1999 BMW 525i steering

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300-8
Suspension, Steering and Brakes - General
Rear suspension Sport Wagon
(EHC with air springs)
Air sprIn9 Shock absorber I
(tiaction strut) arA
(lower control arm) Integral arm 502330210
EHC initiates a control sequence as necessary. The system
offers the following features:
Control system independent from vehicle engine (no en-
gine driven hydraulic pump system)
Individual control of rear wheels
Uneven load identified and compensated for
Uneven road surfaces identified and not compensated for
Automatic control interrupted when cornering
System diagnosable using the
BMW Service Tester (DIS-
plus, GTI, or MoDiC)

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300-1 0
/Suspension, Steering and Brakes - General
The steering system features variable power assist provided
by an engine-driven hydraulic pump.
Rack and pinion steering
6-cylinder models
(525i, 5281, 5300
Two types of steering systems are used in E39 models. 6-
cylinder (525i, 5281, 530i) models are equipped with a steer-
ing rack system. V-8
(540i) models are equipped with a re-
circulating ball and nut steering gearbox.
Rack-and-pinion steering
Steering components in 6-cylinder models consist of a rack-
and-pinion type steering gear and connecting linltage to the
road wheels.
The steering linkage connects the rack-and-pinion unit
through tie rods to the steering knucltles. The tie rod ends al-
low the wheels to pivot and react to suspension travel.
Recirculating ball and nut steering
V-8 models
(540i)
I
Recirculating ball and nut steering
Recirculating ball and nut steering in V-8 models consists of a
steering box with integrated hydraulic control valve and con-
necting linkage to the road wheels.
Thesteering linkageconnects the steering gearbox through a
pitman arm to the wheels. An idler arm maintains correct toe
angle. The tie rod allow the wheels to pivot and react to sus-
pension travel.
E39 cars are equipped with power disc brakes with integral
antilock brakes (ABS). The parking bralte is a dual-drum sys-
tem integrated with the rear brake rotors.
Power assist is provided by a vacuum booster when the en-
gine is running. The brake pedal
pushrod is connected direct-
ly to the master cylinder, so failure of the vacuum booster
does not normally result in total
bralte failure.
Each disc bralte uses a caliper with a single hydraulic cylin-
der. Brake pads in the left front and right rear contain wear
sensors. When brake pads need replacement, the sensors il-
luminate a light on the dashboard.

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Suspension, Steering and Brakes - General
WHEELS AND TIRES
Tire size is critical to the properoperation of the antilock brake
system and traction control system. Several differentstyles of
wheels in
15,16, and 17 inch diameters are available from an
authorized BMW dealer.
Rim and tire size applications are listed in the table below.
Rim and tire sizes table
ELECTRONIC BRAKE AND STABILITY
CONTROL SYSTEMS
Model
5251
5281
530i
540i (manual
transmission)
540i (automatic
transmission)
All
E39 vehicles are equipped with the Antilock Braking Sys-
tem
(ABS). Early production models featured ABS with Auto-
matic Stability
control (ABSIASC). Later models came
equipped with ABS and Dynamic Stability Control
(ABSIDSC). DSC builds upon the existing ABSIASC system
to provide electronic control of drive and braking systems to
insure vehicle stability.
This manual will refer to these systems as ABS. ASC or DSC
will be specified when necessary. ABS component replace-
ment is covered in
340 Brakes.
Standard
ABS applications are shown in the accompanying table
Rim size
16x7
15x7
16x7
17x8
16x7 Optional
Tire size
225160R-15
235145-1 7
225155-1 6
Rim size
17x8
Front 17
x 8 Rear 17 x 9
17 x 8
Front 17x8
Rear 17x9
Front 17 x 8
Rear 17 x 9 Tire
size
245145R-17
Front 235145-1 7
255140R-17
235145R-17
Front 235145-1 7
Rear
255140R-17
Front 235145-17
Rear 255140R-17

