I hate to be the bearer of bad news, but over the axle traction devices do NOT stop axle wrap and will not help with the driveshaft issues. We tested that same design over two years ago. I made a very detailed post not long ago explaining the pros and cons to all the different traction designs, but since the search is down, I can't find it. Let me try to quickly refresh what I had posted in referance to the over axle design...

When the axle rotates or "wraps" on acceleration, what you have is an arc movement. The pivot of the arc, is where the axle housing attaches to the spring, and the actual arc is at the bottom most part of the axle. So if you are looking at the truck from the side with the wheel off, imagine the spring as a horizontal line, and the axle as a verticle line going straight down. Since the axle is held in place by the spring, the bottom of the axle is what moves. As you get farther from the spring, more leverage is exerted on the "pivot" point, making it easier to move the axle.

Most traction devices connect under the axle. By connecting UNDER the axle, you are holding the part of the arc with the most leverage from moving. Therefore you stop ALL movement and stress on the pivot point.

When you use an OVER the axle traction device, you are holding the axle AT it's pivot point. Nothing is stoping the axle from arcing, and you still have the same leverage as if you had no device.

Here's a quick test you can try right now, to show what I mean-- take a pen or pencil and hold it in front of you, straight up and down. The part pointing up, is going to simulate where the axle attaches to the spring. The part pointing down, is going to simulate the bottom of the axle. Now hold the pen/pencil at the BOTTOM with one hand, and with the other hand, grab it right above where your other hand is holding it. No matter how hard you try, you can't move it, because you are holding it at the same point that's trying to rotate. Now take one hand and hold the pen/pencil at the very TOP as hard as you can. With your other hand, grab the bottom and try to arc the pen/pencil. No matter how hard you hold the top, you can still move the pen/pencil. This simulates an over axle traction device.

Keep in mind that I'm just trying to show people why that design doesn't work, because we've tested it in the past. I also know several people using over the axle traction devices and they are still breaking driveshafts. Just a little FYI.

 

Sal I'm a little confused here Doesn't any device that stops axle rotation prevent axle wrap? Either on top or on the bottom of the spring. Both setups allow vertical movement while stopping rotational movement. They are both ridged to a twisting force. If an over the axle setup is mounted correctly I don't see how the rearend will twist unless the axle tubes are flexing. With that in mind how can you break a DS by having the rearend pinion go up too high on acceleration? Jeff

 

That is correct. What I was trying to show is that over axle traction devices don't stop axle rotation. Re-read my post and try the pencil demonstration and you'll see why.

As for the driveshaft issue, when the axle wraps up, it points the pinoin upwards towards the bed. What that does is two things. One, is transfers a ton of torque to the u-joint which can cause joint failure, and two, it puts stress on the shaft, which can cause failure. The reason for this, is because with the rear end twisted up, you no longer have a straight path of torque from the driveshaft to the rear end. Power basically now has to exit the driveshaft, then make an angled turn to the rear end through the u-joint. And since the rear end is pushing up on the shaft, it puts additional stress on it, to where it will usually fail at it's weakest spot, the center.

 

Mine failed at the holes on the shaft. I guess the U-joint was stronger than the shaft!!

 

That's a good point. On the aluminum shafts, the "ears" that the u-joint fits into are also aluminum. When you twist the rear up, you are not only stressing the joint, but the ears of the yoke on the shaft as well. We've also seen where the ears on the rear end yoke contact the bottom of the shaft yoke, from being twisted so far to the side.

 

For starters, the spring should not be considered an "anchor". An "anchor" would suggest an immoveable point. The spring, during lauch, actually distorts in FRONT of the axle thereby allowing movement. That movement allows the BOTTOM of the axle to move forward (wrap or windup) even with a traction or control bar mounted at the TOP of the axle. With a BOTTOM mounted bar (which would be considered an "anchor" if installed properly) the TOP of the axle is forced to travel BACKWARD, which it cannot because the spring will not stretch. Hope this helps.

 

EXACTLY!!!

I fixed this 3 ways..

One having the smaller Steel shaft will allow more room for travel.
Two Installing the PSP Jay Lincoln Truck Tracs to prevent Axle Wrap
Three Changing the pinion angle so that its is alittle negative and under load it will be right on the money when limited by the truck tracs!!!

 

Also the front of the spring has a solid mounting point, where the rear of the spring is mounted on a pivot(shackle)

Maybee this is why a lower mounted traction bar stops axle twisting better.

 

How can the bottom of the axle move forward if the top of the axle is stationary? Do the springs stretch? Just curious....

 

Because the top of the axle is NOT stationary. The springs distort and reshape themselves based on the load that's being applied. As Don pointed out, the rear of the spring is mounted to a pivoting shackle. The spring is not held in one position. Having an over axle traction device will not stop that distortion.

 

The springs Do Not stretch, but under severe load they will distort or compess. This only happens to the portion of the spring that is in front of the axle. Sooooo.... If your bars are mounted at the top of the axle........ and the spring compresses forward(thru distortion)........ you have axle wrap!

 

Ok, I think this would be better explained visually, so I drew up a quick sketch to help explain better...

Picture 1 shows a normal rear in it's normal position.

Picture 2 shows typical axle wrap. The part where the axle attaches to the spring acts as the pivot point of the arc, and the bottom of the axle arcs forward.

Picture 3 shows an under the axle traction device. The axle housing is now held at both the top and bottom and cannot twist.

Picture 4 shows an over the axle traction device. All this does it give the arc a higher pivot point, which now makes the spring absorb part of the arc, and distorts the spring both in front and in back of the axle. Nothing holds the bottom of the axle, and you still have axle wrap.

Hopefully this helps explain the difference between the two. I just hate to see people spend money on something that won't solve thier problems.

 

I guess a picture is worth a thousand words....

Nice Job.....

 

Thanks for the visual Sal....I understand the theory now...