Technical Ladder bar for open driveshaft conversion

Hello guys, recently I've been researching, and i may have found a third member to convert up to '54 Chevys from torque tube to open driveshaft (If it works out i'll do a thread on that).

Anyway, those axle use a pivoting mount instead of a spring pad, so without the torque tube i'll need a way to keep the axle in position, and the logical option is a ladder bar, but how do i build one?

What design considerations i should have? Should it be parallel to the ground or to the driveshaft? To neither one (triangulated)? About how long should it be?

I did a quick sketch, with no concern for dimension or angles, just to illustrate the idea:


Edit: While doing further research, I've found out that this is called a floating axle housing. and what i need to locate it are not Torque arms, but Ladder Bars! (I changed the title for clarification)

 

Don't over think it, leaf springs and ubolts have done fine, Look at 55+ years of your Chevy.

Now if you're drag racing...

 

You only need to remove pivot. Next drill new holes on spring pads of replacement rear so axle will sit centered in wheel opening.

 

I know the simplest way is making new spring pads and mounting the axle with u-bolts.
The thing is: I would only be changing the differential/third member, not the entire axle, and i didn't want to mess with the mounts already in place (which have already been moved years ago to work on the '28 frame i'm using).

 

I would make a bracket to bolt onto the third member with “ears” to attach a ladder bar as close to the driveshaft as practical. Then build a single ladder bar that attaches to those ears and to the chassis exactly in line with the center of the front u-joint. It won’t be geometrically perfect in all respects but it might do what you need it to do without binding.


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The OP's axle uses a pivoting mount instead of a spring pad.

 

When I read the post I made a poor assumption he was changing out the entire rearend for another.

 

Wasn't poor. There was no mention it was in a 28 frame in the opening post.

 

Sorry for the confusion guys. I should have mentioned what the axle was mounted into. I did however say that i found a third member, and not a rear end, so in my view it was implicit that i was not changing the axle.

 

Instead of a solid pivot point as you have drawn. Go with a slider system (works like close drive shaft tube). Google 82-02 Trans Am Torque Arm. For now look at this.

 

If you mount the axle on a pivot mounted on the leaf spring it will move backwards when going over a bump or just adding weight in the back of the car, the torque arm mount on the axle will move forward with the same action causing a fluctuation in the pinion angle. JW

 

How about something like this?!
6sally6

 

Use "Truck Arms"

The greatest force on them is
1: "forward thrust" to propel the vehicle. [this force is from the outside driving wheels]
2: rotational "downward torque" from braking.
3: pinion torque reaction.

in ^^ that order

 

I assume that what you have drawn in the first sketch is what you have now, except with a closed torque tube. This must have a slip tube, or the present suspension would not work without binding. I also assume the "axle pivot point" is of singular articulation and can transmit the acceleration/braking thrust through the springs to the chassis (i.e., it is not like a shackle),

Also, I assume the "ladder bar" you are proposing is not truly such, in that it, on it's own, does not prevent the axle housing from rotating, i.e., it is pivoted on top of the center section. So, what you are proposing is functionally a "four bar linkage" setup, with no consideration given to making the upper and lower arms of equal length, or parallel to each other, or to the ground. (The front halves of the springs are essentially the "lower links", and the single upper link correctly serves as replacement for both upper links.) Note that with an open drive shaft with a slip joint, there is absolutely no reason to extend the "ladder bar" to a location in close proximity to the front u-joint.

The geometry would be better if the front portion of the spring were longer, parallel to the ground, and the upper link shortened. But I don't like the longer leaf being in compression under acceleration, and the upper link, being quite long, would need to be pretty robust to preclude buckling under heavy braking.

I think I agree with Johnny Gee that his suggestion would be the easiest way out. Note that the axle end of the slider tube would need to be affixed to the center section, in a way that would preclude axle housing rotation about its center line, but allow very slight rotation around its vertical axis.

Or just go to a standard parallel leaf spring system.

All of which begs the question, why are you doing this in the first place?

By the way, if you had told me the car is powered by a Model A banger or a V8-60, I may have had a different response!

