Dave - the Xantia's lower engine mounting is the same design as the one that gave up on my Xm. There's a lower big rubber donut [about 80mm approx] that stops the engine rocking when torque through the gearbox is driving out to the driveshafts when the clutch is engaged.
I determined just how shot to hell the rubber bush was on my Xm by getting the car up on a strong pair of ramps whilst a HIGHLY trusted friend engaged 1st and lifted the clutch up whilst he stood on the brake pedal with the handbrake on...
As I said, he's highly trusted!! Anyhow the engine moved a good 3/4 of an inch due to a well stuffed mounting.
Every time the clutch is engaging drive the engine is trying to do a somersault but is held in check by the gearbox hanging mounting, the top mount which has a kind of bump stop rebound AND the lower casting that's attached to the engine crankcase; this houses the donut engine stabiliser as well as a cutout that houses an intermediate bearing race on the long offside driveshaft.
It cost me 140 quid new from Citroen.
I'd wager this will be at least a contributory problem to your judder on taking up drive unless you've got a duff thrust bearing/clutch pressure plate. A clutch judder would be there all the time whereas the engine mount problem will only be there when there's a heavy load where you engage the drive on engaging the clutch.
Andrew
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