anti wrap bar questions

[Marduk49]

so i just bought my first FJ40 (from Gillti) awesome love it, runs great, its a 1972 FJ40, 1978 Engine Swap, SOA, 35's, 8274 a few weeks ago anyway took it out and snapped the rear pinion... people have been telling me i need to install a anti wrap bar. seen a few different designs, one in particular that looks like the winner
http://www.jeepaholics.com/tech/bambar/, anyway this is for a jeep with the diff right in the middle but was wondering if anyone has seen something like this on an cruiser with the offset diff, or any other ideas that aren't going to limit my articulation

 

[burl40]

In my opinion I would run a ladder bar type like the website describes.A upper and lower mount to the axle and a single pivot attatched to a shakle.It is possible to use your crossmember for the front shakle hanger position.

 

[ntsqd]

The rear axle housing travels in an arc of a non-constant radius due to the main leaf's arc flattening out and curling up through the travel range. With a little effort a constant radius length and center point approximation can be found.

The ladder bar designs all force the pinion to point to pretty much the same place (+/- what the minimal travel arc of the shackle allows). This means that the springs must take on an 'S' shape to accommodate the ladder bar or the housing must twist between the ladder bar mount and the spring pads. This is true even if the ladder bar length is that of the approximation's radial length and it's shackle end is in the approximation's center point location. Eventually that bending will kill the main leaf/leaves. In some cases the forces involved were grossly under-estimated and many sheared bolts of seemingly reasonable size was the result.

The "Bambar" design could have less of the spring bending problem, but the horizontal shackle's length and it's pivot points need to reference the approximation's length & center point as well as parallel a straight line from the center of the front spring mount to the center of the axle housing.

By the time you've done all of that with a Bambar design you may as well just build it as a single link with a pivot attached to the frame at the approximation's center point, at the approximation's radial length, and with the housing pivot position set such that the bar is parallel to the straight line mentioned above.
The Wild Horses "Wrap Trap" is exactly this design, but unfortunately for 40 owners it's lengths etc are optimized for Early Broncos and is not likely to be a short-cut.

 

[playhard]

Have you looked at something like the traction bars at Sam's off-road?

http://www.sams4x4store.com/tractionbars.htm

The installation does require you to weld 2 plates to your axle. You could weld them anywhere along the length of your axle. I know of many Jeeps running his traction bars, including mine. I have never heard of a problem with them. The only fj40 I personally know running his traction bar is also running Dana 60 axles.

 

[cumminscruiser]

anti wrap

Here is a picture of one I saw a the LC sawp meet last year. I'm building a simular one with 3 points instead of two. I dont know which is better I just have the parts for the 3 point. I was able to buy flame cut cool looking brackets just for that application at a near by 4wd shop.

 

[RHINO]

arguements rage back and forth about the 2 vs. 3 point bar, i think 2 point for SUA 3 point for SOA. thats my pennies worth.

 

[cpg]

Marduk49;310990]so i just bought my first FJ40 (from Gillti) awesome love it, runs great, its a 1972 FJ40, 1978 Engine Swap, SOA, 35's, 8274 a few weeks ago anyway took it out and snapped the rear pinion... people have been telling me i need to install a anti wrap bar.

It would also be a good idea to upgrade to a fine spline pinion at least for the rear diff.

 

[rusty_tlc]

Have you looked at something like the traction bars at Sam's off-road?

http://www.sams4x4store.com/tractionbars.htm

The installation does require you to weld 2 plates to your axle. You could weld them anywhere along the length of your axle. I know of many Jeeps running his traction bars, including mine. I have never heard of a problem with them. The only fj40 I personally know running his traction bar is also running Dana 60 axles.

For maximum articulation and minimum stress on the components the axle end should be as near as possible to the center of the axle.

 

[Max]

Here' some pics of my home built lader bar, base on the same model you link:

my Fj-40 is a 1980, SOA and 36" swamper

 

[Marduk49]

thanks all for the info its been very helpful. i think im going to go with something similar to the sam bar thing. My roommate is a mechanical engineer so were going to try and do some measurements and calculations to determine the optimal length for the bars, so that the pivot happens at the right spot. but im guessing its not going to make that much of a difference than if i just welded on a bracket like max's home built ladder.