3.91 diff

[ecorrea21]

I was given a diff from a buddy who bought it to replace his blown diff. While his car was parked in front of his house it was hit and totaled.

The tag reads 3.91 596 what does it fit?

I know the limited slip units have an S preceding the # but when I spin the input shaft, the outputs both rotate the same way. I thought in an open diff the outputs rotated in opposing directions?

[SchnellerVert]

596 relates to a replacement date if I remember correctly.