Will's Bug Out Rig: Duramax Van

[The Dark Side of Will]

I want to be able to load it up to its GVW without bottoming the suspension.

However, the PN listings I've seen show the same torsion bar used on 1500, 2500 and 3500 pickup trucks... Hollander also thinks they're interchangeable, as looking up 3500 truck torsion bars on www.car-parts.com shows results from 1500 trucks. I guess both could be wrong, but I think that's unlikely due to the potential liability.

I'm open to arguments based on GAWR that the vans just don't need as much front spring rate as the trucks.

Either way, it's not hard to change once I put it together.

[The Dark Side of Will]

Following a bunch of reading over at DieselPlace:

Sooo... Big picture for Diesel 4x4 Van:

1. Reorganize Diesel Fuel Pallet (Skip for gasoline van)
   1. Move fuel cooler in front of cooling stack next to factory aux transmission cooler (do all years have factory aux transmission cooler?)
   2. Replace priming pump with lift pump (Kennedy or similar). Pumps must be mounted out of the way of both the torsion bars and future transfer case. High on the frame rail would do this, but then requires pump to pull fuel up from the bottom of the tank. Can be mounted low outside the frame rail in front of or behind diesel aux battery?
   3. Relocate fuel filter (Need to look at where it can go)
2. Convert front suspension from coil springs to torsion bars
   1. For my 2006 van, I looked up 2006 pickup truck control arms. They look like they'll fit and it looks like that's what Quigley used. I do not know if vans can use 2011 and newer pickup truck control arms or if vans are limited to 2010 and older pickup truck control arms.
   2. I will start out with the 1500 van torsion bars. If I need a higher rate in the front suspension, I can install pickup truck torsion bars which are much stiffer. For some years of truck, GM used the same torsion bar across 1500, 2500 & 3500 pickup trucks, so I don't think that using 1500 van torsion bars in my 3500 van is weird by comparison.
   3. I will start out with the 1500 van torsion bar crossmember. Just like the torsion bars, the trucks use the same torsion bar crossmember from 1500 through 3500. The truck and van crossmembers are very similar dimensionally, so I'm confident the 1500 crossmember will be fine in my 3500 van. The van crossmember also fits easily between the van frame rails and only requires welding on mounting tabs.
3. Install the front diff
   1. The only way to install a front diff without cutting is with a 5+" suspension lift.
   2. The 2011+ pickup truck front diff has less "stuff" poking out of it than the older diff, and looks easier to swap
   3. The Quigley conversions put the bodies of the inner CV joints just under the lower surfaces of the frame rails. This is as high as the diff can reasonably be mounted in the frame. I need to take measurements from my 2011+ diff (as well as get the actual diameter of the inner CV joints) to see what will interfere with what when the diff is in place.
   4. The bolt-in crossmember must be removed
   5. The "corrugated" stampings that mount the bolt-in crossmember and the lower control arm rear pivots mount to must be cut extensively. The pockets to which the bolt-in crossmember mounts must be removed completely. The inboard "point" of the control arm pocket on the driver's side must be cut off.
   6. The engine mount structure sits on top of the corrugated stamping. The mount structure consists of a "tower" that bolts to the corrugated stamping and supports the rubber mount ~4" off the corrugated stamping, as well as an arm that bolts to the engine block and reaches out to sit on top of the rubber mount. At least the tower and maybe both arm and tower will have to be modified or redesigned to allow clearance for the diff.
   7. Once top-side clearance has been made, the 2011+ diff can be mounted entirely from below by custom built subframe or frame rails. Because of the torque involved, especially if using a low range T-case, the mounting structure should bolt hard to the diff mounting points and be rubber mounted to the frame
   8. Once the diff is in place, the frame rails will have to be reconnected with a new crossmember to replace the bolt-in crossmember that was removed for diff clearance. This may carry rubber bushings for the diff mount structure, but should be bolted or welded to the frame and not be rubber mounted, as the original was bolted directly to the frame.
   9. An alternative method is to use the 1500 AWD van bolt-in crossmember. This crossmember provides mount locations for the aft diff mounts and clears the diff snout, but will require welding extensions to the bottom edges of the control arm aft pivot pockets in order to bolt on.
4. Install the axles
   1. The 2011+ diff uses an 8 bolt flange for the inner CV joint. The 2010- axles have a 6 bolt flange. I have not done any investigation to see if there is enough plunge in the inner CV joints to accommodate an adapter plate between the 8 bolt drive flange and 6 bolt inner CV joint.
   2. The 2010- axles have 33 spline outer CVs. The 2010- pickup truck front hubs bolt into the van knuckles and preserve the 8x6.5" hub bolt circle that the 2006 van already has.
   3. The 2011+ axles have 36 spline outer CVs that only work with the 8x180mm front hubs from 2011+ trucks.
      I'm not sure what year the vans went to 8x180mm, but for vans built with the 8x180mm pattern, using the 2011+ truck axles and hubs would be the sensible course of action.
   4. For 8x6.5" vans, maybe custom axle bars to fit the 2010- inner CVs and 2011+ outer CVs would be the most direct method.
5. If you've made it this far, you should be able to figure out the transmission and transfer case of your choice.

