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Date: 04/07/00
To: All Saab Dealers
Saab Service Manager
Saab Parts Manager
Code: 731
Reference: Addressing customer complaint of drifting to one side - All 9-5 Models
To address a complaint of drifting, first:
Make sure that the DOT markings on the tire wall are pointing out. If the tire is directional, make sure the tires are correctly fitted before checking for DOT marking.
Make sure that the tire pressures are correct.
Make sure the car does not have any damage to the chassis. Have any chassis repairs been done?
Make sure that the wheel alignment is according to specification.
It is often believed that a car pulls to one side if it drifts towards the shoulder of the road when the driver lets go of the steering wheel. In most cases, this behavior is not caused by pulling but by a slight inclination of the road towards the shoulder - road crown (curvature of the road surface). The reason all roads have road crown is that the road must cope with all kinds of weather conditions; for example, it must help clear the road of water during a rain storm.
Due to road crown, a vehicle must generate a slight lateral force towards the middle of the road in order to maintain a straight path and not drift towards the shoulder. This lateral force is generated by a tiny steering wheel angle input applied by the driver. The steering angle generates a steering wheel torque that the driver also has to apply to the steering wheel.
If the driver lets go of the steering wheel, the lateral force needed to compensate for the road crown will disappear and the car will start drifting towards the shoulder. The steering wheel will also turn slightly in the direction of the drift. This is completely normal.
Pull to the side, on the other hand, is generated by irregularities in: chassis, powertrain, tires, brakes, etc. and makes the car drift to the left or to the right when the car is driven on a surface without road crown.
If you find that the car pulls to the side, check the car as follows:
Wheel alignment: If toe and camber angles in the front and rear are out of specification, this can cause a problem with the car pulling to one side. Too much toe-in at either the front or rear axles can make the car sensitive to ruts and road crown, causing the car to pull quicker to one side where ruts are present and also where road crown is high.
Tires: If alignment is within specification, swap wheels from the left to the right side at the front first and verify if this causes any changes to the pulling. Then, change the wheels from the left to the right side at the rear. Finally, move the front tires again from the left to the right. Notice if there is any difference and choose the best combination.
Chassis: Put the car on a lift. Check that the front wheels of the car can be turned to their steering end positions with normal resistance. There should be no noise while doing this (no crunching or snapping from the front spring or the upper strut mounting bearing housing.) If any noise is heard, check the axial ball bearing between the upper spring support and the upper strut mount. It should not be damaged or have any oil leakage. If that is the case, the friction between the front strut and the body can cause the front spring to try to pull the front axle either to the left or the right. Make sure the wheels are running easily, i.e., the brakes' rest torque should not be excessive. Brake rest torque difference between left and right side can cause the car to pull to the side. Also check that the chassis bushings are intact. If a bushing is damaged in any way, this can cause geometric changes to wheel suspension geometry which might cause the car to pull sideways.
Steering rack: In some very rare cases, the steering rack power steering valve has been slightly mis-cut. If this is the case the steering rack will force the front axle to turn without the driver applying any torque to the steering wheel. To check this, raise the front end of the car. Position the steering wheel straight ahead and start the engine without holding on to the steering wheel. The steering wheel should remain in the straight ahead position when the engine is running. If it does not, replace the steering rack.
If the car is found to be within specifications and the analysis shows that the car drifts to the side, the solution is to change both front chassis springs. See the table below for old to new part number conversion. Testing has determined that the root cause for a customer complaint of drifting to one side is that the front chassis springs generate internal forces that produce a torque on the front spring strut, causing the car to drift. To determine correct spring application, check the suspension coding found on the VIN plate on the vehicle (located above the left fender toward the A-pillar).
Old P/N New P/N VIN Break
45 66 659 50 62 294 Y3059116
45 66 667 50 62 302 Y3052420
45 66 675 50 62 310 Y3052289
50 56 338 50 62 328 Y3044974
50 62 187 50 62 344 Y3005606
50 62 195 50 62 351 Y3005606
50 62 237 50 62 369 Y3005606
Thank you for your attention.
posted by 12.38.2...
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