[Beery]

So, my car gets axle wrap, and I don't want it to axle wrap (or at least limit it)

The rear diff is currently out of the car to get a bunch of other stuff done - full float, disk brake, fix the locker and new spring perches. I'm thinking while it's out I make an anti-wrap bar too. The transfer is also out of the car currently, so the crossmember I'd mount the shackle end to is also easy to get at, so it's kind of the perfect time to do it.

An anti-wrap bar seems to be an effective solution to me. I know a lot of Hilux guys swear by them, (I guess they also like triangle shocks and shackles the length of the wheelbase too though ) But they don't seem to be overly popular in sierra world. I haven't seen one in action (that I know of), or even know of anyone running one. Why is that?

From my research, this here seems to be the best design due to it not binding the suspension, or at least minimal:

(pics from rampt customs)




What's the downsides? I don't really know. Does the shackle type still bind the suspension? is it enough that its an issue? particularly on something like a sierra with minimal articulation.

I don't really know the do's/don'ts when building one. I found this:



I'm aware the mounts need to be strong. I've heard of housings being ripped open and crossmembers being ripped out. Does the top arm really need to be horizontal? I think the lower arm being horizontal on a sierra may package better.

Here's a coily radius arm thrown on the housing to get an idea of how it will sit in the car:



I plan to strengthen that crossmember that the body mounts are on and mount the shackle off of it. The wrap bar will be pretty close to the middle of the housing and should sit fairly flat.

I'm also aware Bogga had one in his LWB build here: viewtopic.php?f=4&t=48783&hilit=stretch+bogga&start=60

Very nicely done, and looks like it'd be a good thing, but the car was never completed, so no real world feedback.

[Beery]

Okay, so I've done some playing around to try get my head around it.

I clamped a bit of shs to the diff to simulate the wrap bar.

Here's ride height:



Here's full droop:



So that's roughly a 50mm change. It'd be a bit more, as I didn't fully compress the suspension. Obviously when the wrap bar is fixed to the shackle, this movement won't be able to occur. It's going to raise pinion angle slightly, and fight the leaves, turning them into an 'S' shape.

I don't actually think that's the end of the world though. I don't make a habit out of jumping my sierra, so both rear wheels are rarely going to be fully drooped out, except for very steep descents, or getting beached.

Because the wrap bar is mounted in the centre of the housing, when articulating, (one wheel compressed, one drooped) the centre of the housing will stay relatively neutral (compared to the the far ends) so this bind might not be much of a factor. I have seen wrap bars mounted on far ends of the housing (closer to the wheel) but after doing this little experiment, they would work that side leaf very hard in comparison to the other even when articulating, and only on one side. That might feel a bit funny. At least with a centre mount wrap bar, the bind will be the same on both sides.

You can also see a marker line on the shs. That indicates the forward and back movement when raising/lowering the car. It's only about 10-15mm, so it doesn't need much travel in the shackle.

If it wasn't clear, a Heim joint on the shackle end will allow for articulation, so I can't see how that would aspect be hindered.

Anyway, just some more thoughts.

[Gwagensteve]

My 2c


The Rampt Customs bar was originally developed by Sam Patton at Sam;s Offroad in Tulsa in the mid 90's. He had a very tall SPOA CJ with a pretty rowdy L98 from memory so axle wrap was a big issue.

As depicted in the photos though, the shackle is upside down - the load on the shackle should really be in tension, putting the crossmember under the shackle rather than over it. Set up in compression its more likely to put influence into the springs and under certain circumstances it might be possible to have the shackle "invert" which couldn't happen if it was in tension.

However, why fabricate all that stuff when the coil radius arm is perfect? build a shackle at the chassis end and the job is done.

As you've noticed though, any bar like this will put influence into the springs. It's unavoidable because leaves travel in an awkward path than can't be followed by an arm. when we were engineering Greg's car one million years ago, we asked about an antiwrap bar and the engineer said "if you can design something that won't put force back into the springs I'll engineer it". It was impossible, so we ultimately certed the car without the bar in it and installed a limit strap in place of the bar. This works just fine.
It's a trail gear limit strap with a clevis at one end to adjust it for stretch and preload.

