I have Vibrations on the highway (2.5 inch lift), I've diagnosed its coming from the driveshaft.

I have the proper angles for a conventional driveshaft, but they are still present. T Case drop didn't help either. Ready to go with an SYE, I called Tom's driveshafts to figure out the logistics and they heavily persuaded against a Hack N Tap. They say the vibrations are worse then with a proper SYE. But maybe they're biased because they have customers call them who botched the installation and say the driveshaft is at fault.

Realistically, If I go for the Hack N Tap and do it right, is it going to be worse than with a Proper SYE? I really don't feel like opening up the transfer case and starting that whole can of worms. I could always switch the hack n tap out if vibrations are still present after I get the custom driveshaft, assuming I can make the hack n tap the same length as what an SYE would be.

It's not my tires, its not my front suspension, its not my front drive shaft, my exhaust is not hitting the crossmember.I bought another balanced conventional driveshaft with new u joints and it was somehow even worse on the highway. I need a double cardan

 

Why not just do it right and go with SYE? These vehicles are basically becoming classics and flubbing your way into a solution as you've tried already with your transfer case drop is just going to cost you more time and monies.

Ditch the drop, switch to SYE, be happy.

 

Where do you feel the vibration? Hands, feet, butt in your seat.

Sye for a 2.5" lift is rather unnecessary and if that's the ultimate solution I'd argue your compensating for something else.

Are your leaf spring bolts tight, u bolts tight, does your rear axle have any pinion slop, are the locating tabs on the sides of your pinion yoke still there or has one/both broken off?

 

[QUOTE=

Sye for a 2.5" lift is rather unnecessary and if that's the ultimate solution I'd argue your compensating for something else./QUOTE]


I would have to agree with this. I have a 98 with a 3.5” lift and an 01 with 4”. Both have stock driveshafts with no transfer case drop and no vibrations.
Have you checked the play in transfer case output shaft?

 

[QUOTE=Offroadnutz;3729757]I disagree. I have a 92 with 3" lift and it would regularly eat u-joints every 5k to 6k miles.

 

Thanks. I will check those things, but:

Because I doubt myself whether an SYE is worth it to be it, I just put only my front driveshaft on and went on the highway 75MPH. I did not want to do this but this problem has been driving me nuts and I had to make sure. The whole time, it drove like what a 90s Jeep with 31s should drive like - not like a new car, but fine. Someone wouldn't get in the passenger seat and think "Wow this drives like ****". I thought maybe I was doing the whole placebo thing to myself, so I got off the highway, put my rear driveshaft back on, and instantly noticed the difference as soon as I gave it the gas to merge back onto the highway. On the highway it felt worse, in my seat, in the floor pans. I also gauged how much the lid of my console was vibrating when I placed my hand on on the first drive, and it was 2x worse. The clearest sign was how my glove box and console contents had been silent on the initial drive, but they were now back to their normal chattering from vibrations.

So that confirms it for me. I don't know why shimming didn't work(I used a gauge to confirm angles were good), I don't know why the t case drop only made a small difference, and I don't know why even a new driveshaft only made it worse. But there is no questioning it's at least drivetrain related.

I checked, there is no play in my T case output shaft, and it seems to be straight(See Video). My diff went bad a few years ago and I got the same one w/ correct gearing from a junkyard, (150k on it). The pinion does have some amount of rotational play in it,or "slop", but that is backlash right? Should I measure it? I also did have to re-tighten the pinion bolt when I swapped it, and went a little over the max torque to get the correct amount of preload. I don't remember if these vibrations were as bad before I swapped it out. I also don't think it has any locating tabs either, I googled it and couldn't find any photos of what they would look like.

All my rear suspension is about two years old, I have a shackle lift and I think that may be why it's harder to get the driveshaft angled correctly. Without shims, it is literally the perfect angle for an SYE. All bolts are tightened.

 

I bet ujoints are toast probly about 50,000 mikes ago.

The pinion is a rotating preload. Its not something you can just squash the nut down to a certain ft lb.

Rereading i see you bought another driveshaft so ujoints might be okay. After seeing you messed with the pinion i might start there. However im unsure if you have the ability to even get any additional tourge in that nut to screw it up.

What axle, 35 or 8.25?

 

Yes, and take note of the wear patterning on the ring gear and pinion while you're measuring the backlash

 

I have had the Hack N tap on mine for several years now, never had an issue with it.

 

Many folks don't understand that a typical driveshaft that has 2 regular "U-joints" is a Non constant shaft Unless the joints are at the exact same angle. If the output shaft of the transfer case is pointed downward 10 degrees from horizontal, the input shaft of the differential Must be pointed Upwards 10 degrees from horizontal, thus becoming a constant velocity shaft. If you install a double cardan joint, it can be at any angle, BUT, the opposite end of the shaft Must be pointed directly to the differential. Keep in mind that a single U-joint is a non constant joint.