Help diagnose a shake / vibration at 72-77 mph

[2002_thundercloud]

Hey Guys,

I've searched till I can search no more... I need some help diagnosing a throttle-on vibration that occurs right between 72-77 mph while crusing on the freeway. At 70 it's smooth and by 80 it has smoothed back out completely. Between 72-77, I can lift off the throttle and the vibration seems to goes away, mostly. The frequency is low and feels just like a tire that is out of balance. I have brand new Michellin X LT2 265/70R16 on it with less than 5,000 miles. I had them balanced a second time just last week before our 900 mile run this past weekend and the tech said they relocated the weights just slightly on the left two tires... but it did nothing for the vibration so I had to run either 70 or 80, mid 70's were too annoying. I suppose it's possible they still didn't get the tires right. And this could be my imagination, but it seems more pronounced in the afternoon of the last few days since it's been in the 90's here. It's a 2002 4WD Limited with 83,000 miles. It's never been off road or road hard. Thanks for your help.

 

[JohnsD90]

Probably your rear U joint on the driveshaft, but try to grease all 3, but the one that doesnt take grease is likely the one causing the problem, if not U joints get your tires balanced, because it could be that, and even if you just got them balanced they could still be the problem. But i suspected U joints.

 

[fusedapart]

I had the same problem, and I asked them to re-balance the tires... no luck. They said that they thought I could fix it by just rotating, (not balancing them) and oddly enough it worked for probably a few thousand miles... (i drive it hard off road)

Make sure you don't need an alignment and try rotating the tires?