1990 BMW 8 SERIES technical data

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Page 1 of 25

BMW 8 SERIES 1990 E31 Cruise Control Acutator BMW Cruise Control Actuator
1985 to 1996
Technical Data
November 26, 2005

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BMW 8 SERIES 1990 E31 Cruise Control Acutator Table of Contents
Usage Cross Reference ................................................................ 3
Theory of Oper

Table of Contents
Usage Cross Reference ................................................................ 3
Theory of Operation .................................................................... 5
Actuator Failure Modes ................................................................. 6
External Description .................................................................... 7
Internal Description ..................................................................... 9
Throttle Cable Removal .............................................................. 10
Disassembly ............................................................................. 13
Actuator Removal ...................................................................... 21
Circuit Board Pictorial ................................................................. 24
Circuit Board Schematic ............................................................. 25
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BMW Cruise Control Actuator 1985 to 1996 – Technical Data page 2 of 25
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BMW 8 SERIES 1990 E31 Cruise Control Acutator Usage Cross Reference
This actuator was used on several BMW models from October 1985
through May 1999. The chart below may be used to cross reference
the usage of the actuator.
Part #: 6571137831

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BMW 8 SERIES 1990 E31 Cruise Control Acutator Usage Cross Reference
E34 520i Touring M50 Europe Nov-90 Jun-96
E34 525i Touring M50 Europe Dec-90 Jun-96
E34 525ix Sedan M50 Europe Apr-91 Dec-95
E34 525ix Touring M50 Europe Jul-91 Mar-96
E34 M5

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BMW 8 SERIES 1990 E31 Cruise Control Acutator Theory of Operation
The throttle is simultaneously linked by cable to the cruise control
actuator and by a second cable to the accelerator pedal. The core of
the cruise control actuator is a smal

Theory of Operation
The throttle is simultaneously linked by cable to the cruise control
actuator and by a second cable to the accelerator pedal. The core of
the cruise control actuator is a small motorized drum which winds or
unwinds a belt of rubberized fabric. This control belt is affixed to the
cable connected to the throttle. Thus, by winding the belt the throttle
cable can be retracted, or by unwinding it can be extended.
When the cruise control is not in use, the motor drive is disengaged
from the drum. This allows the drum to turn easily and the throttle
cable to move freely in response to accelerator pedal action. A
clockwork style spring supplies mild tension to keep the belt wrapped
around the drum and also takes up slack from the throttle cable.
A solenoid is used to engage the motor drive with the drum. When the
solenoid is energized a small armature is moved which pushes a
sprocket into contact with the integrated gear on the drum. At this
point, if current is supplied to the drive motor, the drum will wind. If
the polarity of the current is reversed, the drum will unwind.
The control unit (“brain”) is located in the electronics bay. The control
unit can thus command the actuator to engage or disengage, to reel in
the throttle cable or extend it. This provides the necessary control
capabilities.
To maintain a set vehicle speed, the control unit needs to know the
rotational position of the drum. A potentiometer (variable resistor)
integrated into the drum supplies this information to the control unit.
A resistance proportional to the position of the drum is constantly
presented to the control unit. This feedback allows the control unit to
determine how the actuator has responded to its commands.
By using the current vehicle speed (supplied by another sensor) along
with the feedback from the actuator, the control unit can adjust the
actuator as necessary to maintain vehicle speed.
BMW Cruise Control Actuator 1985 to 1996 – Technical Data page 5 of 25
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Page 6 of 25

BMW 8 SERIES 1990 E31 Cruise Control Acutator Actuator Failure Modes
The cruise control actuator will seem to work only intermittently or
partially when a tooth is broken in the gear driving the control belt
drum. This is because the control

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BMW 8 SERIES 1990 E31 Cruise Control Acutator External Description
The cruise control actuator is enclosed in a two part plastic housing.
The throttle control cable protrudes through a fixture on the top half.
A round male electrical connecto

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BMW 8 SERIES 1990 E31 Cruise Control Acutator External Description
Figure 4 - Actuator side view
Figure 5 - Actuator bottom view (mounting plate and cable removed)
BMW Cruise Control Actuator 1985 to 1996 – Technical Data page 8 of 25
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