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300-1 2
I Sus~ension, Steerincl and Brakes - General
E39 electronic brake and stability control
systems application table
(528i, 54bi) Traction (ASC) I Hydraulic unit in right rear of engine compartment 1
Identifiers
Year (model)
I No precharge pump 1
Manuf. up to 911998 l~utomatic Stability Control plus I Electronic control module next to glove compartment
System
Precharge pump in
lefl front of engine compartment, below
steering fluid reservoir
Separate rotational rate (yaw) and lateral acceleration sensors
I I
Combined rotational rate (yaw) and lateral acceleration sensors
Electronic control
module next to glove compartment
Hydraulic unit in right rear of engine compartment
Manuf. up to 911999
(540i optional)
I I
ABS system
Dynamic Stability Control (Bosch
DSC
Ill v. 5.3)
The electronically controlled
ABS maintains vehicle stability
and control during emergency braking by preventing wheel
lock-up.
ABS provides optimum deceleration and stability dur-
ing adverse conditions. It automatically adjusts brake system
hydraulic pressure at each wheel to prevent wheel lock-up.
Control
moduleihydraulic unit
in right rear of engine compartment
No precharge pump
Manuf. from
911999
(all models)
Automatic Stability Control (ASC)
Dynamic Stability Control (Boscli
DSC Ill v. 5.7)
NOJE-
ASC (Automatic Stability Control) may also be referred to as
ASCiT (Automatic Stability ControkTraction).
ASC works in conjunction with ABS and the engine manage-
ment system to enhance vehicle control. The main function of
the
ASC system is to maintain the contact between the tires
and the road surface under all driving conditions. This is
achieved through exact application and management of brak-
ing and drivetrain forces.
The
ASC system improves traction by electronically applying
the rear brakes when the rear drive wheels are spinning at a
faster rate than the front wheels. The combined
ABSIASC
control module, operating through the ABS hydraulic control
unit, modulates braking force at the rear wheels.
In addition,
ASC overrides the throttle opening to reduce en-
gine torque and maintain vehicle traction. Because the throt-
tle is controlled electronically, the driver cannot increase
engine power output during
ASC intervention regardless of
how far the accelerator pedal is pushed.

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Suspension, Steering and Brakes - ~enerail
The main components of the system are the wheel speed
(pulse) sensors, the
ABSIASC or ABSIDSC control module,
and the hydraulic control unit.
Traction control also comes into operation during decelera-
tion. Decelerating on snowy or icy road surfaces can lead to
rear wheel slip. If a rear wheel starts to drag or lock up, the
ASC system can limit the problem by adjusting throttle, fuel
injection and ignition timing.
4 A switch (arrow) on the center console is used to toggle the
ASC on or off.
NOJE-
Even with the ASC system turned off, if the ASC control mod-
ule senses a difference in wheel speed (one wheel spinning)
the
ASC system applies modulated braling force to the slip-
ping wheel until traction is regained. There is no override of
fuelinjection function.
The ASC system is designed to be maintenance free. There
are no adjustments that can be made. Repair and trouble-
shooting of the ASC system requires special test equipment
and knowledge and should be performed only by an autho-
rized
BMW dealer.
ABSIASC traction
I 1.
control system
Wheel speed sensor
Wheel speed pulse wheel
Brake disk
Brake caliper
ABSIASC hydraulic unit
Brake master cylinder
Pedal operated throttle valve
ASC controlled throttle valve
Engine control module (ECM)
Accelerator pedal
ABSlASC control module

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Suspension, Steering and Brakes - General
Front ride height specifications
(measurement
A)
E39 6-cylinder (5251,5281,530i) models
E39
V8 (540i) models
Wheel size
15 inch
16 inch
17 inch
18 inch
Maximum variation between sides: 10 mm (0.4 in)
Maximum deviation from specifications: 10 mm (0.4 in)
Standard
suspension
579 mm (22.8 in)
592 mm (23.3 in)
607 mm (23.9 in)
620 mm (24.4 in)
Wheel size
15 inch
16 inch
17 inch
18 inch Sports suspension
559
mm (22.0 in)
572 mm (22.5 in)
587 mm (23.1 in)
600 mm (23.6 in)
Maximum variation between sides: 10 mm (0.4 in)
Maximum deviation from specifications: 10 mm (0.4 in)
Standard
suspension
579 mm (22.8 in)
592
mm (23.3 in)
607 mm (23.9 in)
620 mm (24.4 in) Rough
road suspension
599
mm (23.6 in)
612 mm (24.1 in)
627 mm (24.7 in)
640 mm (25.2 in)
Sports suspension
559 mm (22.0 in)
572 mm (22.5 in)
587 mm (23.1 in)
600
mm (23.6 in)
M sports package
559 mm (22.0 in)
572 mm (22.5 in)
587 mm (23.1 in)
600 mm (23.6 in)
Rough road suspension 599 mm (23.6 in)
612
mm (24.1 in)
627
mm (24.7 in)
640
mm (25.2 in)
M sports package
562 mm (22.1 in)
575 mm (22.6 in)
590
mm (23.2 in)
603
mm (23.7 in)

