Front driveline vibration

[Rickstar321]

I've heard this is common... but not convinced. I have an Adams, I'm only on 2-1/2 inch OME coils, 1" motor and body lift, flat belly tummy tuck.

I have a very slight 3 second low to high to low drive line vibration... 3 seconds on... 3 seconds off... but just around 64 to 70 mph.

I drive my TJ across country to wheeling events and I'll even disconnect the front driveline due to the pulsing vibration.

Note: I'm in the beginning stage of a JL axle swap and have decided to keep the FAD due to the already less than desirable caster angles for the M210.

My point to this post is just wondering how common the front driveline vibration is for TJ's?

 

[Unique Username]

If you’re in the beginning stages of an axle swap, I would wrap that up 1st as it seems redundant to diagnose the issue only to start over with new front pinion adjustments.

 

[GoldenGorilla]

I have a similar thrumming vibration pattern with my Rubicon starting a 72mph and increasing upwards from there running 285/75R16s on 4.56 gears. It used to start at 80mph when I ran 4.10s and was a thing I rarely encountered, but knew was there. To be clear, this is not a massive teeth rattling vibration, but it's not "a jeep thing" I want to just live with. Also a 2.5" lift and the issue was there with my original driveshaft and a new TW shaft. The original driveshaft needed to be rebuilt due to some cracked U-Joint boots and balanced and the cost worked out such that the TW was only a little more and I was doing alot of things with the Jeep so opted on the time saver.

The vibration first shows up at an axle speed of 3380 rpm getting pretty strong at 3800rpm and most shops can only balance to a speed of 3600 rpm. But because I've had this issue with multiple shafts, I'm not sure it's the shaft itself or a harmonic issue through the gearboxes. Running with no front driveshaft I get no vibration at speeds I'm really not comfortable driving this Jeep ~90mph.

I've always noticed the vibration is much worse if I'm in 4th gear and remember when the Rubicons first came out there were mentions in one of the early forums from many about some harmonic issues with 4th gear in the NV3550s, but never anything conclusive about why.

And there was also less vibration but not zero if I run no rear driveshaft.

I've been thinking about doing one of these https://www.balancemasters.com/driveshafts.html since it seems to be a bit of a hybrid thing. And since I lowered the speed at which it occurs with the 4.56s to a speed I'm often driving for extended periods on the interstates in my region I want to sort it out before I cause any wallowing in the transfer case outputs.