I just finished building a M46 from a 260 into a P120/Amazon. I used the bellhousing from a B23 so it would fit onto my B18 engine. Because of this, the gearbox is on a slight angle, but this is no problem: the gears still ‘splatter’ around in the oil and the OD pump also gets enough oil pressure and works fine.

When I first took the car for a drive the drive shaft vibrated a lot. I got it balanced by a profesional company: no difference. I then got it checked again and replaced the flange on the gearbox/OD (beacause revious owner had cut out litlle bits when cutting the bolts (instead of just screwing them lose)) and replaced the shaft bearing in the middle and the rubber supporting it. The driveshaft still vibrated.

I then put the car on jacks, dismanteld the differential, only leaving the pinion shaft in place, and got the drive shaft dynamically balanced again (as a whole including the bearing). Now, when I let the car run (on the jacks that is) the following occurs:
-When I don’t use a drive shaft at all, and just let the gearbox spin, there is no noticable vibartion at all.
-When I only fit on the first part of the drive shaft, and only let this first part + bearing spin around, a little vibration occours at 65 mph when I do use the OD, and at 70 mph in 4th gear.
-When I fit on the complete shaft, there is a vibration starting at around 40 mph and then decraesing, enough to let the support bearing and also the differential bearing turn quite hot (too hot to handle).

It seems to me that every time I make the drive line longer the vibration gets stronger. Since the drive shaft it self is now balanced twice I gues that part should be right. The problem is not the support bearing and not the diff. But (#^!%*^#*) what is?
Since I don’t know the history of the gearbox, could it be that the output shaft is bent just a billion of an inch or so, or a bearing in the OD is worn or, or…. Are there any vibration problems know of these M46’s? It has a vibration dampner attached to it.
By the way, the vibration still occurs when I lift the car on one side, in a way that the gearbox in then horizontal again, so that’s not causing it.

The problem discibed above is only just a summary, so please help me out here.

Ben Flierman, the Netherlands