I start getting a vibration at about 45 mph. I lowered the rear 1.5" to see if maybe the drivetrain was too out of angle, but it still vibrates the same. It kind of levels out at about 65mph, or maybe it just vibrates so much that it does not feel so strong. At 45 you can really feel the whole thing vibrate underneath. The steering wheel is fine, so it is not aligement. It could be the diff. I already replaced it about two years ago, but it does not vibrate below 45. Some other people had complained about a similar situation, can anybody tell me what they found.

Been through any ice/mud????

Wheels out of balance, mud behind the rim, lost a balance weight????

Still could be a loose wheel bearing, or a shot idler arm bushing in the steering.

Can you nail it down to one end or one corner?

How about a drive shaft universal joint?

my first guess.....

The universal joints are new. When they go bad they usually whine or squeak. I thought of the drive shaft balancer, could be out of balance, but it would vibrate above 45 and the vibration is not as bad from 50 to about 65 and it gets bad again at 70. No mud on the tires, the front drive unit is all new.

ok, sometimes if the u-joints are out of phase or if the t-case angle is different than the pinion angle, it will vibrate. check those.

most obvious though is tire balance.

Only way to make the u-joints go out of phase is to disassemble the driveshaft at the splines. Not something that you normally would need to do.... There is no way of suddenly making them "jump out of phase", it is an assembly issue.

If the problem has developed without doing anything to alter the vehicle in any way then it is not a reassembly issue (out of phase u-joint). If the vehicle does not exhibit the same symptoms throughout the speed range, then it is unlikely to be something that is actually broken. If the vehicle only develops the symptoms at a particular speed (range) then it would most likely be a balance issue (tyres/driveshaft balance), or a mechanical resonance/balance issue (idler arm bushing, bad u-joint causing driveshaft vibrations, loose wheelbearing with a bit of "caster shimmy" [ie, "shopping trolly syndrome"]).

That's the logic behind my thinking.....

well, i guess some of us do that more often than others......