Steering viberation

Hello
I have a 1988 rr 3.5. I get this vibration through the steering wheel at 50mph when the transmission is loose. If I put the autobox into 3rd it goes. The car has polybushes, A fairly recent recon s/box, I have changed the steering damper. Has anyone any ideas please.
Mik

Hi the vibration could be because the wheels are out of balance or you have a stuffed ball joint, bent stearing arm, incorrect play in the steering, buckled wheel, loose wheel, and one of the worst incorrectly fitted or totally the wrong wheels (yes the wrong wheels all wheels will not go on any vehicle even if they appear to be the same size)

or it could be the viscous coupling (I had a certain 4x4 centre in Norwich convince me it was viscous coupling when it was a ball joint neadless to say I don't hold them in good asteem)

Charlotte

Hi Thanks for the reply. All the wheels and tyres are ok and balanced. Steering box newish, steering link new. So I think it could be the swivle pin preload. So I am going to recon the whole lot.
Regards
Mik

Check the propshaft's U-joints, and splines. Holding one end of the propshaft and twisting or shaking the other, there should be no discernible play. It's easier to check with the propshafts off, but can be done with them on.