low oil pressure BMW 740IL 1998 E38 Level Control System Manual

5
Level Control Systems
System Components
The system consists of the following components:
 Tandem Hydraulic Pump
 Oil Reservoir
 Pressure Reservoir (2)
 Control Valve with Regulating Linkage
 Camber Warning Switch (E32 and E34)
 Rear Shock with LAD Module
 Expansion Hose, Pressure Lines and Distribution block.
Component Layout E32

9
Level Control Systems
Control Valve
The rotary control valve located on the rear suspension has three positions:
 Raise
 Level
 Lower
The control lever is attached to the rear stabilizer bar to sense vehicle loading. When the
vehicle is loaded (passenger or luggage) the suspension drops and the stabilizer bar twists.
The control lever is moved in the "raise" direction.
With the engine running, oil flows from the pump to the bottom of the rear struts. The body
of the car is lifted and the control lever returns to the level position.
In the level position, the oil
bypasses the valve and
returns to the reservoir
through the return line.
A minimum pressure of
440 Psi (30bar) is main-
tained at all times. If ser-
vice is required, a bleed off
valve is installed on the
control valve to drain the
systems pressure.

11
Level Control Systems
LAD Module
With a high pressure applied to the control piston,
the flow resistance is high and the damping force
will be stiff.
The load dependent module is a control valve
that regulates the flow of oil between the strut
and the pressure reservoir.
The control piston in the (LAD) moves in rela-
tion to the pressure applied from the pump.
This movement will regulate the tension on the
inner spring of the module. With only a low
pressure applied, a small amount of tension
will be applied to the spring. Little flow resis-
tance will be developed between the strut and
pressure reservoir. The damping force is soft.