Eyeball my pinion angle please!

Chances are that the harmonic has always been there, but was dampened by the rubber mounts. The failing u-joint may also have created new damage that now is rearing its head, with the poly mounts amplifying the vibe. Pull the rear drive shaft and check the torque of both the TC output yoke and the rear diff yoke. Also check for up/down, in/out play in the yokes. Maybe the bad u-joint smoked the pinion bearings.
I feel your pain brah. Been chasing a harmonic of my own since re-gearing.
 
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bobthetj03 said:
Chances are that the harmonic has always been there, but was dampened by the rubber mounts. The failing u-joint may also have created new damage that now is rearing its head, with the poly mounts amplifying the vibe. Pull the rear drive shaft and check the torque of both the TC output yoke and the rear diff yoke. Also check for up/down, in/out play in the yokes. Maybe the bad u-joint smoked the pinion bearings.
I feel your pain brah. Been chasing a harmonic of my own since re-gearing.
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Yeah it sucks! No play in the yokes, I will check the torque in a bit though. I had some vibes with the old rubber mounts, but the driveline was completely smooth prior to that u-joint failing. There are some other issues that I'm having, I created a new post earlier today about a strange noise that I'm hearing from the trans or t-case, but I don't think that it's related.

I'll probably wind up selling my Jeep if shit like this keeps dominating my free time and budget. I can't spend more tim fixing and diagnosing problems than driving.
 
One other thing that may or may not play into this - could greasing the slip joint have caused an imbalance? That was another variable I did not mention. Also, can't find anything definitive - how much grease should I be pumping into that guy?
 
I don't think greasing the slip joint would cause anything like this. I'm almost thinking that this vibration was here all along, you're just only now noticing it because of the poly mounts.

As far as how much grease goes, pump it with grease until it just barely starts to come out, that's what I always do. Then I just wipe away the excess and I'm good to go.
 
Noticed the drivers side UCA bolt was very loose. Before I go to town to un-seize these cursed jam nuts, has there ever been a case where a loose retaining bolt has been the source of vibrations?

Also, my UCAs have always felt pretty loose on the mounts and rotate freely at all times by hand (no up / down / lateral play, just super loose rolling action).
 
jeep_boss said:
Noticed the drivers side UCA bolt was very loose. Before I go to town to un-seize these cursed jam nuts, has there ever been a case where a loose retaining bolt has been the source of vibrations?

Also, my UCAs have always felt pretty loose on the mounts and rotate freely at all times by hand (no up / down / lateral play, just super loose rolling action).
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Jerry Bransford said:
Sine wave? That's a pretty pure smooth signal. ;)
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Since wave with an LFO creating peak every 3 seconds
 
Got one of the bastards loose. Had to buy an 18" Crescent with a 2 3/4" jaw. What's the rule on anti-seize with these?

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It's better now. I rotated my rear axle down a little - the harmonic vibration starts around 68mph, but it not intense. On a scale of 1-10 (10hi), before it was about a 4.5 in intensity. Now it's more like a 2.5.

I'm left with a couple of questions:

  1. Will there always be some kind of harmonic vibration with poly mounts? If so, what isn't "acceptable" and should be fixed?
  2. Are the poly mounts going to rattle my Jeep apart over time? They can get pretty intense, I don't mind them that much but I feel like I'm going to need to do routine re-torquing of components, especially in the cabin!
Trying to find the source of vibrating cabin parts is a nightmare.
 
NSG370 perhaps? There's a good chance the harmonic vibrations could be from trying to turn those 35" tires with 4.11 axle gears. It's usually an an 03-06 auto tranny issue once you get to 33"+ tires on the stock axle gearing due to the engine lugging with the .69 overdrive, but I'm just throwing that out as a possibility, since you said it's when using 6th gear. Big tires for 4.11 gearing...
 
glwood said:
NSG370 perhaps? There's a good chance the harmonic vibrations could be from trying to turn those 35" tires with 4.11 axle gears. It's usually an an 03-06 auto tranny issue once you get to 33"+ tires on the stock axle gearing due to the engine lugging with the .69 overdrive, but I'm just throwing that out as a possibility, since you said it's when using 6th gear. Big tires for 4.11 gearing...
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Derp, yes NSG370. Sorry, I've had my NV241 staring in my face all day!

I think I have the harmonic vibration issue fixed. I may consider going back to torsion rubber mounts though - the rattling in the cabin may start getting to me. Poly mounts might also depreciate the Jeep, so I don't know if I should keep them on.
 
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jeep_boss said:
Derp, yes NSG370. Sorry, I've had my NV241 staring in my face all day!

I think I have the harmonic vibration issue fixed. I may consider going back to torsion rubber mounts though - the rattling in the cabin may start getting to me. Poly mounts might also depreciate the Jeep, so I don't know if I should keep them on.
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That would be my next step, personally. Poly mounts are evil.
 
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Jerry Bransford said:
Are the u-joint bearing caps centered in and properly seated down into the yokes? Not being seated down inside the nubs pointed to by the arrow will cause a hard to isolate vibration.

And there's no chance the pinion angle could be a tad above the driveshaft is there? Better the pinion angle be pointing a tad under that of the driveshaft angle than a tad above the driveshaft angle.
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I decided this afternoon to rebuild my rear DS and make another adjustment to my UCAs (I went two full revolutions smaller yesterday, which had put me -3'ish below my DS). You kinda motivated me to just rebuild the CV - and having a stack of new 1310x's, I did just that.

I put my driveshaft back on and turned back my UCAs a full revolution - putting it a single rev tighter than it originally was. This put my rear axle pinion exactly -1 degree... this is where it had sat prior to the poly mounts.

Bolted everything up and took it out on the freeway. It now runs PURRRRRRFECTO!!!!!!

Can't thank you all enough, especially Mr. @Jerry Bransford - muchos tacos amigo!!!!
 
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