[ericjon262]

I feel like transfer case and transmission are probably by far the easiest part of the swap. it would be super handy to have a donor van to measure everything off of for the engine crossmember and differential mount without having to take yours apart...

[The Dark Side of Will]

I can rework the diesel fuel pallet and switch over to torsion bars with the only permanent mods being the mounting tabs welded to the inner faces of the frame rails... and even just leave the van like that for the rest of its service life.

However, once I start cutting to fit the diff, I need either to finish the job or do a lot of welding if I run into a big enough road block.

I think the big unknown right now is whether I need to do something with the left engine mount tower. Quigley didn't, but having seen the way their junk is hacked together, that doesn't mean much.

[ericjon262]

Maybe we discussed it already, but what about swapping in a truck K member? are the frames that different up there? GM usually tries to minimize variations across product lines.

[The Dark Side of Will]

I can take a look at how the truck front suspension crossmember is put together, but I'm 99.99% sure on a year by year basis, trucks and vans are completely different. For example, the engine is FIVE inches further back from the front axle in the vans than it is in the trucks (weight distribution, j0!1!)

However, since the GMT600 van was first produced in 1996, has not had a major update since, and 2006 truck control arms still fit... Maybe I should look at how a GMT400 truck is put together in the front end. Actually... a friend of mine owns a half ton 4WD Tahoe of that vintage, so I can crawl under that for a peek.
Interdasting.

[ericjon262]

it's worth a look with a tape measure, it could save weeks of work if it works...

[The Dark Side of Will]

Well...

Good photos of a GMT400 4WD body-off build here: https://www.gmt400.com/posts/952816/

The rear pivot of the LCA's is similar-ish to the vans. I haven't found a photo showing a bolt in crossmember between those two pivots, so I'm not sure the chassis has one. If it does, then that bolt-in crossmember might indeed be a shortcut vs. building a new bolt-in crossmember.

The LCA rear pivot pickup points are welded to the frame and are not the same stampings as the vans use.

Also, the pickup trucks have frame kickups to hop over the axles while the vans do not. The van frames are flat in that area. A modest lift of 1-2" appears to be a requirement just to get the axle shafts level.

[ericjon262]

bummer, I was hoping there might be a simpler solution than fabricating something more or less from scratch.

[The Dark Side of Will]

bummer, I was hoping there might be a simpler solution than fabricating something more or less from scratch.

ETA:

I think the big unknown right now is whether I need to do something with the left engine mount tower. Quigley didn't, but having seen the way their junk is hacked together, that doesn't mean much.

Moving the engine mount tower baseplate further up the stamping would be a tougher packaging/design/fabrication challenge than piecing a crossmember together from scrap metal.

[The Dark Side of Will]

The GMT400's use a clamshell version of the 9.25 front diff that has a lot of "junk" on the outside. In addition to the width of the case half flange increasing the size of the diff in the wrong direction, the bushing bosses and stuff that work in the GMT400 and GMT800 are all in the wrong places to work in the GMT600/610.
The 2011+ diff uses more subtle mount bosses on the diff case plus spreader bars for the mount bushings. Building GMT610-specific spreader bars that mount below the diff looks like the best way to get it into limited space.
That being said, the potential utility of re-using a GMT400 crossmember, @$$uming it exists, incorporating the earlier style diff mount under the pinion, is diminished.

ETA: Also, the steering linkage on the 600's/610's appears to be identical to the steering linkage on the GMT400's, at least the 4WD GMT400's.

