Small knocking noise C5 III Tourer

[fifth_cit]

Hi All, My C5 III tourer (Steel Suspension) has developed a small knocking or clunking noise when I brake or accelerate, which I can feel through the steering wheel and seems to be on the drivers side. It isn't bad or violent more annoying than anything else.
Sadly car is no longer under warranty so I will have to get my hands dirty.
Any ideas ?

[davewithington]

Could be the drop link. Doesn't need much play to feel and sound horrendous.

[BrianM]

Passenger side drop link has been replaced on mine - mind you didn't notice anything but was done at last service.

Brian
09 C5 Exclusive

[fifth_cit]

Thanks for the replies, how can I tell if it is a drop link that has failed ? I haven't felt any knocking going over bumps or speed ramps, only when braking accelerating and reversing to park etc. Keith

[xantia_v6]

If the knock is on brake and accelerate, I would look first at the engine mounts.

[Richard_C]

I had a similar hard to find knock on my SAAB 9-5, the answer was the drop link. Similar anti roll bar layout to the C5. Took me a good few weeks to work it out. Maybe this will help your diagnosis. Apologies if you know all this already but it might help others.

The drop links (one each side) join the transverse anti roll bar to the lower parts of the suspension. They work hardest when the car is trying to roll around its longditudinal axis. If you go over a sleeping policeman type speed bump dead square on, both sides of the suspension move as if in unison, the anti roll bar rotates in its mounts but exerts no corrective force; the drop links have little work to cope with. You might get a small knock if one is badly worn. If you go over the hated and unnecessary pillow type speed bump, one side of the suspension goes up, the other doesn't, the anti roll bar twists and the drop links get more work to do. That is when you hear them. Because they work one against the other, it doesn't matter which side of the car goes over the bump, both drop links are working hard so the clunk will appear. Say the right hand drop link is worn: bump on right, knock on right, bump on left, knock on right still. Once clunked, it stays clunked (makes no more noise) until the loads are reversed and the anti roll bar relaxes - so the symptom is 'two clunks per manouver' not one per wheel rotation or whatever.

You tend not to hear the knock at speed, too much noise from everything else, but you would typically hear/feel it when pulling away or starting a reverse with the steering turned, braking to turn into the drive, bumbling slowly through potholes on one side only, or stop start braking at low speed in a tight turn, like queuing down a car park exit spiral.

If the knock is when you accelerate or brake in a straight line, then the engine mount suggestion may be your first stop. If it happens whilst wiggling about, drop link is favourite.

Maybe if the wind and hail stops you can do a few low speed manouvers with the window open and your ear extended. An alternative is to fix a friend to each wing using a few rolls of duck tape and ask them where they think the noise is coming from.

Do let us know what the answer is. I have a CIII Tourer (bought with 19k miles on it) now and am building my knowledge base for the future, I tend to keep cars for 100k miles or so.

[fifth_cit]

Thank you Richard_C for your comprehensive reply.

It is definitely more apparent when you are doing slow turns reversing etc so I will go down the drop link route.

This started about 18 months ago and was "fixed" at its 2 year service by Citroen by "Giving everything a good torquing up". I noticed it again in June last year and took it in but they said they could not find anything wrong and to be truthful the problem went away but has returned just recently. The noise started at about 18,000 miles and the car has now done just over 31,000 miles and has always been more apparent in dry weather.

Lots of sped bumps of every design around where I live so I will approach them with the window down and have a listen.

Keith

[davewithington]

I replaced both drop links about 18 months ago, and I have a problem with the right hand link again, at this moment - due for replacement this weekend.

It appears that either the thread in the nut or on the link has partially stripped, allowing about 1mm clearance. I've added another locknut pro tem. This is not uncommon according to my repairer friend. Buying top quality links is the only answer long term.

[fifth_cit]

Has anyone got the torque wrench settings for these drop links or point me to a place where I can get them.
Keith

[CitroJim]

Just do them up sensibly tight. Not FT but moderately tight. I use a good lean on an 18mm ring that's about 10 inches long overall.

[Richard_C]

Ah - the "good lean".

Assuming the operator weighs 10 stone and the good lean exerts about half of their body weight on a 10 inch spanner, that looks like 58.33 lb/ft (my generation) which I think is about 8 Kg/m (later generation). Not to be confused with the "great heft", closer to 100 lb/ft and required for VW Type 2 axle nuts.

It has been said that a Lanacshire good lean is in fact a bigger unit that the southern great heft, but that is a matter of dispute.

Hefts and leans do vary with time of day, post lunch is often a higher value.

[DickieG]

Excellent explanation of torque settings

[fifth_cit]

Alas I am about 25% heavier than Richards fine example, however this has to be tempered by arthritis in the shoulders preventing a good lean. I will therefore give my newly aquired torque wrench a run. (need to find more uses other than just caravan wheel nuts)
Keith

[fifth_cit]

Decided to bite the bullet and give the drop links a quick tighten up, what a difference, clunks and bangs now gone. I'll get a pair of these on order and fitted ASAP.
Thanks
Keith