Need some help confirming my theory here before I dig into this...
4wd truck with cv axles and sealed hub units. Has what sounds like a bearing howl in the front end. The howl stays on right-hand turns but disappears on left-hand turns. Which bearing is bad?
(I see this as a "bearing issue" as opposed to a "truck issue" so I put it here.)

The one that is howling? My Bad, just being a smart...as$

I would think the passenger side! but if you are going to replace one side you may as well do both.

I would tend to think it is the left hand (drivers side) hub making the noise because in the right hand turns the left hub is moving more. But, unless money is an issue, I would do the left first and then the right because it is going to go next.

If noisy on RH turns, it is the left side which needs replacement.

Most times it is the opposite side bearing from the direction the vehicle is being turned. But not 100%, I've been burned before by that. If the truck has front coil springs jack the front end off the ground. Rotate the wheel with one hand while grasping the coil spring with the other hand. The coil spring will resonate in on the side with the bad bearing.
Doug

My original post should've said "before I dig into this again". I've already replaced the side I thought was bad...I thought wrong.

The hubs are $130 each. In this instance I'd have preferred to only replace the bad part but that ship has sailed. This is now a poll of sorts (to help my ego if others felt the same one was wrong as I did) and a learning experience for others to avoid my fate.

The coil spring test is a good idea. Unfortunately this has torsion bars. I did jack it up and spin the wheels first. The side I replaced made only a slight bit of noise. Neither side had slop when wiggling the tire at 12 and 6.

Many are loose also.Jack it up and see if the wheel moves.replaced a lot at work especially GMs.The cheap bearings dont seem to last so get a quality one.We used mostly Advanced.I believe they were Timkens.Rocky

My rule of thumb. When working on suspensions, both sides of vehicle are treated to same repair. Period.

You are spending unnecessary money. Mileage and age are often kind to front end parts. My 64 Belvedere drag car needed only bushings. My 198,000 D350 has only needed 2 lower balljoints, My 73 Challenger one lower ball joint and bushings. I spent 27 years as a dealer tech specializing in chassis, axle, suspension.
Doug

Typically, On a right hand turn the Left bearing would get more load as the weight is being shifted to the LF wheel. there can be other parts that CAN complicate the root cause, IE: Calipers, pads, wheels, CV joints, u joints (4WD) and even tires.

jack up the front and use stands to support both sides. have a helper put it in drive and get it up to 30-40 mph or wherever the noise is audible. Sometimes you can hear the noise if you listen with your ear right next to the spinning front wheel. Try both sides and compare. If you can't tell then use a long screwdriver (a thin one is best) and place the end on the steering knuckle(as you lay under the truck)and listen with your ear on the handle end. Again try both sides and compare for the louder noise.

Some that I wasn't sure of which side it was? put it on a lift stop one wheel from spinning by setting it down on an old rim and putting it in gear and slowly give it gas.

I replaced the right one on my Ram.

The left one failed within 9 months and almost left me stranded.

Chnged the right one on the Focus in August. The left one is noisy now.

Change them both

I know what you mean Doug as I have been fooled before on that. I always put the car in the air and run the wheels while putting my mechanics ears up to each hub and I can usually tell very easy for sure like that. Ron

I used to be pretty good at figuring out which side bearing was making the racket, and sometimes even guessed if it was the inner or outer bearing on the noisey side. Always have to make sure there's no heavy cupped tires first too. Sounds like you'll be changing them both anyway, at this point no?

Well I was in the same boat as many here. I thought that the bad bearing would get quiet when "unloaded" going around a turn. In this instance it was just the opposite. The bearing went quiet when more pressure was put on it during a turn. This seems counter-intuitive to me but "them's the facts"...in this case.

As for some of the other comments:
-This was an auction purchase with new tires. No known history. Maybe other hub would go bad soon, maybe it was changed a year ago.
-It wasn't my money I was spending. I was helping somebody else. We gambled on what seemed like logical troubleshooting and lost. So be it. Hopefully somebody else can learn from it.

the old "turning while driving test" worked well with cup and cone style bearings..... the newer sealed ones, not so much. You pretty much go opposite of what you knew for so many years. I just went through this on my Jeep Cherokee.... but being it's a 96 with 160 K on it, it got both.

Interesting information. Thanks for sharing the knowledge