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Discussion Starter #1 (Edited)
I recently swapped in a rear diamond axle on my runner with all custom adjustable links. The links are all factory lengths to match the angle of the factory axle.

The issue I'm having is at I'd say 40+ mph, If I let off the throttle and begin to coast I get a subtle vibration/rattle. It makes the noise instantly and more aggressively when I get back on the throttle but not when driving normally. There's also some sort of sweet spot in the throttle to create the noise constantly.

I jacked the rear end up to replicate the noise so a friend and I can investigate where it's coming from and it appears it's within the driveshaft. I checked the ujoint and it has zero play. However, I noticed the slip yoke has noticeable wear around the shaft where it use to sit inside the driveshaft. Telling me that it's extended the slip yoke out after I put the new axle in. Keep in mind, I did not remove the slip yoke from the ds so it's alignment has not changed. I also checked the gears and there's no obvious wear or chipped teeth.

If you grab the ds near where the slip yoke goes in you can feel some slight movement, like there's a small gap.

My main thoughts are:

1- The slip yoke threads are not engaging enough
2- The slip yoke male splines are worn along with the above
3- The phasing is off due to the axle housing being slightly rotated

Any other ideas on what could be causing it the noise? Here's some pics of my ds angle.





Here's the setup

 

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CV at the Tcase side? Or no CV? X2 on pinion angle if it's a CV shaft or phasing. Driveshaft balanced and not bent? Looks like some good scrapes on it.

Also are you running stock bushings for your link mounts or harder poly bushings? If so it could be transferring noise easier with harder bushings.
 

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Since you feel play in the slip, I would grease that up first. I would also adjust the upper links, possibly lowers and get the pinion up a touch. I know our fixture for link locations is referencing pinion angle, so that should be right on where it was.
 

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Discussion Starter #7 (Edited)
CV at the Tcase side? Or no CV? X2 on pinion angle if it's a CV shaft or phasing. Driveshaft balanced and not bent? Looks like some good scrapes on it.

Also are you running stock bushings for your link mounts or harder poly bushings? If so it could be transferring noise easier with harder bushings.
No cv.. Sorry, I worded my last post weird. Single cardan at the diff, and double cardan at the case. Haven't had the driveshaft balanced. Probably wouldn't hurt, to smooth up the ride, but I don't think that's what's causing this.

The links are chromo heims with misalignment spacers. So yes, maybe any previous driveline vibs were softened by my factory rubber bushing links. I feel like this is new though, as it's not something that I feel could have been softened or quieted by that.
 

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Discussion Starter #8 (Edited)
Since you feel play in the slip, I would grease that up first. I would also adjust the upper links, possibly lowers and get the pinion up a touch. I know our fixture for link locations is referencing pinion angle, so that should be right on where it was.
Thanks.. Is this pinion angle an absurd amount? It's clearly not necessarily aligned looking straight at the case but I figured that's what the u-joint is suppose to do to, to provide "wiggle room" for it.

Sounds like worst case scenario, I lengthen the upper links and shorten the lower links by a few turns and get the pinion angle up. I'll grease the SY up first and try that.
 

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I see what you're saying.. It's single at the front and dc at the case.
CV at the Tcase side? Or no CV? X2 on pinion angle if it's a CV shaft or phasing. Driveshaft balanced and not bent? Looks like some good scrapes on it.

Also are you running stock bushings for your link mounts or harder poly bushings? If so it could be transferring noise easier with harder bushings.

Looks like he means DC at the T-case. In that case, the axle pinion flange should be pointing up towards the t-case.

You look to be set up for a single at both ends. Check your degrees, Depending on your caster, it may be easier to change front drive shaft.
 

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It isn't the tcase output bearing. Its not the joints. Is it the diff input? No? I do know that if you can feel it in the butt, it will kill all of the above in time.

Well... If you figure it out pm me. I'd really like to know. In a fit of "fucking piece of junk" I just added a LOT mor preload to the diff and it was 90% reduced.

Diff makes a weird rururur noise now while coasting. Exactly as fast as the tires.


Sigh.
 

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Discussion Starter #11 (Edited)
It isn't the tcase output bearing. Its not the joints. Is it the diff input? No? I do know that if you can feel it in the butt, it will kill all of the above in time.

Well... If you figure it out pm me. I'd really like to know. In a fit of "fucking piece of junk" I just added a LOT mor preload to the diff and it was 90% reduced.

Diff makes a weird rururur noise now while coasting. Exactly as fast as the tires.


Sigh.
I do believe you're 100% correct. Ignoring it will likely cause more issues down the road.

I'm pretty certain it's the pinion angle and the phasing being off. There's just enough stress on the slip yoke where it goes into the DS it's causing some vibrations. It's also likely that's it's transferring those vibrations elsewhere as well. Plan to adjust the pinion angle this weekend. Will report back.
 

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If you have a double carden at the t case, your pinion angle is wrong. Double carden is also referred to as a cv. While it is not technically correct, it is a common term we use. U joint phase could be an issue. But i just looked at the first few posts and left this post.
 

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DC at Xfercase needs 0 deg pinion angle. Also, phasing is not as much of an issue with double cardan driveshaft. Would be nice to have a trac Bar, to protect that expensive driveline! (Just my humble opinion)
 

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Discussion Starter #17
This is a real good write-up on driveline basics!!

Driveline 101

How do you know your u-joints are good, feeling them tells you nothing, you have to take them apart to be sure!!
Thanks.. The u-joint aren't that old and if there's any amount of play you can usually tell. Their tighter than a bull's asshole in fly season :D

DC at Xfercase needs 0 deg pinion angle. Also, phasing is not as much of an issue with double cardan driveshaft. Would be nice to have a trac Bar, to protect that expensive driveline! (Just my humble opinion)
I've come to realize that haha. No reason for a trac bar with the panhard. Keeps the axle from shifting side to side under normal driving conditions.
 

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Discussion Starter #18 (Edited)
Thanks everyone for the help. After tinkering I was able to get the pinion angle up and adjusted my upper links accordingly. All the drive-line vibrations and noises are gone!
 
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