Rattle, mid-truck
 

97 F-Superduty started to have a rattle out of nowhere. Rattle doesn't start until I've passed about 40MPH, and it will continue until I have stopped. It is speed related, not RPM. Sound is consistent in neutral, with brakes applied, and parking brake pressed. Rear diff fluid is full and clean. My next assumption was the driveshaft carrier bearing. Any thoughts?

ZF5, 4x2 dually, Cab and Chassis frame

Another possibility is the U-joints starting to go bad. Park the truck on a level surface and chock the wheels. Place the tr4anny in neutral, and get under the truck and try to wiggle the drive shaft, and inspect the u-joints for signs of rust coming out of the cups.

Tried it on the front and back halves, solid as a rock. U-joints don't show signs of rust, and they are sealed, so no grease points.

last ujoint that failed on me felt tight and wasn't until I took the drive shaft off to feel it binding in motion

The bearing that's inside the external parking brake has failed you I believe.

Talking about the drive-line drum brake?

Yes. There is a bearing in there. I have seen them fail

Well the noise has died down to mostly nothing. How crucial is it to the drive-train? I've been daily driving it, but it's going on a 400 mile adventure next month.

If it in fact is your issue it is very important. If it falls you will be walking...

I would put a floor jack on the rear diff and get it up in the air to take the load off things. Then see if drive line moves or the pinion seal is leaking or any movement there or the carrier bearing and housing. Also look for any damp spots around the brake drum housing areas. Damp spots will be seals taken out from bearings gone out.

Well heck. There is some type of fluid on the parking brake. Guess I will have to start pulling. Anyone know where I can get parts for it? Would it be the same as an F350 rear drum?

That brake is SD only. Pickups didn't have it because of parking brake at wheels.
I'm not sure if you will get parts aftermarket. I would disconnect driveshaft from it and spin and listen. I am not there to hear it in person like you are to gauge where it exactly is coming from

Take a picture of the oily spot and post it. Its worth a thousand words. It could be a number of things. Does the oil smell like brake fluid or gear lube? Even oil on a drum brake back there can cause vibration once it heats up.[then seizes up] . yehaaaaa

Just parked her, I will grab a picture tomorrow. The last bump I hit before the driveway shook the hell out of my front end, which is new. I picking up the Torx bit tomorrow to take the driveshaft off and play with stuff. It's a Torx 45, for the shaft, correct?

Eureka! Found my little rattle problem.
https://cimg6.ibsrv.net/gimg/www.for...ddfa0335f0.jpg
https://cimg0.ibsrv.net/gimg/www.for...15edd90837.jpg
That little ring is just flopping around. Guessing it had something to do with holding the pinion gasket in place, since it's starting to leak.
As for the parking brake, it's been dripping little by little since I got it. Fluid looks like DOT3 and smells likes gear oil.

https://cimg8.ibsrv.net/gimg/www.for...ca6d191c59.jpg
https://cimg9.ibsrv.net/gimg/www.for...98884e4796.jpg
https://cimg1.ibsrv.net/gimg/www.for...37f5a01011.jpg
How-to's and part numbers are welcome.