Road Test. Chevrolet Metro 1998

For 1990-2009 cars

### Tire and Wheel Inspection

The tires on all new GM models have a tire performance criteria (TPC) rating number molded on the sidewall. The TPC rating will appear as a four-digit number preceded by TPC SPEC on the tire wall near the tire size. A replacement tire should have the same TPC rating.

(1) | Hard Cornering, Under Inflation
(2) | Excessive Toe on Non-Drive Axle
(3) | Heavy Acceleration on Drive Axle, Excessive Toe on Drive Axle, Over Inflation

This test should be performed for ALL vibration complaints unless the disturbance occurs only with the vehicle at a standstill.

Inspect the tire and wheel assemblies for the following conditions:

• | Unusual wear such as cupping, flat spots, and heel-and-toe wear

| (These conditions can cause tire growl, howl, slapping noises, and vibrations throughout the vehicle.)

• | Proper inflation

• | Bulges in the sidewalls

| (Not to be confused with normal ply splices, commonly seen as indentations in the sidewall.)

• | Bent rim flanges

Inspecting these characteristics of the tire and wheel assemblies may lead to the cause of the vibration. At the very least, the inspection will provide assurance that the vehicle is safe for road testing.

### Slow Acceleration Test

This test will identify the engine-speed or vehicle-speed related conditions. Additional tests may be necessary in order to determine in which category the vibration belongs.

1. Observe the necessary safety precautions. Refer to

   Caution: Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could lead to serious personal injury and vehicle damage.

   in Cautions and Notices.
2. On a smooth, level road, slowly accelerate up to highway speed.
3. Look for disturbances that match the customer's description.
4. Note the following readings where the disturbance occurs:

• | The vehicle speed, km/h (mph)

• | The engine speed (RPM)

• | The frequency (if possible)

Following this test, perform the Neutral Coast-Down Test and the Downshift Test.

### Downshift Test

1. Observe the necessary safety precautions. Refer to

   Caution: Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could lead to serious personal injury and vehicle damage.

   in Cautions and Notices.
2. On a smooth, level road, accelerate to the speed at which the complaint vibration occurs.

Note the engine RPM.

3. Decelerate and safely downshift to the next lower gear (from OVERDRIVE to DRIVE, or from DRIVE to SECOND, etc.)
4. Operate the vehicle at the previous engine RPM.

If the vibration returns at the same engine RPM, the engine or the torque converter are the most probable causes. You may repeat this test in still smaller gears, and in NEUTRAL, in order to confirm the results.

In some cases, a vibration may be sensitive to torque or engine load, as well as being related to a specific engine (RPM) or vehicle (km/h/mph) speed. These vibrations can be most difficult to diagnose, and require additional testing. Still, following a systematic approach usually leads to pinpointing the problem.

### Neutral Run-Up Test

This test is designed to identify engine-speed related vibrations. Use this test when the customer complains of vibration at idle, or as a follow-up to the downshift test. This test more than likely doesn't apply when the complaint is vehicle-speed related only (appearing at the same vehicle speed regardless of the engine speed).

1. Observe the necessary safety precautions. Refer to

   Caution: Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could lead to serious personal injury and vehicle damage.

   in Cautions and Notices.
2. Slowly increase the engine speed while looking for disturbances that match the customer's complaint.
3. Note at which engine speed (rpm) and frequency (if possible) that the vibration occurs.

### Brake Torque Test

This test is designed to identify engine-related vibrations that were not uncovered with the Neutral Run-Up Test. This test also works for vibrations that are sensitive to the engine load or to the torque. This test will more than likely not apply to vehicle-speed related only vibrations.

1. Observe the necessary safety precautions. Refer to

   Caution: Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could lead to serious personal injury and vehicle damage.

   in Cautions and Notices.
2. Apply the parking brake.
3. Block the front wheels.
4. Step firmly on the brake pedal.
5. Place the vehicle in Drive.

Caution: One or more of the following guidelines may apply when performing specific required tests in the work stall:

• | When a test requires spinning the drive wheels with the vehicle jacked up, adhere to the following precautions:

- | Do not exceed 56 km/h (35 mph) when spinning one drive wheel with the other drive wheel stopped. This limit is necessary because the speedometer indicates only one-half the actual vehicle speed under these conditions. Personal injury may result from excessive wheel spinning.

- | If all of the drive wheels are spinning at the same speed, do not exceed 112 km/h (70 mph). Personal injury may result from excessive wheel spinning.

- | All persons should stay clear of the rotating components and the balance weight areas in order to avoid possible personal injury.

- | When running an engine in the repair stall for an extended period of time, use care not to overheat the engine and the transmission.

• | When a test requires jacking up the vehicle and running with the wheels and brake rotors removed, adhere to the following precautions:

- | Support the suspension at normal ride height.

- | Do not apply the brake with the brake rotors removed.

- | Do not place the transmission in PARK with the drive axles spinning.

- | Turn Off the ignition in order to stop the powertrain components from spinning.

• | When running an engine in the work stall, use the exhaust removal system to prevent breathing dangerous gases.

6. Slowly increase the engine speed while looking for vibrations that match the customer's description.
7. Note the engine speed (rpm) and frequency (if possible) at which the disturbance occurs.
8. Repeat steps 3, 5, and 6 in Reverse, if necessary.

### Additional Tests

You can perform one or more of the following tests for unique vibration complaints such as those that are torque/load sensitive, in addition to vehicle-speed or engine-speed sensitive:

• | Steering Input Test

• | Standing Start Acceleration Test

### Steering Input Test

This test is intended to determine how much the wheel bearings and other suspension components contribute to the vibration, especially those relating to noises such as growl, grinding, and roaring.

Caution: Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could lead to serious personal injury and vehicle damage.

1. Observe the necessary safety precautions.
2. Drive through slow sweeping turns with the vehicle at the vibration speed (mph) in one direction, then in the other.
3. If the vibration gets worse or goes away, inspect the following components as possible causes of the vibration:

• | The wheel bearings

• | The hubs

• | The tire tread

### Standing Start Acceleration (Launch Shudder) Test

The purpose of this test is to duplicate a vibration called launch shudder. In some cases, a powertrain mount or an exhaust ground-out may also be suspected, depending on the symptoms.

Caution: Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could lead to serious personal injury and vehicle damage.

1. Observe the necessary safety precautions.
2. With the vehicle at a complete stop and in gear, remove your foot from the brake pedal.
3. Accelerate to 48-64 km/h (30-40 mph) while looking for vibrations that match the customer's description.

Other possible causes of launch shudder include the following conditions:

• | Incorrect trim height. Refer to Trim Height in Suspension General Diagnosis.

• | A worn or damaged drive axle CV joint.

• | A ground-out engine/transaxle mount.

• | Faulty exhaust hangers and mounts.