Help Tracking down intermittent shaking

I've gathered a steer axle tow out causes a vibration starting somewhere around 45-55 mph and goes away about 10 mph faster than when it shows. I've heard steer axle kingpins with worn shims contribute as well. Gathered all of this from MD Alignment. Important to make sure 1/16'" tow in by sipe measure after driving the truck forward before stopping and measuring. And it is also important to jack the steer axle before lubing the kingpins, and then turn the steering wheel both directions as far as you can. Hope this solves your problem some.

 

Hanger bearing.

 

I do not see how those things would change when you hit a bump?

 

I had a problem that changed with hitting railroad tracks and such. The tires had a powder type balancing compound in them. Moisture from the air caused the compound to clump together and cause vibration. If stopped it would spread out evenly until some hard bumps were encountered.
Did not even know it was in the tires. Spent a good bit of money for someone else to to teach me that.

 

It was 10 years ago when I used to listen to Mike Beckett on the radio. If I remember right, the forward rotational force is working against the tow out (there is is always some play-should be 1/32" max at all related parts - tie rod ends, drag link-for a total of 1/16", which is why tow in is that amount). And at some point they reach an equal force, causing a vibration if towed out, until you drive through it until you speed thru it. I used to always have a vibration until I started doing my own alignments and changed kingpins. I'm just guessing hitting bumps might be effecting those competing forces.

 

MRMTRANS is making an excellent point.
Some string, duct tape, a pen and a measuring tape is all you need to confirm if it’s toed out. Should be towed in 1/16-1/8”

 

If you feel it in the seat and not the steering wheel the problem is going to be in the rear. I would check the torque rod bushings. U bolts, tires for roundnesses.

 

How long does it stop for after you hot a bump?