Just finished installing new bushings, 5" greasable shackles , long travel bilsteins 10" rear and 12" front. I still have stock steering setup and a total of about 4" of lift right now. The problem I am having is that there is a vibration at the beginning of acceleration that goes away once momentum occurs. My truck is an 85 ext. cab 4x4, 22re, stock gearing, 31" tires (may change to 33" tires and 4.88 gearing). I am in the process of setting up for distance Australian type off-road trips (Moab). Long story short I am having trouble locating this vibration. I will be fabricating a new torque bar up front, and traction bar in the rear. The u-bolts don't move at all, and I checked the rear pinion seems good to me. I might add that the rear drive shaft is not perfectly in line with the transfer case but don't have anything to reference if this is correct or not. My truck did this before I added the latest parts I forgot to mention. Any suggestions will be greatly appreciated.

 

Unbolt the drive shafts and check the pinion nuts, also do the same for the mounting flange nuts on the transfer case, if they come loose it will cause a vibration. Have you ever checked the wheel bearings or trunion bearings in the front end ?.

 

I have done the wheel bearings, but I will have to check the trunion bearing tonight. Also rear pinion nut is good.

 

x2 on checking driveshaft bolts
If it did this before you added these parts, it sounds like the driveshaft isnt balanced. does it do it predictably within a certain speed window?

 

right at launch

 

what if you took off, and then took it out of gear? would it still vibrate?

 

I don't think it would because it doesn't vibrate in neutral.

 

well, that eliminates the driveshaft then. could be a throwout bearing or some clutch related issue.

Usually when its making noise on take off, its something with the rear end. did you make sure that you torqued the u bolts down to around 90 ft/lbs?

 

Check the u-joint phasing:
- http://www.4crawler.com/4x4/CheapTri....shtml#Phasing

And the shackles will affect your pinion angles:
- http://www.4crawler.com/4x4/CheapTri...l#Measurements
- http://www.4crawler.com/4x4/ForSale/...es.shtml#FAQ12

 

My pinion angles look pretty good today I jacked up the rear and let the tires spin. There was a slight wobble almost not even noticable. I have a strong suspicion that the leaves are causing it now, so with the installation of a traction bar the vibration may subside. I did not mention these leaves were on the truck when I bought it, so probably some cheap 3" rancho or the like. The only reason I kept them was that the arch was still good. Does anyone with a transfer case doubler or 4.7 recommend getting rid of the double cardin, and going with the single drive shaft and if so what should I look for as far as driveshafts? Another possibility could be the center bearing do these things go bad often I just replaced it a year ago and have put very few miles on it.

 

I also wanted to reiterate it only happens right at launch from stop and goes away quickly.

 

Just wanted to update on the prognoses, thanks Roger for the help, your website is great help. I decided to go with a one piece shaft and bypass the center bearing all together. I am really happy with this decision. I called Steve at south bay drive line and he made one for me the next day. By the way great guy to deal with when looking for any drive line parts. The truck feels like a brand new truck I am amazed that drive shafts can make such a huge mess with on road feel of a truck. To previous owner thanks for not marking the damn driveshaft for me!