Nasty vibration when transfer case is in neutral.

This jeep has had a tow bar on it most of its life and only owning it for the last couple of years I don't know a lot of the mechanical history but I have towed it short distances across town several times in the last couple of years without any issues leaving the driveshaft in the jeep. I noticed the last time it was hooked up I could feel a patterned vibration in the tow vehicle (like a card in bike spokes). During inspection I found both inner and outer pinion bearings in the jeep were toast. I have completely replaced the rear end with a flanged find (until a FF unit is finished) and figured that that was the cause but the vibration its still there. I had my wife pull me around the block with me in the jeep . Clutch in or out trans in gear or out OD in or out, still there! So I unhook the jeep and drive it no vibration find a hill and shut the engine down and coast with the clutch in or trans out of gear and OD both directions no vibration.

My next attempt is to pull the drive shaft and see what happens.

My question is this TC supposedly has the 3.15:1 gear set installed and could a bad intermediate shaft or some other bearing be the cause? This a good place to start?

 

Checked all the driveshaft UJ's and splined slip joints? Knuckle UJs?

 

I'm betting driveshaft u-joint(s).

 

Yes, I failed to mention that I replaced both joints while I did the rear end swap. Also the slip yoke is good and tight.

 

I have lock outs on the front and have them disengaged but have not pulled the front knuckles down to inspect the axle joints, That is on the list to check just because it needs to be done.

 

Did you check to make sure the lockouts are actually unlocking?

 

How are your wheel bearings?

 

I would be looking to see if the tow system is tweaking something.

 

Are we 100% positive it isn't the tow vehicle?

 

What about U-joint angles? Is the slip yoke moving freely?

And I agree, look at the tow bar and equipment and I'd be looking at the tow vehicle carefully also. The extra load could be causing a problem to show up that isn't apparent with no load.

 

U-joints out of phase, maybe, if the slip yoke was dismantled?

 

I thought the same thing so I hooked the jeep up to a different tow vehicle and rode along in the cj as the wife towed me around the neighborhood and the noise and vibration is still there. The slip joint was never pulled apart and is tight without slop but will slide with ease, I have swapped the front and rear joints on the rear shaft with no difference than before I swapped the rear end. I pulled the shaft and the problem goes away. So I will replace with a known good shaft that is under my 71.
As for drive shaft angles, nothing has changed suspension wise over the several thousand miles i've put on it since I have owned it. But that is something that I do need to investigate further. It has a set of 2.5" springs under it and what I believe are the correct wedges are in place.


What has me puzzled is I can hop in it and drive it 55mph and no vibration or noise. I would think I would be able to able to feel the and hear the same vibration i hear while riding in it when its being towed.

 

Rear end has new ones, the previous rear had a couple thousand miles on them. The fronts have a couple of thousand miles on them. The front dif has a tight power loc in it so I can tell when the hubs are engaged. I do need to verify if they are completely disengaging though...

 

Check the front hubs for disengagement like you plan. Also, what is your front caster angle? I've seen vehicles drive "ok" with certain caster angles but not tow worth beans.

 

What if you are coasting downhill?
Things like differential ring and pinion gears can act very different under load versus under drag, if they are out of adjustment.