I'm going to start today, I'm going to jack up all 4 wheels and run it while the wheels are off the ground, I hope the noise persists.

It started with an impulse buy for a truck with a lot of miles, decent body, rust free/solid frame, but it has issues. The first issue I noticed was the loud noise from seemingly the front/left, I'm hoping it's a wheel bearing, but fear it's a broken diff or transfer case. Previous owner said "it has a problem in the front driver side wheel and a leaking rear/left wheel cylinder", but it has more problems than that, I fear. I first pulled the tire/drum to check the rear/left brakes... one pad was spun 90 degrees, broken spring and retaining pins, shoes were worn to the rivets and the drum was gouged... replaced and the brakes seem good now, but the loud, scary noise in the front is next. I've yet to move the stick from 2 wheel drive into 4wd and see what happens. I suppose I should try it and see what happens? Front drive shaft was removed by previous owner.

 

Is it possible the brakes were so "out of balance" that the... proportioning valve? Or other brake component is setting off the ABS pump and causing the nasty sound? The rear/left brake cylinder was essentially pushed out until it pretty much was exploded.

 

ABS sound isn't that loud.

 

How many miles on it?

With the front jacked up, spin the left front wheel by hand. Noise? Feel crunchy? Rough? Wheel bearings can make some rude noises, and they aren't all that bad to change.

 

Like 250k miles, but I don't know what the drivetrain actually has, just to odometer. I've spun the front tires by hand, no noise, no play top-to-bottom when shaking the tires. Going to post a video here later today of the truck running with all 4 wheels jacked up, maybe someone can identify the sound. Thanks for the comment : )

Edit: Just realized, I don't have my front drive shaft installed, lol. So likely won't find anything as the front tires won't be driven... I'll see if I can install the front drive shaft, but if I recall correctly, previous owner snapped at least 1 bolt removing the front drive shaft, but I'll have to double check. Will post a video later.

 

Front axle u joints are pretty common, I usually spin front diff pinion easily back and forth and it will show bad u joint very clearly.

wheel bearing, spin the tire and hold the coil spring. Lots of bad wheel bearings won’t have play, this trick helps greatly finding which is bad. I work in a shop and deal with this all the time and you’ll feel the bad bearing radiate through spring, works on every vehicle with a coil spring

also is the vacuum to 4x4 damaged and it’s partially engaged?

 

I didn't even consider the 4x4 being partially engaged, lol, thank you, that may be it. The sound is not consistent, and it's a loud nasty sound, unlikely a wheel bearing, Here is a video of a Chevy making *almost* the exact same sound at 5:35 (his turned out to be a loose parking brake cable and my parking brake cable is also loose, so I'm hoping it's just that, but it's a scary sound while driving):

 

Unfortunately that sounds like mine when transfer case crapped out…anything above 25mph it would grind….

 

X2! Might want to inspect/remove the cad unit and see if that could be causing it. Also did you remove the fill plug on the axle and see if it has gear lube?

 

I have not checked for gear lube, but will, thank you. I jacked it up, messed with the 4wd shifter, and it grinds going into 4wd (all 4 wheels off the ground and in Neutral), not sure what that means; also, the front/left wheel *does* seem to have some play up/down, so possible wheel bearing is needed too.