My 1977 123 series 240-D vibrates a little between 55 - 65 km/hr speeds in 4th gear manual shift ( at around 40 in 3rd gear). This vibration is so brief that is often not noticed/felt by the passenger but nags me. I replaced all 4 tyres, both the drive-shafts, flexdiscs, u-joint and the center bracket and its bearing over a period of 6-months but there is no change in the vibration pattern or the speed at which the car starts to vibrates.

Any suggestion on how to get rid of this annoying vibration.

Obaid