Steering juddering ?

Hi Guys, any thoughts on this one......when turning my 325i in a tight space today a strange rumbling noise started under the bonnet, the wheels locked up on full lock and it was a hell of a job to turn the wheel.....following some juddering I got the car out of this tight turn and it was a straight ride home....But at turning into my driveway again the juddering and loss of power steering.

I have checked the power steering fluid and its full.

Can anyone assist as to what this might be?....and how to check.....thanks in advance guys.