The 2nd Generation Sets
1981 NL Technical catalog
A completely new series of 5 models and 1 accessory set were released, including a large new tractor, the 8859 Harvester,
and truck, the 8848 Power Truck. It is interesting to note that after only 4 years Lego had already replaced the original tractor, helicopter and auto chassis with new, 2nd generation models. This very narrow scope of subjects, primarily cars, trucks, motorcycles, and construction/farm machinery, would continue until the late 1990's.
New elements for 1981 include the first of the 'toothed' plates, bushings and toggle joints, as well as the steering arm. These new elements allowed for a new method of construction and further refined the scale of technical functions.
1981 US ad
 
8848 Power Truck:
One of the first of the 2nd generation models, the 8848 Power Truck featured rack and pinion steering using toothed plates and the new steering arm, a rear axle differential, the front scoop and rear bed that could be raised and lowered via levers in the cockpit. The model made significant use of the new toothed elements, which allowed the technical functions to be scaled down in terms of size and resulted in a very realistic model.
 
UK patent 2,087,743
 
The toggle joint:
Connecting elements, such as a cross axle, at angles other than 90 or 180 degrees was always possible but this method of construction was fully realized with the introduction of the toggle joint. The 1981 UK patent application shows a toggle connector similar to the earlier piston rod but with a toothed rim. A pair of toggle joints could be assembled in various positions between 90 and 180 degrees by meshing of the toothed rims and could be locked in place by a connector peg or 1/2 bushing. These and other elements, such as the plate with toothing, allowed for rather compact angular connections and were widely used for years in Technic constructions.
UK patent 2,087,743
 

1981 sets:

8710 Expert Builder Parts Pack
8844 Helicopter
8845 Dune Buggy
8846 Tow Truck
8848 Power Truck
8859 Harvester
 
By Isodomus