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300-1 6
I Suspension, Steering and Brakes - General
Rear
ride height specifications
(measurement
A)
E39 6-cylinder (5251,5281,530i) models
E39 VB (540i) models
Wheel size
15 inch
16 inch
17 inch
18 inch
Maximum variation between sides: 10
mm (.04 in)
Maximum deviation from specifications: 10
mm (.04 in)
Standard
suspension
547 mm (21.5 in)
560
mm (22.0 in)
575 mm (22.6 in)
588 mm (23.1 in)
I I I I I
Maximum variation between sides: 10 mm (.04 in)
Wheel
size
15 inch
16 inch
575 mm (22.6 in)
Maximum deviation from specifications: 10 mm
(.04 in)
Sports suspension
532 mm (20.9 in)
545 mm (21.5 in)
560 mm (22.0 in)
573
mm (22.6 in)
Rough road
suspension
567
mm (22.3 in)
580 mm
( in)
E39 Sport Wagon models
M sports package
536
mm (21.1 in)
549 mm (21.6 in)
Standard
suspension
547 mm (21.5 in)
560 mm (22.0 in)
588 mm (23.1
in)l 573 mm (22.6 in)/ 603 mm (23.7 in)l 608 mm (23.9 in)l 577 mm (22.7 in)
560
mm (22.0
in) Ride level
control
562
mm (22.1 in)
575 mm (22.6 in)
590 mm (23.2 in)
603 mm (23.7 in)
Sports suspension 532
mm (20.9 in)
545 mm (21.5 in)
590
mm (23.2 in) Rough
road
suspension
567
mm (22.3 in)
580 mm (22.8 in)
595 mm (23.4 in)
608 mm (23.9 in)
Ride level control
562
mm (22.1 in)
575 mm (22.6 in)
Wheel size
15 inch
M sports package
532
mm (20.9 in)
545
mm (21.5 in)
560 mm (22.0 in)
573 mm (22.6 in)
595
mm (23.4 in)
Sports suspension with
air spring
548 mm (21.5 in)
Standard
suspension
548
mm (21.5 in)
16 inch
17 inch
18 inch 564
mm (22.2
in)
Maximum variation between sides: 10 mm
(.04 in)
Maximum deviation from specifications: 10 mm
(.04 in) 561
mm (22.0 in)
576
mm (22.6 in)
589
mrn (23.1 in)
561
mm (22.0 in)
576 mm (22.6 in)
589 mm (23.1 in) Ride level
control
563
mm (22.1 in) Rough road suspension
568 mm (22.4 in)
576 mm (21.6 in)
591 mm (23.2 in)
604 mm (23.7 in) 581
mm (22.9
in)
596
mm (23.5 in)
609 mm (24.0 in)

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31 0-2
I Front Suspension
This repair group covers the repair and replacement of com-
ponents that make up the front suspension of E39 cars.
Two different types of steering systems are used in the E39
series. 6-cylinder
(5251,5281 and 530i) models are equipped
with a rack and pinion type steering system mounted to an
aluminum subframe.
V-8 (540i) models use a steering gear-
box type system mounted to a steel subframe.
See
300 Suspension, Steering and Brakes-General for a
description of the front suspension and components, as well
as specifications for setting ride height.
CAUTION-
Some E39 models are equipped with aluminum suspen-
sion components. The foiiowing cautions apply:
Due to the chemical and corrosion characteristics of
aluminum, do not bring into contact with battery acid.
* Do not clean with wire brushes with brass or iron bris-
ties. Only use brushes with stainless steei bristles.
Do not expose to flying sparks from grinding/cutting op-
erations.
* Do not subject to steei welding splashes.
Do not expose to temperatures over 80°C (176°F).
even for short periods. Temperatures in painting faciii-
ties are not a problem.
Special tools
Special service tools are required for most of the work de-
scribed in this repair group. In addition to the tools depicted in
the illustrations, avariety of press tools are necessaryfor con-
trol arm bushing replacement. Read the procedures through
before beginning any job.
31 2 210 I < Strut nut socket
(Tool No. 31 2 210)