 

Here's how I did my '53 Chevy PU. Made riser blocks to compensate for removal of the factory swivel from I think 1.5"x5" rectangular tubing, had new U-bolts made at my spring shop. Drill hole in bottom of blocks to clear spring bolt, index axle. Most medium size towns have a spring shop to service big trucks. Weld the blocks to the axle.

 

I put ladder bars on my leaf spring Willys, they have a slip joint in front mount made from MII front end rubber donuts.

 

I think maybe a similar to a cal trac might be simple and easy to do also

 

Both really great ways of turning the entire rear axle housing, along with the bars, into one giant rear anti-sway-bar.

Might be fine for a drag car, but could make for some undesired handling characteristics on the street.

Who wants a car that cannot corner, at-speed, for fear of massive over-steer?

There is a reason why Chevy (and NASCAR) truck-arms, and Pete & Jakes ladder bars get closer together as they go forward, ending just a few inches from each other, at the front.

 

Hamber @GraeffSS, I don't have any knowledge to add here but good to see you hanging around and wrenching with the old stuff...Lots of Thinking Hambers here with knowledge to admire and glean...thanks everyone...I get most of what you and the others saying...parallel leafs and a pivoting rear end And Torque Tube...lots going on there...

 

If the rearend is already on pivots you should look into a torque arm as mentioned above ala the 1982-1995? GM F-body rear suspension.

 

I get what you're saying, i'll take it into account

I'll keep the "Truck arm" option in mind, in case a ladder bar doesn't work

(Responses for this one in red within the quote)

I got this part that for a drag car, the bars can be parallel but not for the street.
Since mine would be just street driven, my idea was putting just one bar, as close to the center as possible to avoid the "sway bar axle effect"

Thanks, so far this seems like the best solution. I'll look into how the slider is built

From your ideas i came up with a new sketch:

The top bar would be adjustable (for setting the pinion angle), and the ends would be Heim joints.
The bottom bar would have the slider on the frame attaching side, and the length/attaching point would be decided latter (I'm reading about instant center and what it influences).
(Note: I drew the top arm that short because i believe it may hit a frame crossmember if made longer)

 

This is all a lot of work, to avoid getting/making static spring perches, and some u-bolts.

 

Truck Arms are ladder bars [ except they point together at the front as an "A" frame ]

Could you give us some more details about the original leaf spring pad/pivots.
Are they floating [shackle style] or do they swivel only.

The leaf spring and the torque tube both move different arcs, so unless one is floating it will bind.
Does the original torque tube have a slider type driveshaft?

He could simple add traction over ride bars like Shelby Mustangs had [pseudo 4-link]

 

They only swivel, and the original torque tube was a slider type

I looked it up, it's an interesting option, i never knew Shelbys were that way.

I discussed the options with my father, and in the end i think we'll go with new perches and U-bolts...
Can't blame me for wanting to do something different though...

 

This is very common on Rally Cars [Leaf Link Suspension] because FIA rules required the original supension but traction devices were allowed.

Ford Cortina GT's [Mk1] had traction override bars from the factory
[In the attachment the upper is Lotus Cortina and lower is Cortina GT]

 

The '82-?? F bodies used a torque arm from rearend to transmission. Also a panhard bar behind the axle and lower control arms as well. Might be a bit messier than you were thinking? It's a good compromise between acceleration and handling though.

You could find what it looks like exactly on thirdgen.org.

 

^^^^^ A leaf spring suspension does not need panhard bar.

 

Mimilan Yes Chev torque tube has a slip joint at front of enclosed driveshaft. Geg

 

Yes. Offered in case thread starter wanted "the look" of ladder bars. Surprisingly handling with the setups is really pretty good. Easiest solution for his truck is the previous suggestion I posted.

 

The truck arms have two things that allow them to work so well. First is they angle in and the front ends are relatively close together. Second is the GM arms are I-beam profile, which allows them to twist, therefore negating a lot of the anti rollbar aspects. If the arms are tubing, they have way higher twist resistance.

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