Originally Posted by SlowerOne

It should be impossible to turn - totally tight. Any slip you can exert with your hand needs to be eliminated. A good diff build will be smooth as glass and tight as a drum. It isn't usually the diff that causes the car to take of at an angle, it's usually an uneven width of the rear axle from side to side (not centred) or the same problem when comparing front and rear track - the rear track is offset compared to the front.

After that there are scores of small things it could be, so best find one of us at a meeting and we'll sort it out. HTH