Table of Contents E83 Chassis Dynamics Subject Page Purpose of the System .3 E83 Chassis Dynamics.3 System Components.3 Front Axle Mechanical Components. Technical Data . Workshop Hints . Alignment and Camber Adjustment . Strut Replacement . Spring Replacement. Reinforcement Plate. Rear Axle. Technical Data . Workshop Hints . Adjustment of Rear Wheel Alignment. Lowering (removing) the Rear Axle . Brakes. Mechanical Components. Hydraulic Unit with Vacuum Brake Booster and DSC Hydraulic Module . Foot Controls with Brake and Clutch Pedals. Parking Handbrake Lever, ASZE, Cables and Duo-Servo Brakes. Workshop Hints ... Changing Cables Steering .9 Wheels and Tires.10 Tire Deflation Warning (RDW).11 Initial Print Date: 10/03 Revision Date: co^r^LOLOLnLnLo ld co co co co h- cococococo Chassis Dynamics Model: E83 Production: Start of Production MY 2004 ■BIIBTHBS After completion of this module you will be able to: • Visually identify the suspension components that are unique to the E83 • Describe the steering system mechanical/hydraulic components • Demonstrate how to access, remove and install the spare wheel • Explain how to initialize RDW 2 E83 Chassis Dynamics Purpose of the System E83 Chassis Dynamics As with all BMW vehicles, the X3 chassis and suspension was designed with particular emphasis on driving pleasure, dynamics and favorable handling. The main aim in the full development of the X3 was to achieve: • Agility on the road • Driving dynamics • Stability • Traction The front axle is a double joint spring strut axle with tension arms and a rack and pinion steering system with hydraulic power assist. Conventional rack and pinion power steer¬ ing is installed to the E83 as standard. Servotronic is available as an option. Spring struts with coil springs and twin tube gas-pressure dampers are used on the front axle. It is similar the front axle of the E53. The rear axle design is based on the E46/16 with barrel springs and separate twin tube gas-pressure dampers. The brake system is a hydraulic dual-circuit brake system with "front/rear split" vacuum boost power assist and EBV. The parking brake actuating unit is located in the center console and is eguipped with an automatic cable adjuster (ASZE) and a compensating element. Several different wheel and tire combinations are available for the E83. The spare wheel (steel) is located in a special bracket under the luggage compartment floor in the rear. The tire deflation warning (RDW) is a standard feature on the E83. System Components Front Axle Specific components in the E83 (subject to additional load) are designed as forged steel parts. • Control arms: forged steel with rubber mount • Tension arms: forged steel with hydraulic bushing • Swivel bearing: forged steel, track arm forged on 3 E83 Chassis Dynamics A reinforcement plate (thrust panel) is bolted to the front axle carrier. This makes a contri¬ bution to the rigidity of the front structure and suspension. There are two recesses in this thrust zone for accessibility to the engine oil drain plug (rectangular recess on 6 cylinder engines). Mechanical Components 1. Swivel bearing 2. Anti-roll bar link (attached to strut tube) 3. Thrust panel 4. Control arm 5. Tension arm 6. Anti-roll bar 7. Front axle carrier 8. Axle carrier rear mounts Technical Data Wheels 7Jx17 8Jx17 8Jx18 Tires 215/60 235/55 235/50 Rim offset (mm) 39 46 46 Track width (mm) 1,537.7 1,523.7 1,523.7 Total toe-in 6°± 10' 6°± 10' 6°± 10' Min. camber -20' ± 20' -20' ± 20' -20' ± 20' Camber differential angle max. 30' left to right max. 30' left to right max. 30' left to right Caster offset (mm) 25.79 25.79 25.79 Kingpin offset (mm) -0.88 -7.88 -8.53 Toe difference angle 2° 16'±30' 2° 16'±30' 2° 16'±30' Steering axis inclination angle 12° 41' ±30' 12° 41'±30' 12° 41' ±30' Caster angle 5° 47'±30' 5° 47' ±30' 5° 47' ±30' Caster angle differential max. 30' left to right max. 30' left to right max. 30' left to right Maximum steering angle internal 38° external 31 0 internal 38° external 31 0 internal 38° external 31 0 4 E83 Chassis Dynamics Workshop Hints Alignment and Camber Adjustment Toe-in adjustment is performed at the tie rods. If necessary, the camber is corrected by driving out the pin on the strut tower (spring cup). Strut Replacement When replacing the strut, the mounting on the swivel bearing must be expanded with a special tool. Spring Replacement There are new spring tensioners to be used during spring replacement. Refer to Repair Instructions for detailed information about special tools. Reinforcement Plate