Eliminating Front End Vibration

Steering wheel shimmy at certain speeds is generally caused by wheel imbalance.

• Check the tyre pressure and correct it if necessary.

• Carry out a road test. Narrow down the fault as precisely as possible: speed range, road surface, cornering or straight-line driving.

• Raise the vehicle.

• Check the wheel centering on the hub. The hub or brake drum must protrude beyond the wheel's centre flange, or at least be flush with it. Otherwise, replace the wheel rim.

• Check the suspension. Check the rubber-metal bushings, joints, shock absorbers and wheel rims for proper condition.

• Remove and clean the wheels. For example, also remove any stones from the tread.

• Inspect the tyres for flat spots. These are areas of reduced tread depth that can occur during emergency braking when the wheels lock.

• Check the tread depth of each tyre and compare them. If the tyres show abnormal wear at the front and/or rear, the vehicle must be wheel-aligned at the front and rear and adjusted if necessary. Set the toe-in to the upper tolerance limit. Note: wheel alignment requires suitable measuring equipment, which is usually only available at a specialist workshop.

• Carry out a road test and check whether the faults are still present.

Check the radial and lateral runout of the wheels.

• With the vehicle raised on stands, place a suitable dial gauge on the tread, then on the tyre sidewall.

  Turn the wheel slowly by hand, read the dial gauge deflection, and mark the point of maximum radial runout on the tyre with chalk.

Nominal values: maximum radial runout = 3 mm; maximum lateral runout = 3 mm.

• If these values are not met, balance the wheels on a stationary balancing machine. The wheels must be centred in the same way as on the vehicle. Conical clamping devices that centre the wheel in the centre bore are not permitted.

  The permissible residual imbalance on both balancing planes is 5 grams.

Eliminating radial runout (match-mounting):

• Release the air from the tyre and press the tyre beads into the well of the rim.

• Rotate the tyre 120° on the rim.

• Inflate the tyre and check the radial runout again.

• If the maximum value is exceeded, rotate the tyre a further 120° on the rim and check the radial runout.

• If the maximum value is met, balance the wheels.

Check the radial and lateral runout of the wheel rim.

• Mount the rim without the tyre, centred, on the balancing machine or on the vehicle. Fit the dial gauge.

• Check the radial and lateral runout of the wheel rim. Radial runout (out-of-round) is measured at the rim flange, and lateral runout (side runout) at the flat side surface of the rim flange. Disregard isolated dial gauge deflections caused by raised or recessed areas in the material.

Nominal values: maximum radial runout = 3 mm; maximum lateral runout = 3 mm.

• If the nominal values are exceeded, replace the wheel rim.

• With the vehicle raised on stands, position the wheels so that the point of maximum radial runout is at the top.

  In this position, tighten the wheel bolts in a crisscross pattern with a torque wrench to 90 N·m.

• Carry out a road test. If front-end vibration or steering wheel shimmy is still present, the cause may be residual imbalance, which can be eliminated by rebalancing on the vehicle.

Rebalance or balance the wheels on the vehicle.

• When balancing drive wheels, always place both tyres of one axle on roller stands (drive rollers).

• The wheels must be driven by the vehicle engine so that the wheels rotate synchronously.

• Carry out a road test.

If faults still occur, the radial or lateral runout of one or more tyres is too high. This cannot be measured with workshop equipment.

In this case, the only remedy is to replace the front and/or rear tyres. As a rule, tyres should always be replaced in pairs.