Help diagnose squeak/squeal?

[robm630]

So... my c10 with a th700-r4 has developed a low speed squeak/ intermittent squeal. It only happens below 60kph. In drive, not reverse. And I thought it might be the driveshaft, so over the last week I rebuilt the entire driveshaft, 3x new u-joints and new center/carrier bearing. And buffed it up and painted it, and it's super nice now, and that had solved a vibration I knew was from a bad ujoint. But the squeal/squeak has persisted.

When I was installing the front half of the driveshaft I turned the tranny while it was in neutral and it did squeak even just at slow speed... is this just going to be the seals on the output that the shaft slides into? Or do I have something bad happening in there..

Edit: forgot to mention. If I'm on, or ride the brakes. The squeak completely disappears... it's not any of the wheels/brakes either. When I had it on Jack's I spun everything.. it's emanating from the back of the transmission.
from

 

[Robert Bare]

Did you grease the output seal before installing shaft??

 

[robm630]

Did you grease the output seal before installing shaft??

Yessir. Real good. And it kind of altered the squeal. For a bit. But it just went back to it within 10km

 

[Robert Bare]

Well, could be a trans problem. But, you could try some Teflon grease on the output splines, grease up the inside of the yoke.

 

[robm630]

Well, could be a trans problem. But, you could try some Teflon grease on the output splines, grease up the inside of the yoke.

I'll give this a shot later this week.

 

[NickTransmissions]

I'll give this a shot later this week.

Get the truck up on all four jack stands (or a lift), put the key on, engine off thn shift the trans into neutral. Then go under the vehicle and spin the drive shaft clockwise as it would spin when in Drive - if you hear squealing sound coming from the transmission, record it the post it to Youtube - share the public link here...

If it's what i think it is, it's totally normal.