The vehicle must not be driven without the reinforcement plate in place. The reinforce¬ ment plate ensures the transversal rigidity and contributes to the strength of the front axle. Rear Axle The E83 is fitted with a central rear axle and subframe. The design of the rear axle is similar to the E46/16. Two tension arms have been added to the rear axle of the E83 and are secured to the bodyshell. Mechanical Components 1. Tension arm 2. Trailing arm 3. Upper control arm 4. Rear axle bracket 5. Lower control arm with plastic cover 6. Thrust brace 5 E83 Chassis Dynamics TF03-3625 Modifications to the E46/16 rear axle to adapt it to the E83: • Anti-roll bar secured to the rear axle carrier by clamps. • Front of rear axle carrier suspension converted to special bolts with additional thrust washer. • Thrust brace and tension arms. • Surface of control arms are galvanized steel plates. • Anti-roll bar link with ball joint attached directly to the control arm. • Dampers with three point flange (bolt) plate. Technical Data Wheels 7Jx17 8Jx17 9Jx18 Tires 215/60 R17 235/55 R17 255/45 R18 Rim offset (mm) 39 46 51 Total track width (mm) 1,611 1,611 1,611 Total toe-in 6° ±8' 6° ±8' 6° ±8' Camber -2° ±15' -2° ±15' -2° ±15' Thrust angle 0° ± 4' 0° ± 4' 0° ± 4' Workshop Hints Adjustment of Rear Wheel Alignment Rear wheel alignment is adjusted by a special tool on the lower trailing arm (refer to Repair Information for additional details. The camber is adjusted by an eccentric element on the lower control arm at the axle carrier connection. Lowering (removing) the Rear Axle The handbrake cables (routed through the rear axle carrier and the body console) must be disengaged before the rear axle is lowered. This is to prevent shearing of the hand¬ brake cables. 6 E83 Chassis Dynamics Brakes The brake system is a hydraulic dual-circuit brake system with "front/rear split", vacuum boost power assist and EBV. One brake circuit each for the front and rear axles. The parking brake actuating unit is located in the center console and is eguipped with an automatic cable adjuster (ASZE) and a compensating element. The advantages of the parking brake with automatic cable adjuster are: • The 2 cables no longer have to be adjusted during installation. • Cable extensions (cable conduit) contractions over the operating time are automati¬ cally compensated so that the parking brake lever travel is consistent. • Prestretching of the cables is no longer necessary. • The parking brake does not have to be adjusted at the end of the assembly line and in the service department. • Note: color coded handbrake cables (left/right different part numbers). Mechanical Components The brake system consists of the following components: 7 E83 Chassis Dynamics Four Wheel Hydraulic Disc Brakes The front brakes are constructed of ventilated brake discs 325mm diameter x 25mm thick (Geomet coating) with FN57/25 single piston floating calipers. The rear brake brakes are constructed of ventilated brake discs 320mm diameter x 22mm thick (Geomet coating) with FN42/22 single piston floating calipers. Hydraulic Unit with Vacuum Brake Booster and DSC Hydraulic Module The hydraulic unit is located at the front on the left hand side under the main brake cylin¬ der. The electric precharging pump is no longer reguired. All vehicles are eguipped with an 879" tandem brake booster and have a tandem brake master cylinder. The DSC hydraulic module is a DSC8 system. Foot Controls with Brake and Clutch Pedals The essential components of the foot controls are: • Pedal mounting block • Brake pedal • Clutch pedal • Clutch master cylinder The pedal mounting block is made of aluminum and is bolted to the bulkhead. The vehicle has a wide steel brake pedal. The clutch pedal is made of plastic. Parking Handbrake Lever, ASZE, Cables and Duo-Servo Brakes. The duo-servo brakes are similar to the duo-servo brakes on the E65 and E53 (185mm diameter x 30mm wide). The handbrake lever is bolted to the floor pan and is eguipped with an automatic cable adjuster (ASZE) and a compensating element. Refer to ST045 E85 or ST047 E60 Technical Training handouts for additional details on deactivating and activating this unit. Workshop Hints Changing Cables If there is a broken cable, the automatic cable adjuster is in the untensioned position. To replace the cables, it is necessary to remove the center console and the rear compart¬ ment ventilation ducts. For the cables to be removed or parking break shoe replacement, the parking-brake lever must be in the released position and the ASZE unit must be deactivated. Refer to the Repair Instructions or ST045 E85, ST047 E60 Technical Training handouts for additional details. 