Which cuff it torn? The one near the differential or the one near the wheel?
For the one near the differential, which sort of cuff have you got? There are two sorts:-
1. All one piece, you have to dismantle the hub and preferably the axle arm in order to get the drive shaft through the cuff. then re-assemble the axle arm back on to the differential side plate. then struggle to get the rubber cuff on both sides of the gap.
The second sort is a split cuff - like the one above but with a cut in it allowing you to place in the gap without having to dismantle anything. put it with the split pointing to the front of the vehicle and underneath the axle arm. Use some non-hardening gasket sealant on all the surfaces when you put it on.
Only the early Haflingers had a rubber cuff on the universal joint near the wheel. To fit this you have to dismantle the hub (remove the swivel pins, disconnect the brake pipe). Then pull teh hub from the axle arm. Now you have access to the rubber cuff.
Heat the rubber cuffs in hot water for 5 minutes before you fit them to make them soft and stretchy!
John