oil level BMW 525I TOURING 1989 E34 Level Control System Manual

4
Level Control Systems
Hydropneumatic Rear Leveling System
This module pertains to the hydropneumatic rear suspension system with the engine dri-
ven piston pump. The earlier system using the electro-hydraulic pump will not be dis-
cussed.
The self-leveling suspension system is designed to maintain vehicle ride height under
loaded conditions.
The system is fully hydraulic, utilizing a tandem oil pump to supply pressure to both the
suspension system and power steering system.
The system is installed on:
 E32 - 735 iL, 740iL and 750iL
 E34 - Touring 525i and 530i
 E38 - 740 iL and 750iL

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

6
Level Control Systems
Tandem Pump
The tandem pump consists of a vane pump for power steering and a radial pump for self-
leveling suspension. Both pumps are driven by the same shaft and have separate oil feeds
for each system.
The radial pump has the capacity to pump 102 liters of oil per minute. The maximum pres-
sure is limited to 1900 Psi (130bar) by the pressure regulator located on the control valve.

7
Level Control Systems
Oil Reservoir
The single reservoir stores fluid for both the self-leveling and power steering systems.
Incorporated in the reservoir, is a reed type level warning switch. If the fluid level drops and
the contact closes, a signal is sent to the check control module and a warning will be dis-
played in the instrument cluster matrix display.
The hydraulic fluid required for the self-leveling suspension system varies between models
and installed equipment. The following fluid is used:
 Pentosin CHF 7.1
 Pentosin CHF 11S
 Power Steering Fluid (BMW)
This type of fluid is used because of its
low viscosity and low noise characteris-
tics. It cannot be mixed with other fluid
types.
The self-leveling system fluid type is
always marked on the top of the hydraulic
reservoir. Always use the correct fluid
never mix with another fluid.
When filling the system, be aware of the
status of the level control system. If the
vehicle is loaded, the level will appear to
be low. Do not fill the system unless it is
in the resting state. Otherwise, an over-
flow situation could result.

8
Level Control Systems
Pressure Reservoirs
The oil pressure reservoirs (2) on each strut incorporate a membrane and are nitrogen gas
filled. They are designed to absorb the oil which is expelled from the struts during down-
ward movement, the gas in the reservoirs is compressed and pushes the oil back into the
struts during upward movement.
Gas Chamber
Membrane
Oil Chamber

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.