[Beery]

Rampt (and I'm sure others) have done the bar with the shackle in both orientations. Why does it being in compression influence the springs more? isn't it just doing the same job. I can't imagine the shackle ever inverting. From my little test, there's going to be roughly 15mm of movement, more with bushing flex etc, but enough to get it to invert? I can't see that happening, so long as I set it up fairly vertical.

Yea, I got the coily radius arm out of storage as that's what I planned to use, however in typically coily fashion, it's bent. it's also missing bushes, and where I originally planned to put the shackle meant the radius arm was too long. Looking at it again though I could mount the shackle in front of the crossmember to suit the arm. (and a longer arm is better as I understand it, so win win) I may be able to straighten it, or a mate might have a spare. I did read wrap bars are more effective when solid mounted, (heim joints) as bushes can flex and allow axle wrap to start.

Gwagensteve wrote:

we ultimately certed the car without the bar in it and installed a limit strap in place of the bar. This works just fine.
It's a trail gear limit strap with a clevis at one end to adjust it for stretch and preload.

So, was a wrap bar built for the car originally? was it ever installed, or just went straight to the strap?

I like the strap for simplicity, but I feel the only time it can limit axle wrap is when it's got tension on it, so when that's happening isn't it basically the same thing as having a bar? it's still going to influence the springs. Although I guess it can pivot at the diff end. is it also only really effective at ride height? by rights the strap gets looser the more the suspension droops.

[Gwagensteve]

The compression thing is down to the geometry. There is a LOT of force on the shackle and if it's being pulled on its the force is only ever in a straight line from the shackle to the bar. however, when it's being pushed on it's going to want to try and compress and if the shackle isn't exactly at 90 degrees to the load on the bar it's going to try and fold flat as it's loaded. As it starts to do that it's going to push the bar fore/aft.

Yes, bars are more effective when theyre solid mounted but that transfers all that force into the axles and springs - just the same as solid transfer mounts transmit more force into the transfer gears. Many years ago Petersens built a Chevy avalanche for ultimate adventure. They had issues with axlewrap and after UA they put a traction bar in it... and it destroyed the ring and pinion. Some give is helpful to soften the hits the driveline sees.

No we never built a bar because it was clear it was going to bind up. It ran with nothing until Greg installed the strap. It's not the same thing as having a bar because you can decide how far the axle wraps before you put any influence into the springs. through the normal range of motion it doesn't influence the springs at all and sits slack. As the pinion starts to rise it tightens up. I'd try one in your application before I built a heavier/more complex bar that absolutely will influence the springs at some point.

Something to consider - (about the force these bars are dealing with) - everyone I know of who was mounted a bar to the stock chassis crossmember has had it tear out and/or bend the crossmember. There's a heap of force being dealt with by a traction bar.

[Beery]

cool, that all makes sense.

Gwagensteve wrote:

I'd try one in your application before I built a heavier/more complex bar that absolutely will influence the springs at some point. .

I think i might. Axle wrap isn't a huge deal on my car, but it's enough i want to do something about it. Less work and weight is also very appealing.

How have you guys best found to set the strap up? my car has roughly 50mm of compression travel at ride height, so I imagine the strap shouldn't have much slack. Maybe even a tiny bit of tension to preload it a bit?

Is the strap in gregs car mounted to the carrier? any reason for that over the housing. Also, if I was to do this, would I be better off getting the mount at the diff end up as high as practical so it has more leverage/control over the pinion?

[Gwagensteve]

It"s mounted to the A Arm mount (Greg runs a Vitara rear diff). It works well. Definitely take into account that the straps stretch once used so give yourself plenty of scope for adjustment (hence the clevis on the axle end)

Definitely getting the axle end up as high as practical will reduce the load on it.

[Beery]

Ahhh, of course.

Alrighty, thanks for the info. I'll update with whatever I go ahead with.

[greenzook89]

Wilso ran a track bar on on Edna back in the day. I've seen it in action a few times and it did what it was supposed to do but the back end was stiffer with it vs without, scroll halfway down for pics/info.

viewtopic.php?f=4&t=50144&hilit=edna

I had all the bits like boggas to fit into Redna but never went ahead with it before wrecking the car.