This started 100 miles from home today:

It doesn't seem to happen while coasting down hill.
I've crawled under and given the front prop shaft a shake, but it seems solid.

I know I need to replace a serpentine belt, but the sound only happens when the vehicle is moving and accelerating (which makes me think it's not the belt).

I was able to get it back home, but I'd like to not knock a hole in my transmission if the shaft fails.

Thoughts?

 

No thoughts. I know what it is. It is your driveshaft. 100 percent sure. You need to get that one serviced or a new one. If it is greasable you might try filling it up.

I've been through 3 (I have a lift). I'm positive. Sound is unmistakable.

If you have a locking cdl you can take off the front driveshaft, lock the cdl, and drive around the block on the back one only. You won't hear a squeak.

 

Well, crap.

Ordered a new drive shaft. Should be here on Friday.

 

I've tried thinking past a driveshaft (no sound while coasting, worse at certain speeds, goes away, wondering about belt and pulleys) too. You saved a lot of time by posting a video and just biting the bullet and ordering one. I would have dithered over it, considered having mine rebuilt, googled rebuilding, checked 15 sources for the cheapest price for a new one, etc. Then, at a point when delivery would cost twice as much or skip over a weekend, I would have ordered. It's a pattern. Ugh.

 

I heard that sound start, and immediately thought "Well, I guess I know what I'm doing with my Friday night." I'm just glad I made it home without something flying loose down there. A drive shaft I can replace, but a transmission is more than I have capacity to tackle.

While I'm at it, I guess it'll be a good time to get the diff guards I've had sitting around installed.

 

Yep; if you are going to have to crawl around under your truck, DO IT ALL!

When you get the driveshaft off, try completely articulating the double cardan end... I am curious whether that was a U joint or the centering ball. I had two go bad with U joints, but the third (which was a rehash of the second, I think, after new U joints...I've lost track) was the centering ball. I didn't even know how to grease a centering ball so, um, it obviously suffered from a lack of attention.

 

I got it swapped out, but didn't have the energy to go poking about the old one. Squeaking is gone, and it's driving just fine now. I'll take a closer look later this week.

I'm planning on rebuilding the original shaft for a spare, but that depends on what I find. I suspect it's the centering ball, or one/both of the double cardan.

 

Congratulations on fixing it. And, again, for not wasting time like I would have done.

When my centering ball was bad it squeaked pretty good just in my hands, bending the double cardan around. It was bizarre.

I believe Cu

 

Congratulations on fixing it. And, again, for not wasting time like I would have done.

When my centering ball was bad it squeaked pretty good just in my hands, bending the double cardan around. It was bizarre because I was expecting a bad u joint and they were all fine. I was told that I should have greased it as part of regular maintenance. I had no idea how to (and still don't) but someone said if you remove the shaft and bend it to the maximum you will see a small hole at the periphery of the centering ball that will accept a grease needle. ... which, if true, explains why I have never greased one

 

Before I knew about Discos and prop shafts, wife's DII was squeaking for a couple weeks. Finally I looked and saw 1 U-joint just rusted apart - like only 2 caps intact. She was driving on it a while. Drove it to repair shop and replaced the 1 single U-joint.

2 years later I learned about the prop shaft, and out of shear and utter fear of a tranny explosion, I bought a Lucky 8 shaft and replaced it because I was told if I don't have "4 grease fittings, replace it before it explodes". Literally the post was "4 grease fittings - period". Do it.

My shaft had 3 fittings - no fitting on the slide collar shaft. Crap! Because 3 does not equal 4, I had to swap it, I thought.

Then, when I got my wits about myself I dug through the paper work and saw a receipt where my brother-in-law actually had the shaft rebuilt with new U-joints and grease fittings on all U-joints. The 4th fitting that was missing, was one that is usually removed and capped, then you insert it only when greasing.

So, to be safe, I had a new shaft installed, $200 peace of mind, when there was no real emergency. Basically I read so many posts I confused myself and had myself thinking the weak point was my shaft was missing a grease fitting at the collar and THAT was the one where things break. Wrong. Had I understood that as long as EACH U-JOINT has a grease fitting, and they got greased regularly - life is fine.

Anyway, my lesson learned.