Axle Wrap

Trying to get my head around it. I’m having issues with it, in that when I accelerate hard, I get a lot of vibration. I’m looking into traction bars, but not easy to find for a ‘75. Am I trying to control the springs or the diff angle? I have an idea on how to control the diff, but wonder if it would put strain on the axle tube at the diff as the springs would be free to do whatever they want… hope I’ve been clear

 

What is your suspension set-up? Axle wrap (axle rotation up/down…rear pinion movement up/down under acceleration) is most common on a lifted rig with soft springs and extra hp…and on SPOA suspensions. I would think you need to keep the spring from flexing in the center.

WFO sells a torque arm kit that you’d have to do fab work to install.

There are also special, longer spring perches out there to add rigidity to the spring and prevent a leaf spring from flexing in the center.

Of course there could be other causes of vibrations in the drive train as well.

 

Rough country 2 1/2 lift. DC driveshaft. Cruising down the street is fine, minimal vibration. The springs seem pretty stiff. I have an idea for something I can just bolt on but it would control the pitch of the diff and do nothing for the springs. That’s where my concern is… would that stress the axle tubes at the diff ?

 

I would not think so. A torque arm is pretty common way to stabilize a rear axle experiencing axle wrap. These Dana 44’s are pretty strong. How big are your tires?

 

Certainly it also depends on how you use the thing and how much abuse you’re putting it through.

 

I’m running 30x9 and it’s just my grocery getter

 

Stock tires, pretty small really. Sounds like you have a solution.

Just to cover the bases....What is the pinon angle? I believe it should be pointed towards the TC case output with a DC driveshaft.

Not saying axle wrap is not your problem, just that it might be other things. Axle wrap usually feels like a clunk, or grabby tires or lurching.

 

A picture of your rear shaft from the side would answer a lot of questions.

It sounds to me like your pinion is pointed up a few degrees too far. Ideally you want it about a degree below level with the driveshaft. As you apply torque to the rear, the torsion will level the shaft. If you start with a shaft that is perfectly in line with the pinion, it will go past its comfort zone under power and vibrate.

 

I’ll check. I do have 8 degree shims in. Maybe it’s too much. I get what you’re saying about the angle… thanks

 

Just a thought here........... How's your clutch ?

 

It seems to work fine. Why do you ask

 

Not perhaps in this case, but I also found with the asymmetrical Holbrook springs that the angle of the spring perches also changes with travel. That made an interesting install with a really short rear driveshaft with the normal "aiming" ending up several degrees above the tcase at full compression. A life of compromises in that one.

 

I've isolated axle wrap from pinion angle by clamping the springs with C clamps. If the pinion is rotating past 0 degrees it will cause a vibration under acceleration. Ron

 

Noticeable vibration on acceleration is almost always associated with the driveshaft. Are the U-joints stiff or too loose? Are the joints “in phase” with each other?. Are the slip-joint splines stuck or too loose?, Then pinion angle needs to be correct.
I have serious doubts that traction bars would be of any help. You have issues with the the driveshaft, or its angle to the pinion.
-Donny

 

It’s a new DC driveshaft. I have yet to check the angle, but it looks close, and the shop which installed it is reputable. The only thing I can think of is the pinion angle changing on acceleration

 

Reputable shops can make mistakes too. Tom Wood's Drive Shaft has some really useful tech articles. It's worth reading though them.

Tech Pages

Diagnosing Driveline Vibrations

Single and Double Cardan Geometry

Here is a VIDEO of Axle Wrap. Note the soft springs on that YJ. And a video of a SPOA JEEP (from Tom Woods Website). Rough Country ECJ5 springs are pretty stiff, they are military wrapped and you have relatively small tires. It might be worth trying to video tape your drive like they did here if you still think this is your issue.

 

Agree on the shop possibly making a mistake. Videoing the springs is an excellent idea… thanks

 

the difference in angle between the DS and pinion is around 1.4 degrees

 

It’s possible but with your suspension setup axle wrap should not be an issue. I’d take a look at your transfer case and cross member mounts as well as making sure the new driveshaft is in phase. (I had one arrive that was not)

 

Typically when using a double Cardan Cross joint at the transfer case I set the pinion 1/2 to 1 degree down so when the pinion climbs under load it will point close to the transfer case. Depends on other factors of course but in 35 years of setting these up it has worked well for me.