8 E83 Chassis Dynamics Steering Conventional rack and pinion power steering is used in the E83 and Servotronic is avail¬ able as an option. The design and functioning principle of the Servotronic option are nothing new but have been modified as described in this chapter. The servotronic steering system controls the amount of power assistance based on the current road speed. The hydraulic pressure is electronically adapted to the current road speed, with greater power assistance available at lower road speeds and less power assistance available at greater road speeds. Mechanical/Hydraulic Components 1. Power-steering cooler 2. Hydraulic pump with supply reservoir (M57TU, diesel) 3. Servotronic control unit 4. Upper steering column assembly 5. Flexible hoses 6. Steering gear 7. Hydraulic pump with separate supply reservoir (M54B25 and M54B30) The E83 is eguipped with hydraulic assisted rack and pinion steering. The total ratio of the steering is: 18.9 : 1. The total rack stroke is 81.0 mm (1.7 turns of the steering wheel). The hydraulic ports on the steering gear have guick release couplings. The hydraulic pump maximum pressure is limited to 127 bar. E83 vehicles are eguipped with “W” shaped cooling loops (hoses) to assist in cooling. CAUTION!!! The hydraulic pump does not have a pump end shutdown feature. The hydraulic pump could be damaged after approximately 1 minute if the steering is kept on full lock (end stop) for a long period. 9 E83 Chassis Dynamics Wheels and Tires Several different wheel stylings are available. Different 17" wheel stylings are standard equipment. Other 17" and 18" wheels are available as options, depending on the type of engine. A compact wheel (spare/emergency wheel) is standard, regardless of the vehicle version. The tire deflation warning (RDW) is a standard feature. The RDW function is integrated in the DSC control unit. The following wheel/tire combinations are available for US models: 2.5Liter Engine (optional for 3.0 Liter) • 8.0Jx17 EH2 IS46* (shown to the right) • 235/55 R17 LI 99** tires • A/S • H-rated tires, M+S 3.0 Liter Engine (optional for 2.5 Liter) • 8.0Jx17 EH2 IS46* (shown to the right) • 235/55 R17 LI 99** tires • A/S • H-rated tires, M+S Optional (for 2.5 and 3.0) • 8.0Jx18 EH2 IS46* (shown to the right) • 235/50 R18 LI 97** tires • A/S • H-rated tires, M+S Optional (for 2.5 and 3.0) • 8.0Jx18 EH2 IS46* (shown to the right) • 235/50 R18 LI 97** tires • A/S • H-rated tires, M+S * IS = insert size ** LI = load index A = all season tires S = summer tires 10 E83 Chassis Dynamics The spare/emergency wheel (compact wheel) is standard equipment. The E83 has a special bracket for the compact wheel which is located in the vehicle floor under the luggage compartment and is operated from inside the vehicle. The release knob is located under the luggage compartment floor covering next to the tool kit. The compact wheel is a 4Bx17 IS18 steel wheel with T135/90 R17 104 M tire. The compact wheel bracket has a special ser¬ vice access cap (1) to check the tire pressure without having to lower the bracket/wheel. Tire Deflation Warning (RDW) The RDW function is integrated (and diagnosed) in the DSC control unit. The system uses the rotation speed of the diagonally opposite wheels to compare the dynamic cir¬ cumferences of all four wheels. The RDW system does not monitor uniform air pressure loss over all 4 tires. If the pres¬ sure loss is the same in all four tires, the wheel speeds change equally and pressure loss cannot be detected. The customer must continue to check inflation pressures on a regu¬ lar basis. The system must be reinitialized if tire inflation pressures are modified or if the tires/ wheels are replaced. Initializing RDW: 1 .Start the engine but do not drive away. 2. Press and hold the RDW button in the center console until the indicator light in the instrument cluster illuminates in yellow for several seconds. 3. Drive away. After a certain distance, the system stores the new wheel speeds as reference values and is then able to display a detected deviation. RDW has an indicator light in the instrument cluster that may illuminate in yellow or red. Indicator illuminates in red: • Indicates a loss of more than 30% of inflation pressure in one of the tires • Accompanied by a “gong” sound Indicator illuminates in yellow : • Possible faults in the system • Initialization (D (D 11 E83 Chassis Dynamics