General Shuddering over 50mph

[euroben]

I needed a new propshaft because of the central bearing fell apart. I bought one off eBay and it looked well made and and I measured it and it was the same length as the original (very important). I fitted the new propshaft myself and all seemed perfect until I hit the motorway and the second I went over 60mph it vibrated so badly I thought the car was going to fall apart. Drop below 60mph and it was smooth again. So when I got back I removed the propshaft again and decided to get my garage to fit it for me because the eBay seller said they would only accept returns if it had been fitted by a garage. My garage fitted it for me and to my surprise it is now perfect with no vibration at any speed. Same propshaft! Looking at it, they have fitted it exactly as I did. I think although it seems easy to replace, I think it might be possible to seat it slightly off balance somehow. Possibly you need to be very precise on the torque setting. It may be worth while getting another garage to fit the prop for you and see if it makes a difference.