Driveline noise

Hello all,

For the past few years my bronco has been an off and on project.  I broke a rear axle and ended up on the roof at the last mud race I went to several years ago.  I slowly got the truck back together and had another accident at the local drag strip.  I broke another rear axle, went into a spin, and hit the guard rail.  Once again I've gotten the truck back together.  The theme of this story is much more work than play for the past few years along with some bad or good luck depending on the way you look at it.

Anyways, I have had a vibration in the t-case/ rear driveshaft area for the past few years.  The noise is only present while in 2wd and coasting at speeds above about 35mph.  When you get on the gas it goes away and when you let completely off the gas it goes away.

I put a twin stick kit on the transfer case to rule out a worn shifter linkage and the noise is still there.  I have put a new gear set in and the noise is still there.  I cut my spring perches off and have the pinion angle matching the transfercase output to within 1.5 degrees.  The transmission has been rebuilt.  I have new joints in the driveshaft.  I even swapped transfercase a few years ago and the noise was still there.

Previously the truck had a 1310 I( believe) cv joint at the tcase.  I had a 1350 traditional non cv style driveshaft built when my old cv took a dump.  This was for strength purposes.  If I'm not mistaken, this is about when my noise started.  But at the time I had a failing rear gear set, trans etc, so the driveshaft wasn't on my radar.

The angle between the driveshaft and tcasetcase output is 20 degrees.  This is due to my short wheel base.  The truck only has an add-a-leaf for lift in the rear.

Do you guys have any idea where this noise is coming from?  Can 1.5-2 degrees of mismatch in universal joint angles cause this type of vibration?  Does the steep 20 degree working angle magnify this phase angle discrepancy?

The only thing that has made the noise go away is to take the rear shaft completely out and drive down the road in 4wd. It's quiet as a mouse then! It is also quiet going through the gears in 2wd with the shaft out.(just sitting in the driveway). This thing is about to drive me crazy.

My next thought is to have the balance checked on the driveshaft as well as straightness.

Any help is greatly appreciated!  Thanks!

Jon

Check for joint bind. We found with the short drive lines in a bronco the bigger joints bind when driving. It'll make a very small shiny spot where the ring around the cup touches the yoke of the rear diff and or the trans.

Mine does the same thing, also after going to a non cv 1350 driveshaft. I even ran it on jack stands in gear and could hear it plainly when coasting, could just touch the brakes to load it and the noise would go away.

I haven't seen any damage from it so i just ignore it. Rather have it then puke the H yoke out periodically like it used to.

That makes me feel so much better norm! I've got a few more ideas I'm going to try. I turned the shaft several different orientations and also built some shims to perfectly match the pinion and t-case output angles. The noise is better, but still present. Thanks again for the input guys!!

Jon