You replace the dampers to get rid of a knock or float — and a new knock sounds from under the wheels that was not there before. Annoying, but so typical that it has a short list of causes: in the vast majority of cases the fitting or the economised “small parts” are to blame rather than the dampers themselves. Here is that list, from common to rare.
Fitting mistakes are cause number one
The most widespread is tightening the rod nut with an impact gun. The damper rod spins, its seat in the top mount is damaged, and the torque ends up random. The correct method is to hold the rod with a separate spanner and tighten the nut to torque. An under- or over-tightened nut gives a clear knock from the top of the strut on every bump.
Other typical slips:
- the spring did not seat in its proper location during assembly — a knock and creak when the car is rocked;
- the strut-to-knuckle bolts or the top mount nuts are not tightened;
- spacers and washers from the mount kit are mixed up or forgotten.
All of these are cured by re-torquing and reassembly — quick, and under the labour warranty.
Economising on mounts and bump stops
A damper works inside its hardware: above it the top mount and its bearing, on the rod the bump stop and the boot. Manufacturers recommend replacing that hardware with the damper. If a new strut received an old sagged mount or a crumbled bump stop, a knock is almost guaranteed: the mount passes impacts into the body, and without a bump stop the suspension bottoms out with a hard metallic strike — see signs of worn bump stops.
The strut top mount bearing is its own story: its wear is heard not only over bumps but when the steering is turned while parked, as covered in a noisy strut top mount bearing.
When the part itself is to blame
Faulty and counterfeit parts exist, especially for popular brands. The signs: a knock from the first days with correct assembly, oil weeping on the body, different firmness left and right. It is checked simply — by swapping sides or replacing under warranty. The genuine defect rate at established manufacturers is low, so this version is checked after the fitting ones.
| Symptom | Likely cause | What to do |
|---|---|---|
| Knock from above over small bumps | Rod nut, top mount, bearing | Re-torque, replace the mount |
| Hard impact in deep potholes | Missing or destroyed bump stop | Complete the strut hardware |
| Knock and creak when rocked | Spring not seated, dry bushes | Reassemble the strut |
| Knock from the first kilometres, oil weeping | A faulty damper | Warranty replacement |
| The knock existed before and got louder | A neighbouring component | Diagnosis |
When the dampers are not involved
There is a third scenario: what knocks is not what was replaced. Strut work almost always means undoing the anti-roll bar links, and a seized joint is easily damaged in the process. Or more simply: new, firmer dampers changed the suspension’s behaviour, and wear in a neighbouring component that was previously masked by float has become audible. You can check that yourself — the method is in finding a suspension knock without a lift, and the typical sounds are on the symptom pages knocking in the suspension and knocking over bumps.
The order of action
A sensible sequence:
- Drive 300–500 km and return to the workshop for a check re-torque — normal practice, not a complaint.
- If the knock remains, ask for the rod nut torque and the state of the mounts and bump stops to be checked on a lift.
- Disputed cases are settled by an independent diagnosis.
The conversation with a workshop is easier when there is a work order and a clear history: what was replaced, when the sound appeared. The wider version of that conversation is in a knock after suspension work: who is to blame.
To keep it specific, capture the knock itself: record it in the Pro-Stuk app on the same stretch of road where it is heard best. The algorithm matches the recording with your answers and shows the likely causes with an urgency level — with a recording it is harder for a workshop to say “everything is fine”.
