Rhymthic Vibrations on the Highway

I'm got mild rhymthic vibes at highway speed (noticeable around 40 mph, and then disappearing until around 65mph - it's not really noticeable from 50-60 and 70+). The hum and vibration lasts for a second or so, and then goes away for about as long before coming back. I don't hear or feel it, when my foot's off the pedal, which leads me to believe that it's the driveshaft.

The truck's lifted a few inches in the rear (Stage III Deavers), and I already have the a 3/8" OME spacer dropping the carrier bearing. The ECGS bushing is also installed. I don't have angled shims on the axle. The U-joints get greased whenever I change the oil. The rear driveshaft has gotten scratches a bit on boulders, but it looks straight and the doesn't seem like much was taken off the shaft besides the finish.

I do have a used spare driveshaft that looks to be in good condition. For reference, I'm also presuming that this would be the replacement part for a 2011 V6 access cab? https://autoparts.toyota.com/products/product/shaft-assy-propeller-w-ctr-bearing-3710004352

Opinions and suggestions on what to do in the short and long term?

 

Drive shaft unbalanced?
Wheels need balancing? (Lost a wheel weight a week ago caused vibrations)

 

What about a bad wheel bearing? Does it do it when turning a corner at the 40mph range you’re getting the vibration at?

 

Put the truck in gear and turn the engine off.

Get under there and try to spin the driveshafts. You are looking for play from worn u-joints.

If one wheel bearing is loose, you will notice it more while turning to one side.

You could use angled shims under the leafs.

 

Thanks! I'm planning on getting a road force balance done (to verify it's not the wheels/tires), and will some more testing to check if it's the shaft, U-joints, or wheel bearings. I'll probably will order up the shims regardless, given the amount of lift on the truck.

One other thing: How much play should the driveshaft have at the carrier bearing? I was under the truck yesterday, and it seemed like it was very easy to move around compared to what I expected.

 

Haven't had a chance to get the wheels rebalanced or drive it again, but I got back under the truck, and checked the U-joints and driveshaft and pinion angles. The U-joints all seemed fine. If I'm understanding things correctly based on this video, I think a 3-degree shim on the rear axle should hopefully do it.

Forward Driveshaft Inclination = 7 Degrees
Aft Driveshaft Inclination = 8 Degrees
Pinion Inclination = 4 Degrees
Fore-Aft Difference = 1 Degree
Aft-Pinion Difference = 4 Degrees

https://www.youtube.com/watch?v=f1m-Fh5kiRU

 

My left front wheel bearing died. The sound you describe is text book for what I experienced. Got worse and worse until it was just a loud hum in the cab. I think this forum is the reason I figured it out. Died early around 45K miles. Correct me if I am wrong but if you jack up the truck you would be able to feel the play in the wheel if its a bad bearing.

 

my wife’s jeep had a rhythmic sound coming from the front at highway speeds only turning left and we took it to dodge and it was a bad wheel bearing so that could be it too… they replaced the wheel bearing assembly and it’s gone now.

 

Update: The front wheel bearings are fine. I added 3-degree shims over the weekend, and the vibrations are now only noticeable from about 57-62mph on the speedo. After comparing how much my carrier bearing can be manipulated by hand to @El Taco Diablo's, I'm pretty sure that that's the culprit, because it just seems loose.