I have a th400 being driven by a 396. The tranny came off of a 454 originally. It has a floating (spline?), in other words the driveshaft is not bolted into the tranny, this is the way it was originally, it just slides in and the length of the (spline?) is long enough so that there is no way it will come out, it almost bottoms out. The rear end is a dana 60 with 3.54 gears. Question I have is: it whines while accelerating, even if I barely give it gas. When I let off the gas and coast it is quiet. It is not engine rpm related, it does it according to speed. It does not do it until I get to about 20 mph, so it only does it in 2nd and 3rd. I have checked the u-joints, and the tranny fluid was changed with a new filter. It is not slipping and has great torque. Does not shift up and down at will, even if I floor it it will not down-shift unless I am going slow enough. Shifts pretty strong. I turn my head sideways while driving and the ear closer to the front of the truck hears it strongest, so I know it is not the rearend diff. I have put it up on a lift and ran the drivetrain and it does not appear to be wobbly or unbalanced.
I am thinking torque converter or tranny pump.
Ideas?
H.