The BMW E46 was the best selling generation of the 3 Series. And while the rear-wheel-drive sports sedan is one of the more complicated cars to align, it offers many service and repair opportunities.
The front suspension is a strut design with the familiar sickle-shaped control arm that was introduced on this platform in 1983. The rear suspension carried over from the E36, but it has a unique rear trailing arm design.
The best advice given by many BMW dealership technicians is to measure the ride height before starting an alignment. The rear suspension is sensitive to changes in both front and rear heights. BMW specifies the ride height must be within ±2mm. The measurement is taken between the lip of the wheel well and the bottom of the rim. The specifications vary between coupes, sedans and suspension packages, so be sure to check your service information for the right spec.
The number one component to fail on the BMW E46 front suspension is the rear control arm bushing. The bushing is attached to the unibody, directly next to the driver and passenger foot wells. When this bushing gets soft, it will change the toe, camber and caster. This will result in inside edge tire wear.
Camber can be adjusted ±0.5º by moving the upper strut mount in slots cut in the strut tower. If you cannot get the camber into spec with this adjustment, start looking at the ride height, bushings and cradle. Other more radical camber adjustment kits are available that can change the camber by -3.5º, but these are for track-day cars.
Adjusting the toe is the same as on any other vehicle. BMW makes it easier with marks on the steering rack and shaft. If the toe is adjusted properly and the marks match up, you should not have to recalibrate the steering angle sensor. But, the output for the steering angle sensor should be checked with a scan tool to make sure it reads that it’s centered. If a tie rod or the rack is replaced, the sensor must be recalibrated. In addition, the steering angle sensor must be coded or reflashed if it has been replaced.
‘C’ ARM-TYPE REAR SUSPENSION
The rear suspension on a BMW E46 is very unique. The design is called a “C” arm type. BMW calls it an “Elastokinematics” suspension system that is designed to be pliable (like elastic), which absorbs the longitudinal and axial forces of driving to provide better handling characteristics. But, the rear has more than a dozen mounts and bushings that can soften and eventually fail. This can result in noise and a change in the alignment angle.
The design may seem complex, but the engineers at BMW designed the trailing arm and links to change camber and toe as the vehicle rolls and squats. This is why measuring the ride height before the alignment is critical.
The differential is mounted to the subframe using a hydraulic mount. The subframe is mounted to the body at four vibration-absorbing rubber mounts. The upper transverse control arms are made from cast aluminum for weight saving.
Some drivers may complain of a pulling during acceleration and braking, which could be linked to worn bushings.
A change in camber also corresponds to a change in toe, so this means that camber must be adjusted first. Camber is adjusted using an eccentric bolt on the lower control arm. If the collar nut is tightened more than 10 times during adjustment, it must be replaced because the self-locking effect becomes too slight.
Toe is adjusted by changing the position of the plates that connect the trailing arm to the body, which is called a bearing pedestal. Release the screws 1-1/2 turns at the bearing pedestal and attach special tool 32 3 030 to screw the head to a notch in the plate. Turn the special tool and adjust toe-in to the specified value.
REAR AXLE CARRIER ISSUES
Under certain circumstances, a fracture in the steel body structure could form in the area around one of the rear axle carrier mounting points. As a result, a distinct clicking noise can be heard from the area of the rear axle carrier during certain driving conditions. Specifically, the noise may be heard during load reversals on the rear axle, such as when starting from a stop, engaging forward or reverse gears, or when rapidly changing gears.
As a result of the proposed settlement of a class action lawsuit, a national subframe inspection and repair program has been developed. Under this program, any current owner of a U.S.-specification E46 3 Series car may have his or her E46 inspected to determine whether any damage to the rear axle carrier support is present. If damage to the rear axle carrier support is found during the inspection, and the vehicle qualifies for the repairs, BMW will repair the vehicle using one of two approved repair procedures: either a structural epoxy repair or replacement of the rear axle carrier, depending on the evaluation of the damage.