Technical COE rear suspension advice

I'm planning a build on a '52 Ford F6 COE using the original chassis and need some advice on the rear suspension.

I'm planning to use it as a hauler and I need to be able to lower the rear end. I'll use a Jag IFS up front.

For all sorts of reasons I won't bore you with (mainly regarding UK identity regulations), I need to use the original chassis and can't modify it in any way. Any additions can only be bolt on. The front is no problem as the Jag IFS can be made to bolt in on it's rubber cushions after a little clearance tweek here and there.

My question regards what to do with the rear end. I have the two chassis rails which I can't alter and that's it - a blank canvas.

The stock leaf spring and rear axle has to go as it's heavy and over rated for the max 7,000 lbs I'll be running at.

So, I could fit a 9" and go with a 4 bar system? I've discounted ladder bars for the street.

Or do I look at an IRS system (maybe Jag?) to allow me to go much lower?

As I can't C notch or in any way touch or modify the frame rails, I feel I'm very limited in how low I'll be able to run the rear - even it I go down to 30" tires.

I can make large bolt in mini subframe mounts that bolt up inside the frame rails so a bolt in system holds no fear.

So, with a blank sheet of paper but with straight stock rails - what rear end would you fit to give decent ride height flexibility, roll articulation and a decent ride?

A side question about 4 bars.... I get all bitter and twisted (pardon the pun) over binding issues on triangulated systems in articulation and have read the long thread on here about this topic with interest. A ompletely parallel 4 bar with a watts linkage seems to solve most of those concerns.

On a low speed, low power, car hauler, do I need to be concerned with anti squat or instant centre positions, as the way I see it, a completely parallel 4 bar system won't have an instant centre as the bars will never meet if they continued forwards totally parallel. However, the pinion angle will always be correct and parallel with the tranny output and with narrow rubber bushes, bind in roll will be absolutely minimal.

This is my first build of this nature so I welcome input from those experienced in such matters.

To refresh, the criteria. must follow:

1) Frame rails stock and un-modified.
2) Decent amount of lowering required
3) System must be bolt in.
4) Street driven on bendy, cambered, bumpy UK roads with lots of roll articulation without bind required.
5) Truck will have low power at no more than 250bhp.

Thanks in advance.

 

IRS and coil overs were not designed for heavy towing. Leaf springs would be better with a 9" and sway bar IMHO. Use auxiliary airbags on top of leaf springs for heavy towing. A 31 spline rear of an 8.8" Explorer would be stronger as axles are heavier.
We have similar strict regulations down here so I feel the pain.

 

Just for clarity, the entire vehicle with the (very light weight) race car on the back will weigh no more than 7,500 lbs so it won't be heavy. The entire race car and deck will weigh approx 1 ton.

I don't want to use leaf springs as they are heavy and ugly (IMO) and will limit the amount of suspension adjustment I have, as I want to run airbags to drop the frame as low as I can for loading and un-loading. The rear deck will be removable so I can drive round the rest of the time with a naked chassis on show which still needs to give a decent ride and not sit too high without the deck and race car - hence the desire for air ride so I can adjust the hight and spring rate to suit the load changes.

If IRS is not a good solution - what are the thoughts on totally parallel 4 bar with a watts linkage to avoid binding.

 

A parallel four bar with watts linkage should work fine. Since you are not drag racing, the instant center is not really an issue. You could build the bars to have an instant center way out around the front axle, and have minimal pinion angle changes while driving. The extreme lowered position would be sitting on bump stops and not really used for driving on the road.

As for what rearend to use? I would go solid axle not IRS. Much easier to construct the mounts and bars. Airbag is good idea for adjustability and ride stiffness when loaded vs unloaded. Just my opinion, but a dually style rear would be more aesthetic, and provide more than sufficient safety factor. Most US dually rearend are all full floater style which is also better for loading the bearings through the hub vs through the axle. Some adapaters for the front and you could run the same dually offset wheel front and rear, plus make the bolt pattern same for each. You could also source a 73-91(?) GM 1-ton fornt suspension, they unbolt form the frame and then bolt that into your COE frame. It would give you the certainly heavy duty IFS, and match the rearend potentially. I have airbag on my COE, which uses 74 GM IFS (and chassis for that matter!).

 

It seems your major limiting factor will be the axle hitting the frame, which I am assuming is two straight beams. If maximum suspension travel (adjustability) is what you are going for, you could go with a "cantilever" style with an airbag. Some mini-trucks use systems like this to get a decent ride height but then drop it on the ground at a show.

I saw a car that had a 4 link style setup, but had perpendicularly mounted torsion bars that acted as the spring, but at the opposite end of the bar from the link they had a cam and follower, driven by an electric motor. So the "spring" was the torsion bar, but how "twisted" it was (which controlled ride height) was controlled by the electric motor(or hydraulic ram)

It's going to take some thinking, but perhaps a combination of squatting the suspension as much as possible, with a tilting bed, you should be able to get what you want!

 

Leaf springs are ugly? BAGS are hideous looking.

You seem to be all over the page, can't have it real low without notching the frame. Why is triangulated 4 link always the go to? Use a truck arm setup like the Chevy trucks used as well as Nascar, pivots close together in the front and clamped to the rear with U bolts. Those rubber things that hold air just in front of the axle.

I made a large wishbone for an OT ride out of 1/4 wall 2x3 tube, cut and tapered it from the axle to the front single mount, 1 1/4 shank heim joint with a 1 inch cross bolt. This set up with a spring needs no lateral locator, the rubber things will need a lateral locator of your choice.

 

This has nothing to do with traditional hot rods/cutoms. COE/Step Van/Milk Truck/1-Ton (+) builds need to go on the social forums;

http://www.jalopyjournal.com/forum/social-forums/step-vans-coes-1-ton-trucks.851/
http://www.jalopyjournal.com/forum/social-forums/coes-cab-over-engine.283/