Hello Everyone, Please weigh in. This one has me worried!

Ive an 1989 740 Turbo with the M46 tranny and Overdrive Unit. The M46 went thru a few iterations (ive had them all on this 350K car) and now its just the OD unit that gives me fits.

The OD now refuses to engage even though indicator works. It was rebuilt once before by Volvo with the heavier duty pistons and o-rings. Upgrading to 30 weight also helped for a while.

Complicating my life is that the rear diff sings...loudly. Time to rebuild or replace. Rebuilding it seems cost prohibitive.

I happen to have a good low mileage M47 traditional 5 speed in my garage (1023608) including the drive shaft, etc.

The donor car is still around, and I could now go get the axle assy so that those at least match.

Things I am aware of:
1) Turbo car vs non-turbo car tranny and axle. I baby this thing as its just simple transportation. I don't lean on it.
2) Electronic Speedo sensor: I need this and I understand from Davebarton.com on "limited slip differentials" that there are a lot of combinations.
3) My existing diff and axle are 1216268 and the ratio is 3.54 per the sticker on the axle housing.

Right now I am stuck in 4th gear, and this sucks. Any thoughts, clues, or pointers GREATLY appreciated.

KY740