[The Dark Side of Will]

I feel like transfer case and transmission are probably by far the easiest part of the swap. it would be super handy to have a donor van to measure everything off of for the engine crossmember and differential mount without having to take yours apart...

I need to go to the local friendly junkyard for a look, but I might be able to snag a frame or cutoff for purposes of fitting the diff. Interdasting.
There's nothing to worry about for body clearance. I only need to deal with the frame.

I have everything else figured out, I think. I think at least the torsion bar conversion is straightforward (famous last words). Repackaging the diesel fuel pallet is going to be a pain, but I have it ~2/3 figured out. I can move the fuel cooler in front of the radiator next to the aux transmission cooler. A knowledgeable user on DieselPlace recommends the B&M 70274 unit.

https://www.dieselplace.com/threads/upg ... st-9902587
https://www.summitracing.com/parts/bmm-70274

I can replace the rotary priming pump with a solenoid lift pump that my dad found for a family member who bought a DMAX GMT 800 a few years ago.
From there I just have to relocate the filter such that it's both out of the way of the driveshaft and torsion bar, but also the last thing the fuel sees before it goes into the CP3 HPP.

[The Dark Side of Will]

I feel like transfer case and transmission are probably by far the easiest part of the swap. it would be super handy to have a donor van to measure everything off of for the engine crossmember and differential mount without having to take yours apart...

I need to go to the local friendly junkyard for a look, but I might be able to snag a frame or cutoff for purposes of fitting the diff. Interdasting.
There's nothing to worry about for body clearance. I only need to deal with the frame.

In thinking about this a little more... The diff's position is basically pre-determined. I needs to be centered left/right between the frame rails. It needs to be high enough that the inner CV joints just barely clear the frame rails and it needs to be positioned fore/aft so that it just barely clears the swing of the steering linkage. There isn't space to put it anywhere else. If I can get it to fit there on a chunk of a van frame, then it'll go right into the actual van, with the same cutting. I might be able to get the most difficult part of the job done first!

[ericjon262]

yeah, I think getting van frame horns is really the best way to do this, probably even better if you can get from the bumper to trans crossmember to help keep it lined up and square.

[The Dark Side of Will]

There's a welded crossmember ahead of the engine which carries the steering linkage... that should be pretty good. The trans crossmember just bolts in, but including it would help.

[ericjon262]

There's a welded crossmember ahead of the engine which carries the steering linkage... that should be pretty good. The trans crossmember just bolts in, but including it would help.

I just saw a picture of a van frame, looks pretty beefy up there, fully boxed and everything, Probably wouldn't need the crossmember.

[ericjon262]

on one of Richard Holdener's videos, he was walking through the junkyard looking for engines, it was a pretty boring video, but it brought something to light, apparently lots of wrecking yards cut the front of van frames off to ease removal of the engine, might be a viable way to get a mock up frame section.

[The Dark Side of Will]

There's a yard that www.car-parts.com says has the front frame section of a van that's pretty close to being on the way to Promar for me... I'll give them a ring next week and grab the frame section on the way.

I grabbed some wheels for my Benz right next door to them when I dropped the block off with Promar back in November.

[The Dark Side of Will]

There's a yard that www.car-parts.com says has the front frame section of a van that's pretty close to being on the way to Promar for me... I'll give them a ring next week and grab the frame section on the way.

I grabbed some wheels for my Benz right next door to them when I dropped the block off with Promar back in November.

Ooops... these guys don't have it anymore. Looking more towards Pittsburgh to pick one up in my price range, which means that'll be a dedicated day.

[The Dark Side of Will]

I found this on a Facebook advert:



This is a 1500 AWD van, but I need to check the parts lookup to see if I can find the crossmember, as that could either just be used or serve as a starting point for a crossmember that would work. Note that the rear diff bushings on both L and R sides sit on top of that crossmember.

I see that the control arm pivot boxes hang down lower than the RWD ones do, so that would have to be dealt with in order to use this part... neither super east nor bolt-in. But nothing fun is bolt-in.

I also just noticed that the rear/lower diff mounts sit on this crossmember. I guess the forward/upper diff mounts bolt to brackets on the frame?

Also, the 1500 AWD vans have rack/pinion steering. I need to look at the crossmember to see if the rack might work in the 2500/3500 vans and improve diff clearance vs the drag link.