I just got an 87 245dl with a bunk 5 speed, it makes some great noises in all gears but 4th. The question is can i replace it with an m46 4 sp. w/ od???? I know i'd need m46 driveshaft and tranny mount. is their a difference in the tranny input shaft length? or any thing else. thanks

I weighed the facts on mine and installed another M47. It came out of a 95, I think, 740. Changed the mount and installed it. I just do not like the clunk the M46 gives going into OD..Plus they are different ratios.
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Max..1989 244 DL 5 Spd., V15 Phase II Cam Bilstein HD, Turbo Swaybars, Poly Bushings all round, Turbo Wheels, Black leather interior, Electric mirrors, LED dash and gauge lights and now NEW ECODES with the turn signals, 1992 black 244 next project

I did this conversion a few years ago. It is a straight swap, but you need the drive (prop) shaft from the donor car. The front half is a different length, and the back, although the same length, may have a different diameter so not connect up.
If you are going with the standard electrics- button on the gearlever knob, etc, you need all the wiring and the relay. Note - you must get the manual relay, not one from an automatic.

Overdrives do not clunk if they are working properly. Mine has now done over 400,000 miles without a service, and it changes almost imperceptibly. That's without declutching, but feathering the accelerator a little to matvh the speeds.

It's well worth the conversion in my view. It's a joy just to flick the switch for 5th gear, instead of doing a silly cross-gate change every time with the M47.

I know the feeling. I bought an M47 like the one you describe from the JY by mistake. Same problem. Only functioned in 4th gear. The teeth on the input shaft were all torn away. 4th gear is 1 to 1 so it directly connects the input and output shafts without going through any of the toothed gears.
Unless this is a turbo car, I would look for another M47. They have a bad reputation due to lack of lubrication but its hard to break one unless you do something really stupid like hit reverse while going forward (thats how you are only left with 4th). For the M46 you will need the front half of the drive shaft, and maybe the cross member. Not sure about that last one. The M47 is smaller and lighter than M46.
Good luck

Sounds like you have the typical m47 bearing failure. The m46 and m47 are interchangable. The m47 cars have the dished flywheel/clutch and the NA M46 cars have the flat flywheel, but the m46 will work on either.

You will also need the wiring harness, and relay to operate the overdrive, and the m46 shifter. You may need aluminum spacers that go under the crossmember. From what I have seen, the m47 crossmembers don't have them, and most m46 gearboxes do have them. When I did the conversion on my 89 I didn't use the spacers and the gearbox sat up too high. I had to go back to the junkyard to find the spacers.

The crossmembers are sort of interchangable. I converted my 93 from and auto to m46. I actually used the Auto crossmember and mount. They are not the correct parts but I they are working fine.

If you are putting on a used M46 I would suggest rebuilding the OD before you install it. It's much easier to do when the gearbox is on a bench, and it will work much better.