You drive over a speed bump or down a rough road and hear a sharp little "knock-knock" from the front. If you own an Audi A4 or A6, you'll probably know exactly what I mean. Audi A4 and A6 suspension knocking is one of the most common complaints we hear about these cars. And very often, one of the front control arms is to blame. I want to explain why they wear out and how we need to replace them properly, so you're not listening to that same knocking noise again in a few months.
How does the front suspension on the Audi A4 and A6 work?
Many generations of the A4 and A6 have multi-link front suspension. That means several control arms on each side, both upper and lower. They're a big part of why your Audi feels so stable, steers so precisely and rides so comfortably. But! There's a downside. More control arms mean more ball joints and rubber bushes that can wear out over time. And once they do, that familiar knocking from the front begins.
What causes Audi A4 and A6 suspension knocking?
- Worn control arm ball joints – play develops in the joint, causing knocking over bumps.
- Cracked rubber bushes – the control arm starts moving more than it should.
- Hitting potholes and kerbs – these impacts wear out the suspension faster.
- Road salt and water in winter – they damage the rubber boots protecting the ball joints.
How do we find out which control arm is knocking?
We put your car on the lift and check every control arm individually. We look for play in the ball joints and rubber bushes that are cracked or torn. But! Not every knock from the front means a worn control arm. It could be the anti-roll bar bushes, the shock absorbers or the top mounts. That's why we find exactly where the noise is coming from before replacing anything. I don't want you paying for control arms on a guess, only to drive away with the same knocking noise. Because at the end of the day, that money comes out of your pocket, not the garage's.
What's the right way to replace control arms?
- We replace the worn control arms. We usually replace the upper arms in pairs, one on each side.
- We tighten the bolts through the rubber bushes with the suspension at its normal ride height, just as it would be with the car resting on its wheels.
- After the repair, we carry out a wheel alignment. That's one step we never skip.
Pay attention to how the control arm bolts are tightened! If they're tightened while the wheels are hanging in the air, the rubber bushes end up permanently twisted. They then tear much sooner, and the knocking comes straight back. You've paid for new control arms, yet a few months later you're back at the garage again.
Why does it matter so much when the bolts are tightened?
The rubber bushes in the control arms need to sit naturally, without any twisting, when the car is resting on its wheels. If you tighten the bolts while the suspension is hanging down, those bushes stay twisted all the time. Then, every time you hit a pothole and the suspension compresses and extends, they get twisted even further. That's how even a brand-new control arm can wear out in just a few months. And do you know the worst part? There's nothing wrong with the control arm itself. The problem is how it was fitted.
Advice from Kris Mladenov: If you hear knocking from the front, don't wait for it to get louder. A worn control arm isn't just an annoying little "knock-knock". Your tyres suffer too, and the car may behave differently when you brake.
If your Audi A4 or A6 knocks at the front when you drive over potholes or speed bumps, bring it to Das Auto Service. We'll inspect the suspension, find exactly which control arm is worn and replace it properly. Because fitting a new part is easy. What matters is fitting it correctly, so you don't end up paying for the same job twice.
Read more
- Routine servicing at Das Auto Service
- Diagnostics at Das Auto Service
- Shock absorbers: why we replace mounts, caps and dust boots together
- VAG brakes: when should I replace brake discs and pads together?
- Audi A4 B8 2.0 TDI service schedule
- Wheel bearing: a humming noise that gets louder with speed
- Electric steering rack on the Golf and A3: knocking and fault codes
Frequently asked questions
Why do the control arms on my Audi A4 knock?
Usually, it's worn ball joints or damaged rubber bushes. Multi-link suspension has more of both, which means more places where play can develop.
Should control arms be replaced in pairs?
Usually, yes. Both sides tend to wear at roughly the same rate, so we normally replace them in pairs.
Do I need wheel alignment after replacing control arms?
Yes, absolutely. We always carry out a wheel alignment after replacing control arms.