45-50mph vibration

Jack up the front end and spin the tires as fast as you can and watch to see if the tire is running up and down too, or out of round. You may have a wheel that isn't properly centered on the hub and spinning slightly off center, this would explain why swapping with your friends tires didn't help, his rims are off centered on your hub too.

 

Alignments will not fix shimmy's or wobbles or shakes, that is something out of balance or out of round.

 

+1 what the above guys said. something is out of round or out of balance, a wheel not centered on the hub or tires out of round.

 

I recently had this problem on my freightliner it was a bent rim

 

I had a vibration in my fld it turned out to be the front shackle pins were seizing up replaced the shackle pins and bushings with easy rider roller pin bushings man the ride improved and no more front vibration's. when you pull your shackle pins look them over for flat spots and rust. hope this helps.

 

I have seen out of balance driveshafts do this, at this speed, over time the shafts will distort ever slightly and just need to be rebalanced. just a shot in the dark, has helped me out a couple times with heavy haulers with higher (over 500k) mileage

 

It depends how the steering wheel is shaking, usually if the steering wheel is rapidly turning slightly left, right, left right, and so on the problem is most likely with the steer wheels. Something like the drive shaft out of balance can cause a shake in the wheel and most certainly the hood too, but the shake felt in the steering isn't really a side to side shimmy. Tires spin about 4 times slower than a driveshaft so tire problems are usually felt as a shimmy or shake, drive shaft issues can be felt more like a buzz or fast vibration. It is hard to express these sensations on forums like this.