My wife has our X Type 95% of the time so I only get to drive it when it needs something. This morning I was on the freeway to get it aligned and sure enough at 50 MPH there was the dreaded X Type rumble. At first I thought the new tires were off but after a few miles it seemed to quiet down but at 80 it howls. Never did it before, but what do I know, I hardly drive it. Okay so it's the driveshaft or is it? Can this be greased out or is a new driveshaft the only answer? Also I've noted the comment regarding rotating the driveshaft 180° as a potential cure but what is that doing and is that a long term fix or a band aid? And then some have had success after changing the transfer case fluid. We only have 70,000 miles on it. Where would you start? The cheap stuff right?
Thanks

 

Remember tires and wheel bearings usually harmonically act up at 50&70 mph and drive shafts about 3000 rpm, use different gears and speeds to trouble shoot most driveline problems at lest to get a starting place to separate front from rear and engine from drive line. sounds simple but it works.

 

It's the driveline, I've eliminated the other possibilities. So what is it about the driveshaft that causes them to require replacement?

 

Drive shafts themselves don't wear out it's usually the connecting joints. Say the U joint bearing or pinion bearing get worn to the point of say a thousands of a inch or what ever it causes a RUN-OUT or eccentric pattern from true center then the weight of the shaft is thrown from side to side causing a vibration and at different speeds and becomes HARMONIC in relation to the speed (rpm) of the shaft. Where i used to work they balanced large and small blowers at certain speeds because the vibration showed up at thoughs speeds. Spin a shaft with no run-out and it doesn't have any weight but add run-out or weight to one side and the weight of the shaft multiplies very fast called G force like on a centrifuge or a merry-go-round.

 

Check out Harmonic Balancers or counter balancers for a engine so the crank shaft doesn't tear the engine apart

 

I am most familiar with the typical drive shaft U joint arrangment and what a bad U joint feels like. I was just caught a little off guard that instead of replacing a wonky U joint you have to buy a whole new driveshaft for $500.

If applying grease to the carrier bearing as some have indicated (if that's even possible) quiets it down is that a long term fix or a band aid?