap.

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Fix Until Broke



Posts : 162
Join date : 2019-04-05
Location : Southeast Wisconsin

Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Empty
PostSubject: Re: Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster   Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Icon_minitimeWed Mar 31, 2021 9:16 pm

Welcome to the club Smile Great minds think alike - https://www.impalassforum.com/threads/what-did-you-do-to-your-wagon-this-week.260225/post-12102686

Curious to see how this progresses - everything you've faced/shown so far is familiar, but there is a lot more in your future as I'm sure you already know.

I'm glad to share any knowledge/tips/tricks/lessons learned/problems faced/etc
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convert2diesel



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Join date : 2009-01-05
Age : 69
Location : Manotick, Ontario

Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Empty
PostSubject: Re: Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster   Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Icon_minitimeWed Mar 31, 2021 10:57 pm

Great choice for a powertrain.  However, you will have to do some major modification to the trans tunnel and the firewall to fit the Ally in and to accomodate the rear turbo and exhaust plumbing.  Actually bought the Cadillac specifically to fit in a rear turbo 6.5.  The engine doesn't sit as far back and under the firewall as the wagons (longer engine compartment )

What are you towing?  The reason I ask is that in the early years, and maybe as late as 2010, the Duramax was available in the commercial vans using a beefed up 4L80 and a slight power reduction in the engine tuning. From what I have heard, it actually made better mileage then with the original 5 speed Allison. Know you want the Ally but the 4l80 can be built to handle the torque for far less than 8 grand.  More like 3 or 4 grand.

Another consideration would be the tow rating on the Buick.  If you plan on towing anything over 5,000 lbs, regardless of the powertrain, you will exceed the manufacturers rating unless you live in a jurisdiction that allows you to change the GVWR of your car.  Big fines in many areas and worse, if you are in an accident, your insurance company may refuse your claim.  This was one of the reasons I went to the Fleetwood.  Had a tow rating of 7,000 lbs.

Was pulled over twice with this combo, even though the combined rating was within the specs.

https://2img.net/h/i156.photobucket.com/albums/t5/convert2diesel/CarTrailer2-1.jpg

Will be following your progress with interest.

Bill

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Mr Project



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Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Empty
PostSubject: Re: Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster   Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Icon_minitimeThu Apr 01, 2021 11:52 am

Fix Until Broke wrote:
Welcome to the club Smile Great minds think alike - https://www.impalassforum.com/threads/what-did-you-do-to-your-wagon-this-week.260225/post-12102686

Curious to see how this progresses - everything you've faced/shown so far is familiar, but there is a lot more in your future as I'm sure you already know.

I'm glad to share any knowledge/tips/tricks/lessons learned/problems faced/etc

That's fantastic! I had seen the 6.5 swap on this forum during the research phase of my project but not yours - I can't believe there's someone else out there as dumb and stubborn as I am! Laughing

I have so many questions for you - but let me start with "what did you do for the oil pan and steering?" I've already committed to a specific direction on this, but I'm really curious as it looks like you kept FAR more B-Body chassis in your swap than I did.

Then I'm curious about the electrical side in general terms - I see you kept the truck steering column, did you do a "standalone" conversion on the engine and trans yourself? Thankfully I have an LB7 so I'm pre-CAN, which I'm hoping will make my life a TINY bit easier.
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Fix Until Broke



Posts : 162
Join date : 2019-04-05
Location : Southeast Wisconsin

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PostSubject: Re: Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster   Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Icon_minitimeThu Apr 01, 2021 12:19 pm

As you can appreciate, there's not a short answer to your questions Smile. I'm glad to discuss in detail, but probably best done over the phone sometime.

You can e-mail me at my username (no spaces) at gmail and we can exchange contact info.

I'll try and briefly answer your questions below...

Oil pan and steering - Custom upper and lower engine oil pans along with crossmember modifications to get the engine low enough so the stock hood closes and the turbo fits under the firewall. This was one of my criteria - looks stock.

Steering is largely stock - only issue that I over complicated (see username) was the center link. There's a crankshaft where the OEM center link wants to be and one solution is to make a "U" shape of it and leave the rest alone Smile. The upper oil pan modifications will allow for full steering travel with stock geometry. There are compromises with this choice though that are lengthy to discuss.

