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Converting Torsion Bars to use as sway bar

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Converting Torsion Bars to use as sway bar

Postby davidvdm » 29 Oct 2015 09:49

Morning all, as you all know I have the Sani with MQ Patrol SFA and suspension conversion. Now I have ended up with a 7" lift and one of my projects is to install a sway bar.

I have a fairly wobbly ride, and the COG is now so much higher that cornering is an interesting experience.

As you probably also know, I build stuff on ZERO budget and from scrap I find laying around.

So here is the question.... Would a torsion bar be too stiff to use as a sway bar?

Another question would be if a torsion bar is designed to only take tension in one direction?

I have an idea to cut the left and right torsion bars and join in the centre.

Three main reasons would be:

1) Standard torsion bar is too long to be used as is. So to save and use the splines on each end, it would be best to cut the centre portion out to shorten.

2) As torsions are clearly marked for left and right, I have the feeling that they only take load in one direction. This would mean that I would need to use portion of each torsion bar to accomplish even load carry in both directions as required by a sway bar.

3) The centre joining point of the two torsions can fairly easily be made to be a disconnect. This would save me from figuring if the two ends can be welded or how to join them together.

The idea is to have a simple hex cut onto the end of each portion where they meet in the middle. The one side would be cut deeper than the other. A long 25-26mm socket can then be slipped over the two ends and by moving it, it will engage the two ends or disengage the one section from the other.

A simple sleeve would keep the two ends lined up no matter in which position the socket may find itself.

Should be easy enough to lock the socket in either the open or closed position.

The Jeeps have the Anti Rock system that I base the idea on, and I presume that the length of the arms can be used to compensate for a bar that is too stiff. But then you also don't want the flex to happen in the arms, but rather on the bar it self.

Simplest way I can think of to make a very tight sway bar with a easy disconnect as an added prize.

Other advantage is that using what I have, I am probably going to need about R100 worth of bits and pieces to do this job.

My one brother in law is a fitter and turner, boiler maker and welder, and tells me he can do the hex cutting on the joint easy.

If I can do this, the original sway bar that was on the front of the Sani can be employed in the rear, but the disconnect would be a pain.

Peter, I know you will be able to give me some advise on this one. So lets hear how good or stoopid I am in my thinking.
David - Bfreesani
1997 Nissan Sani MK3 2.7TD - Hillbilly (SAFANI)
MQ Patrol C200 SFA
MQ Patrol H260 LSD Rear
MQ Patrol Transfer as second low range
5" Lift
33"x12.5x15" tires on 8.5J rims
DIY rock sliders
DIY Snorkel
Madman EMS
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Re: Converting Torsion Bars to use as sway bar

Postby Peter Connan » 29 Oct 2015 17:44

It's a nice idea, but I think in practise it's going to give you a hiding.

The stiffness can be "set" by getting the length of the lever arms at the ends right. But how to calculate how much effect you want is going to be very tricky.

Torsion bars can flex both ways, but used ones tend to break if used in the opposite direction to what they are used to.

The issue will be your joiner setup. If you look at the standard torsion bars, you will see that the ends are bigger to allow for the splines to be cut. If you cut the bar, you don't have that, and in fact once you cut the hex in, you will have even less material. This will cause huge stresses in that area, instead of taking the stress over the whole length of the bar. And therefore, all the twisting will happen right here, and it WILL fail, unless you make it so stiff that the body can't roll at all in corners, which will give you allsorts of other issues.

Sorry, but unless you can find two torsion bars that are the right length, without having to cut off one of the upset ends, I would not recommend.
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Re: Converting Torsion Bars to use as sway bar

Postby Peter Connan » 29 Oct 2015 18:53

So here's another idea you may be able to find enough scrap iron to do:

A largish thick-wall pipe mounted across the chassis, with slots cut across the ends and holes drilled at 90 degrees to the slots.
A leaf spring cut split in two, with holes drilled in each end, mounted in these slots.
Short tie rods between the "loose" ends and the axle.

The big disadvantage of this is that it will be more difficult to fit disconnects to, and that the pipe will have to have very thick walls or some re-enforcement.

The biggest advantage is that it will be easy to "fine tune". If it's too stiff, grind the blades narrower, if it's not stiff enough, grind them shorter.
Mag ons ons kenniskry met lekkerkry aanhoukry.
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Peter Connan
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Re: Converting Torsion Bars to use as sway bar

Postby davidvdm » 29 Oct 2015 21:09

Spoke to my BIL about this. Now what we don't know is how much stress is going to be on that sway bar compared to the forces it worked under as a torsion bar.

My feeling is that it could be less, but I could be mistaken. His alternative is to weld a nut onto the ends to rather enlarge the "disconnect" to something like 32-36mm. He tells me he can temper the steel again.
David - Bfreesani
1997 Nissan Sani MK3 2.7TD - Hillbilly (SAFANI)
MQ Patrol C200 SFA
MQ Patrol H260 LSD Rear
MQ Patrol Transfer as second low range
5" Lift
33"x12.5x15" tires on 8.5J rims
DIY rock sliders
DIY Snorkel
Madman EMS
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davidvdm
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Posts: 372
Joined: 13 Sep 2011 15:47
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Full Name: David vd Merwe
Nickname: David - Hillbilly
Home Town: Carletonville
Current 4x4: 1997 2.7TD Nissan Sani Mk3 4x4 SFA (SAFANI)
Home Language: English/Afrikaans


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