Extraneous knocks in the suspension and transmission (Opel Astra J)

If extraneous knocking sounds appear in the suspension of a moving vehicle, it is necessary to immediately determine their source, regardless of whether the knocking is constant or appears only when driving over uneven surfaces.

Warning! Faults in the vehicle's suspension can lead to a serious accident!

Check the suspension according to the procedure described in the Chassis section.

Table 1. Possible causes of knocking in the suspension and ways to eliminate them

Cause	Method of elimination
The shock absorbers are faulty	Replace or repair shock absorbers
The bolts and nuts securing the anti-roll bar are loose; the cushions and rubber-metal hinges of the rod are worn out, the stabilizer struts of the transverse stability are damaged	Tighten the rod mounting bolts; if the rubber cushions are worn out, replace them, replace the damaged stabilizer parts
Damage, deformation of rubber-metal hinges of levers, upper supports of shock absorber struts	Replace the hinges, upper strut mounts
Wear of ball joints of front suspension arms	Replace the ball joints
Increased clearance in wheel hub bearings	Replace the hubs
Large wheel imbalance	Balance the wheels
Wheel rim deformation	Replace the disk
Settling or breakage of the suspension spring	Replace the spring
Wear of rubber-metal hinges (silent blocks) suspension arms	Replace rubber-metal hinges (silent blocks)
Knocking from suspension "breakdown" due to destruction of compression buffers	Replace damaged buffers
Frequent breakdowns of the rear suspension due to overloading of the rear axle	Avoid overloading

Note: It is better to check the condition of the suspension on a car installed on a ramp, inspection pit or lift, and if this is not possible, you can do this work on a free level area, although with less convenience. In any case, you will need an assistant.

It is quite difficult to diagnose the serviceability of transmission components based on the noise they make. If you are unable to accurately determine the source of the noise, contact a qualified specialist.

Table 2. Possible transmission knocks (noises), their causes and methods of elimination

Cause	Method of elimination
Noise when clutch is disengaged
Clutch release bearing worn or lacking lubrication*	Replace the clutch release bearing
Noise when engaging the clutch
Deformation or failure of driven disk parts	Replace the slave disk
Noise in the gearbox
Insufficient oil level	Check the oil level, top up if necessary
Wear, destruction of bearings or gears	Replace damaged parts
Noise when shifting gears
Incomplete clutch disengagement*	Air in the clutch release hydraulic drive or faulty drive units. Bleed the hydraulic drive, replace damaged parts
Synchronizer wear*	Replace worn parts
Wear or failure of bearings or gears	Replace damaged parts
Knocking sound when starting the car
Wear of constant velocity joints	Replace faulty hinges
Increased clearance in the engagement of the main transmission gears	Adjust the gap
Wear of the hole for the satellite axle in the differential box	Replace the differential box
Knocking, clicking when the car is moving in a turn
Wear of the outer constant velocity joint	Replace the faulty hinge