I went with a 6L90E so didn't have to do near the tunnel modifications that you have done (practically none - Just a little hammering by the tailshaft - no cutting, no welding). I do have a ~1.5" body lift (2 jr size hockey pucks) which is all for the transmission clearance. It helps under the hood, but not required.

Wiring - As far as it knows, it's still in a 2012 G4500 chassis with all control modules intact and functional. Everything shows up on the scanner, etc. Only persistent codes are for the mechanical cooling fan control which was deleted. There was a LOT of integration between 1996 and 2012 wiring to make this happen. CAN is no big deal and didn't drive any particular decisions in my case. Having a complete functional running/driving donor vehicle is really helpful - not essential, but highly recommended!

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PatDTN



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Age : 65
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Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Empty
PostSubject: Re: Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster   Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Icon_minitimeSat Apr 10, 2021 7:44 pm

Very cool. I daydream about doing that but I updated my dream to an all aluminum 6.2 LS with the 6L80e. In my dream (never actually planned to do it) I wanted to swap the entire rear end and front suspension to get better ABS and update a bunch of electronics.

With the right gearing it would tow and haul butt.

Love that you followed your dream to reality.

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http://www.patdonahue.com
Mr Project



Posts : 11
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Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Empty
PostSubject: Re: Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster   Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Icon_minitimeWed Apr 14, 2021 8:05 am

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 didn'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 as FixUntilBroke mentioned, 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 decided on this course quite a while ago - so I was committed before seeing FixUntilBroke's version! Obviously it can be done by making different compromises - I may well regret choosing this path, but for the moment I like what the Corvette front end is gaining me in terms of real estate and geometry for the front end.


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 weight to the front of a Corvette and still having good ride quality? Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster 1f600
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Mr Project



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PostSubject: Re: Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster   Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Icon_minitimeWed May 12, 2021 12:33 pm

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: C5 and C6 Corvette Suspensions Interface Adapters :p

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

Overall this phase of the chassis work is really intimidating to me, since there are so many ways to screw it up, but it's coming together and I feel good about the new set of compromises I'll be making.  

Fix Until Broke - you obviously found a way to make it fit with just a small body lift - I wasn't willing to lift the body and just didn't feel like I could make it work in the stock chassis the way that I wanted to.  Your way is definitely smarter but I'm optimistic that I'll eventually make this way work.  Famous last words!
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Fix Until Broke



Posts : 162
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Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Empty
PostSubject: Re: Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster   Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Icon_minitimeWed May 12, 2021 10:04 pm

Looking good - I like those adapters for the C5 subframe. That will be pretty slick!

I don't think there's a better/worse, smarter/dumber, etc way to go about something like this - The fact that we both did it is proof enough that we're not that smart to start with Smile.

Anxiously awaiting the next installment!

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Klaus 95RMW



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Age : 59
Location : Denmark, Roskilde

Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Empty
PostSubject: Re: Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster   Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Icon_minitimeSat May 15, 2021 2:26 pm

Wow buddy... quite a project you have going on. Admire your persistence with this, I would have thrown in the towel many times by now.
A shame chopping up the perfect rust free frame though.. would have paid 2G for that alone any day.. but too late now I guess.. LoL
Keep up the spirit, looking forward for the next chapter.
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Mr Project



Posts : 11
Join date : 2018-12-15

Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Empty
PostSubject: Re: Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster   Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Icon_minitimeWed Aug 04, 2021 8:10 am

Klaus, it's been hard for me to cut up a rust-free wagon as well! But it just made more sense to start with a non-running rust-free example, saves a few hundred hours of rust repair that I can spend on fixing my chassis fabrication mistakes instead Smile

A couple of updates!:

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



Part 7 - Engine mounts that might actually work!
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Mr Project



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PostSubject: Re: Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster   Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Icon_minitimeFri Aug 27, 2021 8:46 am

A couple more updates!




I didn't realize there was a hidden VIN stamped on top of the frame rail, though I assume most of you here already knew that!
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Mr Project



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PostSubject: Re: Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster   Swapping a 6.6l Duramax/Allison into a '94 Roadmaster Wagon - The Duramaxster Icon_minitimeWed Sep 15, 2021 8:49 am

Installed a class III hitch from KDS Performance's DIY kit. Very happy with this setup from Michael, thanks to this forum for helping me find it!

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