I have a 1990 760 that I have owned for 9 years. The drive shaft knocks when accelerating from a standstill, under load (uphill) at around 1800 rpm. Coming up my inclined driveway. It does it everytime, at the same speed, and has for several years. The knock feels and sounds like it it under the center console. It never does anything odd at speed. It is a minor annoyance but I have decided to see if I can fix it.

The u-joints and centerline bearing and housing as sound.

Any ideas would be appreciated.

Maybe the tranny mount is bad and its hitting the frame?

Besides the condition of the u-joints, center support rubber, and center support bearing, check the tranny output shaft bushing for play.

What about looking into the old TSB on shimming the center bearing housing. Worked for the 780 years ago.

does anyone have this technical SB???

Hawk

"Driveline Take-Off Vibration: Shimming May Be Required. From Volvo Technical Service bulletin 45/102 Jan '91. [Symptom:] Take-off vibrations at low speed, especially with high acceleration and/or heavy load, can occur in some cases. [Solution:] The level of vibration can be reduced by changing the vertical position of the center support bearing. Best results differ from car to car. Start with a change of 6mm (1/4") upwards. If results are not acceptable, try positions from 5mm (3/16") downwards to 12mm (1/2") upwards from the original position. Note that clearance between drive shaft and fuel lines must be at least 20mm, and between drive shaft and the fuel tank at least 16mm. Shimming upwards should not exceed 12mm (1/2") and after re-positioning the center support bearing housing should not contact the floor pan."