The 'pre-tension' you mention is also called 'pre-load', which is a standard way of adjusting wheel bearings, as well as other bearings. The whole purpose is to make sure the bearing is neither too tight, which will accelerate wear, nor too loose, which will disturb wheel alignment, also cause wear, and if loose enough, will affect braking. There are torque specifications for pre-load and final load adjustment, but I don't recall them at the moment- something around 15 ft-pounds while rotating the wheel for pre-load, then loosen the bearing and tighten it to a lower level. Some published methods use the 'flats' on the spindle nut: rotate the wheel while tightening the spindle nut 'firmly', usually using channel-lock pliers, then back off (loosen) the nut 1 or 2 flats; then move a flat to align one of the slots with the closest cotter pin hole in the spindle. Two flats is sometimes too loose, so you would tighten the nut to the closest cotter pin hole. Insert the cotter pin and you are finished. The wheel should rotate freely and there shouldn't be any detectable movement in the bearings when you are finished. In the shop, most people develop a feel for the adjustment and use the 'pliers and flats' method. In the past, there were torque wrenches made for adjusting wheel bearings, but I don't think they caught on very well.
Until you are experienced and comfortable with the 'flats' method, you probably should use the torque method and/or the vehicle manufacturer's method.
Also, make sure you install the seal so the sharper edge of the sealing surface faces the inside of hub, or you will end up with grease on your brake linings. Typically, the 'outside' of the seal is smooth and has the manufacturer's part number stamped on it; the 'inside' typically has all the crimps on it to hold it together. Also, most seals have a light-weight coil spring around the inner circumferance of seal suface; the spring helps keep the seal in contact with the intended surface.
Harvester
