[MGNZ]

Has anyone ever tried a simple dyneema limiting strap mounted on top of an axle A-Frame to control axle wrap? seems like a simple option without having to worry about articulation geometry, twist etc. etc. the commercially made traction bars seem a bit OTT for a little zook.

[Gwagensteve]

Yes, in fact when Gregc and I were building his car, we looked into building a conventional traction bar. The Engineer we were using put the question back to us and said " work out the axle path and determine whether you can use a traction bar without binding the springs" .... the answer was, we couldn't.

So we made mounts up to use a cable. We've never made or fitted the cable as we never found it necessary, but the provision is there.

Yes, it could be made to work, however, I think it's a poor application for dyneema. A steel cable with a turnbuckle at one end would be better, as the tension would need to be tuned a little to get the characteristics required.

However, consider this: Any load that goes into the traction bar if it's a single point bar above the diff, will just see that force put into the leaf springs. A horizontal bar or cable working in tension isn't really opposing the force in the most efficient direction.

Cars with aggressively effective traction bars can bend springs up near the spring hanger, lock the suspension movement out, or "jack" under power

If the leaves have arch in them, more force restrained by the traction bar will try and shorten the spring up (i.e increase spring arch)

I'm not advocating against a cable, I'm just outlining that it doesn't work like the photo of the bar you posted, which does actually fight the rotational force occurring with a very long lever. The length of the "lever" in the case of the cable, is the height of the bracket above the diff - significantly shorter than the length of the bar in the photo above.

Steve.

[jdk81]

You have to consider loading.
Just one wire at the top, means that the leaves are in compression, and will buckle easily.
This is why spoa cars can just run a solid link on the bottom of the diff.
Leaves go in tension, and solid bar is in compression.

SPUA do much better with a system like the one above (yes i know its on a SPOA).

I run hilux ifs leaves from 2008 hilux.
They are really long and being used back to front to get the axle where i want it and not have a hell of a lot of leaf behind the axle.
I get stupid axle wrap.

I tried cable, in a triangular sytem a combination of both above and it sucked. Was very slappy. Huge shock loading.
I drove it out of the shed, around the yard and back into the shed.

I tried a damper and cable solution, to resist the speed of the loading on the cable and it sucked.
However, it sucked a lot less than the cable.
I ran this for 8000km maybe.

I have now given up on totally avoiding loading the springs, and modified it.
I used an old tie rod to set it and leave it. It has very little loading on the springs.
Build is similar to the one above.

[just_cruizin]

So simply, you need to stop the diff rotation. The cable will stop the top pulling back but you also need to stop the bottom going forward and springs won't do this

[MGNZ]

Thanks for the suggestions. It sounds like the compressive forces on the front of the leaf pack during wrap are much greater than I thought they were. Will finish my T-case gearing changes and take it out for a drive with a gopro under and see how bad it really is. I have just softened the rear leaf pack to get more flex and the shocks were already dented from wrap so think it's gonna be bad. Mark

[alien]

Build a caltracs style setup - it's still straight forward and works great.

[Gwagensteve]

I still can't recommend caltracs until someone works out how to run them backwards so they sit above the axle. The ground clearance lost is too significant in our terrain.

I know they work for you Alien but our local terrain would turn them into anchors.

[alien]

Fair point.

Mine don't hang any lower than the factory leaves though, and they're more 'streamlined' than the stock u-bolt plates. So for SPOA application there's not a significant difference in clearance.

I do bash mine on occasion though!

[Gwagensteve]

As a SPUA there's junk under the u bolt plate and junk under the spring at the chassis end. Both are anchors in stock form, let alone with stuff under them.

Our cars have hashed spring hangers and body mounts. Caltracs would be a nightmare.

[Spokerider]

Yes, it's an old thread, but with good info.......so I'll keep it going.

Has anyone used a limiting strap as an anti-wrap device? Thinking about it, and looking at it, it should allow full rear axle rotation from side to side and allow full rear suspension compression.

If I were to make this.......how much "slack" would one want in the strap, with car sitting at rest?

Here is a link to a traction bar that a guy make for his samurai. It looks like it works well.
https://www.youtube.com/watch?v=FHvaCAOzF_w

[Gwagensteve]

Yes, turns out this year Gregc finally fitted a limit strap to control wrap.

Yes, it was effective.

After it's first trip it needs to be adjusted up to take out the settling-in stretch.

I'd set it up so there was a teensy bit of tension on it static/at ride height, but that will depend a bit on suspension setup, Gregc's car basically sits very close to the bump stops at ride height.

You can see the strap working here.

[Gwagensteve]

I did skim through that Youtube clip.

Here's some comments: (I did just skim through it with the sound down, forgive me if it was presented as a trial and not intended for actual use)

A number of people locally have fitted traction bars to the factory chassis crossmember as per the video. They have always torn out, taking the crossmember with them. Likewise, I don't think there's anywhere near enough load distribution on the axlehousing.

I think there is excessive fore-aft movement in the shackle before wrap is limited. We were shown some moderate acceleration on a low traction, flat surface. stand the car on its tail and put some power in and I think all that shackle travel is going to make the back end hop.

To me, that setup has too many moving parts. The Sam's offroad style of traction bar (photo below) is well proven, and puts the shackle into tension under power, where it's most effective at limiting axle wrap. The application of the shackle in the video means it has to move a very long way before it's under tension. I've seen the Sam's off-road style work very well on a Samurai, but it was an extended wheelbase LWB that had a nice, long, flat bar. SWB cars are a challenge because the bar ends up short and relatively steeply inclined, which makes it harder to optimise the geometry and more prone to binding.



Additionally, how much traction bar you need is a function of how much traction you can generate and how low you want the spring rate. Something like Gregc's car above generates lots of traction on dry surfaces but has a low spring rate, so axle wrap is an issue. SPOA cars generate lots of axle wrap, but troubleshooting SPOA suspension is outside of the scope of this discussion.