This has me stumped so far. Something is causing a rhythmic tug to the right in the steering. It's very noticeable below 30mph and smooths out above that. It seems to move in sync with the wheel rotation. The tug is strong enough that the vehicle visibly rocks with the pulsation.

I've checked both the front and rear brakes on both sides (there was a small leak in the rear axle seal which I repaired) and I've examined the tires for anything obvious like a bubble or tread separation. So far, I've come up empty. The tug is getting worse with time to the point that I don't want to drive it for fear something bad is going to happen. It acts like a rim is severely bent, but I haven't hit anything and turning the wheels by hand looks normal.

Any ideas?

 

You might have a CV joint binding.

 

That would apply if you have the ADD front axle where the CVs are spinning all the time. I had a CV joint on a VW and it had a once per wheel rev. twitch in the steering that would pop up from time to time. Put the front wheels in the air and give each one a spin and watch the CVs and feel the stub axle while it turns and see. Also, check the surface of the tire while it spins, I've also have a tire with a flat spot and one with a broken belt do the same. Hold a pointer of some sort up to the tread as it spins and see if there is any movement side-side or in-out on the tread.

 

try swapping the front tires for each other. see if the tug is now to the left or has stopped. there may be a problem with the tire you can't see.

 

I have the same thing going on with a car right now. Turned out to be a belt going bad in the tire. It gets worse when the tire heats up during highway driving.

 

I have manual hubs and they are unlocked, so I don't think it's a CV joint.

I tried rotating the tires on the right side front to back and it didn't seem to make much difference. Tomorrow I'll try swapping right and left to see if the problem changes sides. I suspect it's a tire, but I didn't see any defects when I had them off.

 

When was the last time you re-packed the wheel bearings? It could be a bent cage or bad roller.

 

I checked the wheel bearings when I had the calipers off. They turn smoothly. They only have 10K miles on them.

 

Found it. Even though the truck was tugging right, the problem was tread separation on the left front. The area of separation was so large that it blended in making it hard to see. I saw it by accident when the light hit it just right. I put the spare on that spot and the problem is gone. Woot!

The bad news is that it looks like I need another set of tires. $$$