Axle Wrap or ???

[CBNFPRT]

Went for a quick stint up to Rowher Saturday and took a newbie up in his stock Taco so didn’t really do anything worth mentioning except I did one obstacle I’ve done many times with no issues. I did get into some loose stuff half way and had to renegotiate the line, but didnt do anything aggressive like mash the go pedal and sit there spinning. I now have a pretty wicked vibration at 50mph and up so immediately went to rear u joint thinking it might need to be reseated and came across these fresh wear marks. Is this a byproduct of axle wrap or would it be more likely the rear flexed low enough to cause a bind? It’s a well worn 302 and have Duffs rear shock mount that mounts to front of axle that’s suppose to help with axle wrap so I didn’t think I’d worry much about that. Being that I didn’t do anything nearly as gnarly as Calico or BBBB and first time ever seeing this on the u bolts and yoke and the u joint is probably toast, I wanted a second or third opinion before I start throwing dunkets at an anti-wrap setup...

Also the rear axle is shimmed 6 degrees to accommodate the 2.5” lift.

 

[ntsqd]

Are your u-bolts tight?
Are both of the pinion angle shims still there?
How is the rest of the drive-shaft? Slip still tight?

I can't think of anything other than wrap that would cause contact like that if everything else is good.

 

[CBNFPRT]

Yeah everything is still there and tight. Just seems odd for this to occur on a trail I’ve done many a times with this setup. Specially since I usually hit all the “hard” spots and this time I took it easy.

Now the great CB.com debate... Duff’s torque tamer, WH wrap trap, or ???

 

[ntsqd]

If you actually plot the pinion angle vs. suspension travel you'll find that the ladder bar, even the ladder bar with a shackle at the frame end doesn't follow it correctly. Which is to say that the ladder bar is forcing the springs to 'wrap' up in extension and 'down' in compression. Without a ladder bar the pinion angle does change, but nowhere nearly as much as it does with a ladder bar - shackled or not. Those with a ladder bar can do a simple experiment to see this. Pull the front bolt and run the truck up a ramp. Then compare where the end of the ladder bar is vs. where the hole(s) in the mount or shackle are. Turn the truck around and back it up the ramp. The more the bar is off to one side the more of a difference there will be where the end of the bar will be from ramping in the two directions. Some of the K5 crowd were shearing 3/4" G8 bolts at the front end of their ladder bars when on it hard. That's pretty impressive.

The only way to get away from this is to make housing rotators for the leaf spring mounts. Then the ladder bar isn't fighting the springs for pinion angle control.
Better off to make it more or less a parallelogram. Which is what the Wrap-Trap does. The trap's bar is in tension and it puts the main leafs in compression, which will bow them a little since they're already curved.
I made the argument a number of years ago that if you need more than what a Wrap-Trap can do (i.e. you're flexing the main leafs to the point that you're breaking them) then it's time to figure out linkage. Guys like 'nvrstk' have been down this path and verified my statement, but we still debate this. I think it's mostly because of ego and a sense of investment.

 

[CBNFPRT]

Yeah so I don’t get it... Just went through the rear end triple checking/tightening everything and swapped out u joint and the vibration actually seems worse! Starts now at 35 mph rather than 50... quite aggravating.

 

[ntsqd]

Put it up on jack stands under the rear axle housing (pointed OUT of the garage!) and run it up to those speeds? OR put a Go-Pro under there (maybe with more than one location option) and take it for a drive?

 

[CBNFPRT]

Turns out I managed to bend the shaft.. put back to shape and rebalanced via Driveshafts A-Z in Valencia. Highly recommend them.