Shake when truck is cold

[Ian Mills]

When the truck is cold first thing in the morning (air temp ~35) it has a wicked shake at 24 mph and 48 mph. It feels like one of the back tires is flatspotted or out of round. However, after I drive a mile or two the issue goes away. At first I thought I was just imagining it but the back of the truck is definitely doing something funky at those particular speeds. Any ideas would be much appreciated.

The tires have been on the truck since October and this issue is new in the last few weeks.

[swathdiver]

1 hour ago, Ian Mills said:

When the truck is cold first thing in the morning (air temp ~35) it has a wicked shake at 24 mph and 48 mph. It feels like one of the back tires is flatspotted or out of round. However, after I drive a mile or two the issue goes away. At first I thought I was just imagining it but the back of the truck is definitely doing something funky at those particular speeds. Any ideas would be much appreciated.

The tires have been on the truck since October and this issue is new in the last few weeks.

Are the tires LTs?  Has the sun been shining on the tire closest to it for a while right before you get in?

 

My home faces east so the left side tires get the most sun as the truck faces west.  It takes a little while for them all to heat up and even out, about 5 minutes or so depending on the weather, then they are smooth as silk.  

[Ian Mills]

Yeah, they're big ole load E tires.

The back of my truck faces the same way as yours I think based on your description and yeah, the sun is up and on the tires when before I head to work. I'll try backing in tonight and see if that makes a difference.

That's such a weird problem

[Ian Mills]

I backed in last night so the front/right tires were seeing light instead of back/left. The shaking felt the same.

[swathdiver]

Well, have you had a look a the sway bar bushings in the front and rear?  Checked over the bushings in the control arms on both ends too?  Ball joints?

 

At twelve years old my control arms bushings have some dry rot and am replacing them now.  Replaced the sway bar end links last year as they had rotted and fallen away.

 

Generally speaking, rhythmic shaking at certain speeds is driveline related, the tires may need re-balancing or a caliper might be sticking and or something is amiss with the differentials or shafts like the u-joints.  If you feel it in the steering wheel, it's usually up front and feeling it in the seat means back aft most of the time.

[Ian Mills]

11 minutes ago, swathdiver said:

Well, have you had a look a the sway bar bushings in the front and rear?  Checked over the bushings in the control arms on both ends too?  Ball joints?

 

At twelve years old my control arms bushings have some dry rot and am replacing them now.  Replaced the sway bar end links last year as they had rotted and fallen away.

 

Generally speaking, rhythmic shaking at certain speeds is driveline related, the tires may need re-balancing or a caliper might be sticking and or something is amiss with the differentials or shafts like the u-joints.  If you feel it in the steering wheel, it's usually up front and feeling it in the seat means back aft most of the time.

I did an all-new front end in January, that all looks good still. 

I agree that it feels like driveline and I feel it in the seat which is why I suspect rear. However, it's weird to me that it goes away after a mile or two.

I checked the back tires and rebalanced them last week. They were out of balance but the problem is still here after I fixed it.

I'm due for a tire rotation in a couple hundred miles (I rotate every 5000) so I am interested to see what that does for this issue.

However, if anyone ese has any ideas, I'm happy to listen

[Ian Mills]

I rotated the tires on Sunday afternoon and the problem is largely gone. I have no idea what was going on but it's fixed for now.