2004 Disco with 85K miles, previous owner(s) didn't really take care of it but have got the truck up to snuff minus a vibration at 70-75 mph. I know that you're not supposed to drive that fast but locally you could be run off the road if you're not going that fast. Here's the rundown on what's been replaced/fixed-

1. Front driveshaft was rebuilt with centering ball, supposedly balanced by driveline shop (weights can be seen on the shaft); no change.
2. Tires have been replaced, no change. Wheels appear to be straight.
3. Rotoflex has been replaced, no change.
4. Fluids have been exchanged, no change.
5. Suspension coils and shocks have been replaced, no change.
6. Brake rotors and pads have been replaced, no change. Didnt think this would help but thought I would mention it.
7. Last weekend I replaced the front xfer case output flange and seal, the nylock nut was barely hand tight and the splines on the original flange looked very worn compared to the new flange.

So, after installing the new flange the vibration at 70 is still there, doesn't matter if it's on or off throttle or if it's in drive or neutral. A new vibration exists from 35-40 mph, not as noticeable as the 70 mph vibration but if you're off throttle it goes away, get back on the throttle and it's there.

The vibration can be felt through the seat bottom and is more of a rumble, sorry for the novel but want to lay it all out there. Does it sound like a driveshaft issue or am I missing something? I'm tired of throwing parts at this thing and want to get it sorted once and for all...

Any thoughts are greatly appreciated, thanks!
Andrew

 

ball joints, bearings, axle links,.. heck anything can be causing it. you are assuming it's the driveline, but im looking at suspension parts. something it is just the road itself. few stretches here will produce universal vibes in any vehicle. something to be aware of.

and i cruise at 80 with 33s all day long so cant imagine why you arent supposed to go 70.....

 

One thing about tire balance, if, as an example, it were out of balance, double that speed and it will be out of balance there also, like 35 and 70 MPH. Go get yours rebalance.
If still there, remove the front drive shaft and see if it goes away.

 

I know the tires are balanced with no problems, I've had those checked already. Funny thing is I pulled the front driveshaft this weekend and tried to go for a drive until I remembered I forgot to lock the CDL, I crawled under but couldn't see anything on the passenger side for a 10mm wrench. Does the '04 have this or have I completely missed something?

After driving yesterday I noticed a few drops on the driveway and it looks like I need to replace the transfer case seal again, maybe I cut the lip when I put the new flange on (dry just like RAVE says to do), has anyone had any issues with this?

The 35-40 mph vibration didnt start until I put the new flange on, nothing else has changed so i'm wondering if its the front shaft? Anyone have a picture showing where the transfer case lock is located?

 

The '04 has the CDL shifter in the cabin.