Lull 944E-42 Service Manual - Manual (Page 764)

Stabil-TRAK™ System
10.6 Model 644E-42/944E-42 Rev. 6/04
10.3 STABIL-TRAK™ OPERATION
The rough terrain forklift rarely operates on ground that is
a smooth, flat surface. As its name infers, the
“Construction Rough Terrain Forklift” is typically found on
worksites with numerous holes, trenches, rocks and
slopes.
To negotiate this type of terrain, rough terrain forklifts are
designed with a free oscillating rear axle. This design
enables the operator to drive over changes in terrain with
minimal concern for what the rear tires are going over.
With oscillation, the rear axle will rotate upward or
downward when a tire meets with anything causing it to
raise or lower. The rear of the vehicle moves up or down
approximately one-half the distance of the tires
movement, while giving the vehicle minimal lateral
movement. The oscillation capability is necessary for
traveling across rough terrain.
The rear axle is capable of oscillation; the front axle is
normally locked to the vehicle frame by the frame sway
cylinder. The frame sway cylinder does allow for
adjustment of the frame and load to a level position when
traveling on a rough terrain worksite, or for leveling a
load.
The least stable condition for the rough terrain forklift is
when the boom is raised and the carriage is empty. This
is because the center of gravity is now high and closest
to the rear apex of the stability triangle.
10.3.1 Understanding the Stabil-TRAK™
System
The following information explains the difference between
a typical telescopic handler and the benefits that the
Stabil-TRAK™ system provides.
Most telescopic handlers operate within a 3-point stability
triangle (1) as defined by points A, B and C.
Point 2 in the illustration represents the center of gravity
of an unloaded vehicle. The load has its own center of
gravity represented by point 3. When the vehicle is
loaded, the vehicle and load become one mass with a
combined center of gravity, represented by point 4.
As the boom is lowered or extended, point 4 will move
forward in the 3-point stability triangle, or backward in the
3-point stability triangle as the boom is raised. Point 4 can
also move left or right toward the edges of the stability
triangle if the frame is tilted. As long as point 4 remains in
the boundaries of the 3-point stability triangle (1), the
vehicle will remain stable. If point 4 ever goes beyond the
boundaries of the stability triangle, the vehicle can tip
over.
In the LOCKED MODE, the exclusive Stabil-TRAK™
System provides a 4-point stability rectangle (5) by
positively locking the frame to the rear axle through the
stabilizer cylinder. The vehicle is then supported at four
points; A, B, D and E. While in the LOCKED MODE, it is
clear that point 4 will remain within the entire boundary of
the 4-point stability rectangle, giving the operator more
flexibility in positioning the load.
MT2780
A
B
C
D
E
1
2
3
4
5