I did not switch crown and pinions as pairs. If this is the case, then i guess i'm fucked.
It's a 5.speed.

Isn't the differential and gearbox separate? I did not refill the gearbox, but the noises are clearly from the diff.
The sound gets higher as i pick up speed, and it's the same in all gears. I'm 100% sure it's not the gearbox.

I used SAE 80W/90 Mineral in the axle. I filled it up to the "inspection ...

So, welded up a differential i had laying around for my car, mounted it and tested it. As soon as i put second gear i started hearing some whining noise.
This noise got worse as i got more speed. I Assume it's some trouble with the shims ?
I drove the car like this for about a month, and yesterday ...