Turning something into a dually... maybe

Stick with me here.  I figure you guys are just crazy enough that you might like this.

I have a 66 Bonneville that has now become a 30-year long project.  The first few years or the project in it's condensed version went like this:

• Decided to set it up to tow our camper of 6800 lbs when we got married.  I figured that was probably not too much more than what someone would have towed with it back in the 60s using one of those chains around the bumper.
• Started looking for a 12-bolt to replace the 10-bolt.  Awesome dude at the junkyard disappeared on a forklift and came back with a 10.5" FF 14 bolt.  He said "measure that."  It was darn near perfect.
• That meant I ditched the idea of using later B-body 11" discs for the front, and instead swapped in front knuckles, brakes, and stuff from a 78 3/4 ton.  Bingo.  I now have an 8-lug Bonneville.
• I really wanted a diesel to save a bit on fuel expenses, but the only option that had a chance of fitting under the hood was a 6.5TD, and later when the Dmax came out, I didn't have a prayer of affording one.  I ended up building a Caddy 500 with some head work and a smaller-than-stock cam.  It really did well, but I never got it fully sorted and it sat forever.

Skip ahead to today.  I'm now at a point where I can likely afford a Dmax to drop in, but I also love overkill, so I was thinking about making it a dually... but not with a wider rear track.  Narrow the snot out of a dually axle, narrow the frame, and use fat-ass tubs in the trunk.  I don't mind a little bit of widening... like if the rear had something like 4" flares, I'd be ok, but I don't want to graft on full fender buckets from an F350.

We had an early 70s F250 that we did this to at the old shop where I used to fab.  The body was bone stock fleetside, but in the bed it had 2' wide tubs.  Underneath was a narrowed Sterling dually axle.  I wasn't around when they narrowed the frame, but I recall we just mounted the leaf springs and shock mounts further inboard and started driving it.

How does one begin to come up with a logical/suitable suspension setup?  It will be a clean slate, so I don't have to keep the trailing arm setup it has now.   When you have something like coils or leafs that are right near the kingpin axis, that's one thing, but we're talking about moving suspension components inboard by a foot or so and I can't imagine how to make it work well.  Emphasis will be on weight handling and not being a total bear to drive.  I'm not talking about towing 15k, but I'd like to give 7000 a shot.  I want to roll into the challenge towing a 24' enclosed trailer with this thing and have you guys just be like "SMH, that guy is crazy."

Nothing will change about the up/down weight on the springs, so that's simple.  Body roll will be amplified since the longer lever of the axle (and body weight) having more leverage on the spring rate... is that just solved with bigger sway bars?  I know drag cars do this sort of thing all the time, but they only go in a straight line, and shifting the body and weight transfer can be used as a benefit.

So help me spitball some math/logic on this.  I might scrap the whole idea, but it might be pretty neat to have a dually rat rod 66 Bonneville with a Dmax and a ZF6 and clearance lights on the roof.

Could you make it a bit less narrow and use super singles?

Why narrow when a cab and chassis diff will probably fit. My 76 c30 dually dump truck rear was narrow

That's true.  i might be able to find one the right width.  I was kind of thinking that the 14 bolt I have is already here, already a posi, and narrowing isn't a terrible thing.

Aside from owning a couple dually trucks, I never did much about researching what's what.  I do know that many times when truck manufacturers get to the 1-ton and up, class 2 through 5 trucks, they use pretty much cookie cutter AAM axles.

What about using a 4-link with panhard and air bags to get the springs as close to the wheels as you can while having some adjustability?

The spring you want when you have tongue weight will make the car awful to ride in when you're not loaded. 

ShawnG said:

Could you make it a bit less narrow and use super singles?

Yes, at the risk of not being able to transport a spare.  Having a dually with 6 identical wheels and tires is kind of like having a functioning spare.  I can also buy six 215/75-16 E-range tires for the cost of one super single.  Granted, the SS will likely out live the rest of the car, so there's that.

In reply to ShawnG :

Air is a definite want.... to the point of wanting air brakes as well just for the awesomeness of it.  Air bags will be used - either as a full suspension, or as an assist for when a load is on.

But air brakes.... that's a different thread.

It's almost like I need to find a totaled Top Kick or Kodiak and steal/modify all the parts.

When you say '66 Bonneville, just to be clear, we're talking about a Pontiac Sedan, right? Is that car body on frame? And if so could you just bolt the body to a modified truck frame? Is that not as much fun? 

I mean:

As I recall cab and chassis rear ends are about 6" narrower than pickup truck dually rear ends.  That would get you about half of the distance you need, the rest could likely be made up with flares. 

93gsxturbo said:

As I recall cab and chassis rear ends are about 6" narrower than pickup truck dually rear ends.  That would get you about half of the distance you need, the rest could likely be made up with flares. 

Box flares, for awesomeness....

dannyp84 said:

When you say '66 Bonneville, just to be clear, we're talking about a Pontiac Sedan, right? Is that car body on frame? And if so could you just bolt the body to a modified truck frame? Is that not as much fun? 

Yes.  Not a Triumph motorcycle, although I am just insane enough that a dually bike would be something I might attempt.

It is body-on-frame.  I will look into putting it on a truck frame.  I kind of dismissed it because many truck frames are remarkably straight/ladder-like.  It would still require narrowing the frame to fit the duallys inside the body.

For reference:

In reply to Duke :

Yes a crazy-hard rear sway bar can work to address the decreased roll stiffness on the rear axle. You could even use pushrods and bellcranks to change the motion ratio between the suspension and the bar to effectively stiffen it further, a lot of race cars with bellcrank suspension do this.

This is how it's set up right now.  I want it to ride about this height (or lower) and tuck all that dually goodness under the rear.

This seems kind of insane.

I like it

Commenting to eventually see the video of C Mitt arriving at the challenge pulling a trailer behind a dually Bonneville, with the sweet diesel sound. Go man go. 

In reply to OHSCrifle :

Haaa!  I hope it doesn't take me another 30 years.

When I do it, I'll have a dash cam so I can record all of you dropping your beverages.

In reply to Curtis73 (Forum Supporter) :

Come to think of it, I'd rather see it in person. Life goals. 

In reply to Curtis73 (Forum Supporter) :

Could do it with a chase cam:

Two thoughts, just thinking out loud:

1) Extend the trailing arms so the airbags are behind the axle. The arms can be angled or bent to move the airbags out further from the centerline. Shocks could also be moved further out to help with roll. 
 

2) Alternative to the dally, what about a hidden tag axle with 13-14" wheels for added stability and tongue weight capacity. I know we've seen photos of one before, but I think it could be done cleaner and more subtle than that. Maybe fold in rather than up, with air ride and some over lift there could be enough clearance.

edit: added some pictures for visual of concept

In reply to No Time :

That design also effectively makes the axle into one really stiff sway bar, and depending on how it attaches to the frame, may eliminate the need for a panhard.  May need a CV joint or at least a double cardan.  Lots of angle change at the pinion.

After seeing a dually today with single wheels on each side with hardly any sidewalls. This would be da bomb to me for this.

This  is what was on the dually I saw.

In reply to MyMiatas :

I love that look.  Here is my GRM Pinterest inspiration photo album.  This kinda thing, but under a Bonneville.

So are you gonna tub it in the rear then?

So you can keep the tires inside the body