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LOUD Rear Vibration or Hum disappears with rear Drive shaft removed

can you snap a picture of your driveshaft and pinion straight from the side so we can see that angle where they meet?
 
Sure I can do that for the post sake and for others. The rear shaft isn't currently in there so it won't be today. But there is absolutely no way you can tell if my pinion angle is correct through a picture. You may see if it is way off, of which I can assure you its not.
Pinion angle is not rocket science (although I believe many get it wrong including myself on a previous jeep) and I've adjusted and readjusted it just to make sure. Measured with analog and digital angle finders even a tape measure and some math. I've even mal-adjusted it several degrees on purpose without any change in vibration.

There are about 5 of us friends who wheel together and my buddies are engineers and far more skilled mechanics than I, they have all looked at it as well, problem is they live about 4 hours away so don't have time to troubleshoot this whole issue with me.

But I'll shove a photo in when I get a chance, maybe something else will catch your eyes and lead to a new idea.
 
no worries, just wanted to make sure you're setting it for a double cardain shaft instead of the stocker. it's completely different.
 
Yep, pointed nearly straight at the t-case with a degree or two down for torque of the axle, instead of parallel to the t-case output as would be done for stock DS.
 
ok cool no need for pics then. sucks you cant solve it, i'd be going crazy.

when you rebuilt the driveshaft, did you make sure you put the spring back in the centering ball?
stupid questions, but shit, it seems like you got everything else checked out.
 
I know right! I have been going crazy a bit, its really killed my joy for this machine. I have a hundred other "fun" projects for it I've put on hold to fix this dumbass problem. Got parts laying all over the garage to be installed. Like everything for a WJ knuckle swap, and winch, exo cage.

Your the first that knows about the double cardan. Yea, it the new piece came with a new spring and I made sure all the needles were in place.
 
Dustys said:
And for those who have never taking a double cardan apart, mine has a sealed ball side (that was replaced) that slips over a stud in a socket on the other side of the double cardan.
Click to expand...

i believe you are talking about the centering ball.

i was unaware of this the first time i did a shaft. i lost the needles out of the ball. $50 for a replacement that i had to press in to replace the old one. while the whole assembly was like... $45 from spicer. alas... i did not have the time to wait on an order. moral of the story... dont lose the needles out of your centering ball!
 
I think it has to be your driveline angle. That said, couple things that come to mind...

Check your transfer case mount to be sure it is the correct one. If you have the wrong one, it will shift your tcase over an inch or so, which will put your driveline angle off side to side.

Second, if your motor mounts and transfer case mount are shot, the tcase could be moving so much while under load that it fouls up your driveline angle.

Good luck, don't give up, and keep us updated.
 
Sounds stupid, but rotate your tires and see if the issue changes.

I installed a Tom Woods SD SYE and XB shaft and still had vibes after installing a lift that netted over 4.5". Shimmed the rear axle 4°, still had vibes (just about as bad too).

Rotated my tires on a tip from someone here and the issue went away. I guess driving a few thousand miles with the stock shaft after lifting caused some weird tread wear.

No clue, but try it. Takes 10 minutes.
 
Going to get a new driveshaft from Tom woods this week, even tho mine has been rebuilt and balanced. Ive heard they only balance to 1500 rpm and if mine is spinning closer to 4500 the. That may be the problem. In addition I'm going to raise the jeep up and running up to speed without the tires on. See what turns up.
 
Check The Mounts

Hi there,

I'm at work so I could not scan all 4 pages yet but...

Did someone mention to check Motor and Trans Mounts?! A little vibe can get a whole lot bigger with rotted/wasted mounts. I had a little that got nuts at 55-60 and even after I balanced and swapped out U joint parts it was present at 60 or so.

I swapped out all the rotted mounts and it was not only smooth, it drives so well without the powertrain flying all over the place (imagine that right?).

Anyhoo, as countless others always say, just replace those three mounts now so they don't haunt you at a bad time later. :thumbup:
 
That's a good point. Thats on my list next. Harmonic vibrations are the sum of all vibrations. Pistons, crank, transmission all have slight imbalances and when all those sync up they can really shake. So yes I will do the mounts.
 
Not to highjack the thread topic.......but on a related note:

You can pump the voids of the new motor and tranny mounts full of Loctite PL S30 Polyurethane Roof and Flashing Sealant ($5 a tube at HD) before you install them to make them less prone to stretching over time.
This product has a hardness rating of Shore 27.5, whereas most aftermarket poly mount stiffness ranges between 60 and 90.

Let the poly cure for 3-4 days for best results. Stock motor mounts stretch a lot under load, filling the void reduces their ability to stretch and lenghtens the lifespan of the mount.

You can even give your old mounts a "po boy tuneup" if they aren't torn.
 
I am waiting to hear what you did to rectify your problem because you are describing my situation that has the EXACT same symptoms....hurry up would you :)

Hans
 
Drives me nuts. These threads are better than mystery novels to me. I *need* to know whodunnit.
 
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