72-79 MPH vibration 2008 LZT

[Miataracer]

New member here...

My 68K 2008 LZT has developed a high frequency vibration that occurs between 72 and 79 MPH and which is accompanied by a "rumbling" which is at the same frequency and that can be felt (and ever so slightly heard). The vibration is not present below or above that speed.

Until last week it did not exist and in fact it was not present when I came off the expressway Saturday morning but was immediately present when left my destination and came back to highway speed on the way home later that day.

Since the OEM 275/55/20 Silverstone tires were readey to be replaced, I had new ones installed but there was no change. Suspecting a lost drive shaft weight, I put the car on the lift but none are missing.

The only thing I can find is that the LR wheel bearing has the slightest play when I rock the wheel top to bottom. Before I take it into the shop and have them replace the bearing, I figured I'd ask here to see if anyone has had a similar problem - and if so what they did to cure it.
Rick

 

[Metaldrgn]

It would seem that 70+ mph is the magic number for vibration if your vehicle is going to vibrate. I've owned multiple vehicles in the past that did it and I've seen numerous vibration dampers on later model vehicles I believe were added to try and combat this. There are many reasons it could happen. You could try rebalancing your wheels. Your transmission mount bushing may be worn. I've even read that the driveline angle on certain years of expeditions can cause this.

 

[Miataracer]

As promised checking in after getting it back from the shop. The rear U joint was frozen. While it was rapidly moving toward total failure, there was no play in it! Upon removal and dismantling, one of the four yokes was so devoid of grease that it was corroded to a dark rusty brown and the needle bearings in the cap were in the process of disentegrating.
I guess is the the takeaway here is "look" at the U joints, versus the typical external exam where you look for play in the joint if you have this sort of of vibration.
Rick

 

[Metaldrgn]

Glad you figured it out!