Persistent knocking - diagnosis elusive
 

Hi Everyone

I have a 2005 A8 quattro SE 3.0 Tdi which is excellent in every aspect except for a persistent knock from I suspect the front suspension, or second guess the gearbox/engine mounts. I have had it checked out by two different specialists to no avail.

If we were in the 1960’s or 1970’s it would be easy to diagnose as it sounds just like the exhaust knocking on bodywork when a strap has broken. It isn’t that though.

The car is due an MOT which it will pass as there is no play, or worn parts, no air leaks and the suspension operates on all levels. There are no fault codes using VCDS either

It has been suggested I have a “lazy” nearside front strut and replacing it might solve the issue. I think it is false economy changing one so I would change both sides and this leads me to the next dilemma. I can get Aerosus exchange “bags” at a fair price or Chinese manufactured ones also at a reasonable price, both with two-year guarantees.

I am not adverse to buying either, I just want the best option so any positive comments would be appreciated.

This with fitting, which I am not capable of doing myself (not a technician, no tools, no inclination and no self-confidence) means a budget of £1,000 and not a cast iron assurance that this will cure it. This makes it a gamble.

I like my cars to be as they left the factory so I do not want upgrades, go faster spec, lowered, widened or stiffened anythings bolted on. I simply want this knock resolved.

The alternative is to sell it and buy a D4, but I could conceivably spend another £7000 (minimum) and be faced with another set of elusive issues as with my buying power I would be looking at an eight-year-old car.

So, the other man’s grass may not be any greener.

What I am hoping for, is some advice, suggestions, recommendations or an offer to solve this. This cannot be the only D3 with this noise

It is annoying because apart from this knocking, which resembles a persistent door-to-door salesperson hoping to sell me Betterware, Avon, or eternal salvation, the car is great.

Any help would be appreciated

If the knocking is coming from a strut then its the damper portion of it, not the airbag, so changing the bags won't do anything. You'd need a good used strut assembly instead (Prestige have a D3 in at the mo I think).

Thanks, that is great advice it never occurred to me to just change the strut and keep the rest. I will investigate....

I would have a look at the sway bar links.

I noticed massive decreases in clunking after changing these shortly after I changed the upper control arms.

Unfortunately, the knocking came back so I was gearing up to check the struts. Until i looked under the car and found the sway bar link bolt in the bar had sheared off. Removing the sway bar completely (until the new one comes from germany) and taking the car for a drive eliminated all suspension noise on my car.

Mike

Thanks again for your suggestions. The sway (anti-roll bar) has been taken off completely and road tested and the knocking was still there. The car is being MOT’d on Tuesday 20th and having driven the car a few times since I started this post I am coming to the conclusion that it is predominantly the nearside front strut that is the source.

I am very likely going to invest in a front pair of struts as apart from this fault the car is excellent.

I have had D2’s previously, the best being a 3.7 quattro and although a D4 is an attractive proposition they do not look to me somehow as sleek and poised as their predecessors.

I will update the post in the next few weeks, thanks

Hi Paulyrow, did you get around to replacing the struts? Is the noise gone? Cheers.

Why not just buy the offending corner?

^^This. Unlike normal springs, you can replace just the one corner

If there was anything wrong with the shock I would still be tempted to replace both sides.

That being said the fault has not been diagnosed and I would not be throwing huge amounts of money at the problem replacing parts and hoping that it will cure the it. I don't think you get many issues with struts other than air leaks either bag, o-rings or residual pressure valves all of which could be replaced for a lot less money than whole strut.

For all we know it could be lost nut, screw or socket rolling around somewhere making the noise. If it was me I would leave it alone and live with it after verifying that it is not something that affects safety.