SOLVED Odd shaking initial drive

[ukrkoz]

07 Tahoe LT
Developed weird shake in the morning.
After I start and take off, drives fine until I reach arterial, which is about thousand feet away. On arterial, it has strong shake for about quarter mile.
My entire left leg and buttock shakes vigorously up down.
After quarter mile, shake disappears and truck drivers fine.
The colder outside, the worth it gets. Truck is parked outside.
Definitely not the road as scooting across tarmack or even into the incoming lane doesn't change anything.
When it's hot outside, no shake.
Tires are only about 7 months old.
Rear air shocks aftermarket. Airbags work fine.
Any ideas? Far I know, shake in the floor and buttocks points at the rest end. No shake in steering or dash.

 

[B-train]

Couple thoughts:

1. Tire malfunction - shifted belt or other. Have them road force balanced. You could also move the backs straight to the front and see if the vibration follows. You can also try watching rhe tread pattern in dust, or when wet, on a hard smooth surface to see if anything weird shows up in 1 revolution

2. U-joint that is tight and loosens up with some movement. Drop driveshaft and inspect both joints for free movement. If there's any sticky or tough areas in the range of motion then replace.

 

[OR VietVet]

I am going with #2 by @B-train

Could be tire related too but still think is u-joint based off of the vibes explanation.

 

[ukrkoz]

Thank you
I'll move tire. It does kinda feel like bump in tire that goes away as tire warms up.
I had cheap shock once that did similar.

 

[ukrkoz]

You mean - the differential side u joint?
Zero noises.

 

[OR VietVet]

Not the front, the rear driveline.

 

[ukrkoz]

Yes, of course. Ass shakes.

 

[OR VietVet]

Ass shakes typically means a rear driveline problem. May be the spline back there that is hanging up.

 

[ukrkoz]

It lasts only about 15 seconds at 40. That's what beat me. And after work drove like butter.
It's only in the morning and only when cold.

 

[Geotrash]

It lasts only about 15 seconds at 40. That's what beat me. And after work drove like butter.
It's only in the morning and only when cold.

And is the shake/vibration at the frequency of wheel rotation or driveshaft rotation (3.x times wheel rotation speed)? If it's at wheel rotation speed, I vote either broken belt/cord in one of the rear tires, or a bad/damaged wheel hub. Are you running any wheel spacers, by chance?