Recently purchased a 2000 Disco II. It has a vibration that starts at about 35mph and begins to smooth at approx 50mph. most noticeable when accelerating. Previous owner replaced rear shaft. I replaced front shaft and rear roto-coupling...still vibrates.

 

wheels might need balanced

 

I was going to say the same thing - I have the same problem (at 74MPH) and it might be my front tires or even the rotors.

I need to spend a little time checking these two things over.....

 

Get your wheels balanced.

 

What front shaft did you get?
TW shafts are known to vibrate at higher speeds.

 

x2 wheel balance and have them do a front alignment also. Cheap and will make a world of difference.
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HANDJOB JAPANESE

 

If you've been offroading in mud did you clean your wheels well afterward? Even balanced wheels will feel out of balance if they have clumps of mud caked on them. Look at the back side of the front wheels.