406 Rear Suspension Clonking

[evilally]

"Top links" I hear you shout, or maybe "drop links". Not so, these are new OE parts, I've even had them off the car to double check there is no problem with them. Also recent lower rose joint bush, roll bar bushes, front and rear trailing arm bushes all round. No play in wheels at any o'clock, bearings solid. Last night I checked the inner lower arm bushes with the arm off the car, they look like new, solid.

I took a damper off the car, which I assume to be original at 200k (I've had my money's worth I suppose). It has no leaks but doesn't move in and out in an entirely smooth fashion. Some very slight play in the lower bush. Would this be a likely suspect? Would a damper cause a "clonk"?

[mark21td]

A shock bush could cause this knocking, but only if it's well worn.
Have you checked the exhaust isn't knocking on something ?

[evilally]

Thanks Mark, shock bush not that worn, but understandably not at its best after 200k. Exhaust doesn't appear to be knocking on anything. Hmmm...

[stevieb]

If the rear shocks have done 200k then I'd say they're WELL past their best. The handling improvement from fitting new rear shocks on the 406 is unbelievable.

I'd avoid KYB shocks though - I've got KYB oils on the rear and they haven't lasted long. The KYB gas shocks I fitted on the front are noisy, so I can't really recommend them either, although the handling IS good with them.

[evilally]

Well I've just ordered a pair of Bilstein B4 dampers which ECP had on sale at £38 each. I don't think this will fix the clonking but it's a pretty decent price.

[stevieb]

Well I've just ordered a pair of Bilstein B4 dampers which ECP had on sale at £38 each. I don't think this will fix the clonking but it's a pretty decent price.

That IS a good price. You really won't regret changing them and seeing the improvement . It's such an easy job too - the hardest bit being the fight with the boot carpet to reach the top mounts.

I developed a light clonk on mine last year. It turns out the steel tube through the lower bush of the RH shocker is now a loose fit on its bolt - I wasn't aware of it being loose when I fitted them, but maybe I missed it - and so I've had to tighten the nut/bolt extra tight to squeeze the wishbone against it and stop it moving. Strangely the left one isn't affected the same way, so I can only presume it was delivered this way - maybe just a tiny bit loose and has worsened over time with the hammering effect of our roads to the point I could hear it... Either way, it's put me off KYB.

[evilally]

I didn't check the metal tube at the bottom of the damper too carefully, but that would make sense. Fingers crossed the new ones fix it then.

[evilally]

ECP have just cancelled the order due to supply issues Ordering from ECP went against the grain, I've never yet managed to actually get anything delivered from them, there's always some problem

[stevieb]

ECP have just cancelled the order due to supply issues Ordering from ECP went against the grain, I've never yet managed to actually get anything delivered from them, there's always some problem

Sounds like "supply issues" means "we put the wrong price on the website and don't want to honour the sales we've made at that price". Cheeky blighters!

[lexi]

Try some shims on bolts and bushes to verify. Even self amalg tape round bolt to take up wear.

[stevieb]

Try some shims on bolts and bushes to verify. Even self amalg tape round bolt to take up wear.

Heatshrink tubing is good for taking up slack on bolts

[evilally]

Ok, I finally got new Bilsteins all round (and if I'm perfectly honest, it hasn't made a significant difference, but never mind). The clonk remains

So items I have checked:

Top links and drop links by (removed from car for examination).
Levered roll bar bushes with crow bar, no play.
Levered subframe mounts with crow bar, no play.
Bearings fine.
Lower rose joint fine.
New dampers as mentioned.
Inner suspension arm bushes (look like new).
Trailing arm bushes look fine (renewed last couple of years).
Exhaust mounts fine.
Boot completely emptied.

To me, that leaves only part 1 in this diagram:



There do appear to be bushes pressed into it, but these are not available separately Has anyone heard of these giving trouble? I might attempt to remove one for closer inspection. Any other ideas? Clonk seems to be worse at low speeds over rough ground.

[evilally]

Found it, it was the roll bar bushes I couldn't get them to move with a crow bar, but I noticed I could replicate the clonk by pushing the car side to side, so I had someone do that while I was under the car. I could see immediately that the roll bar had excessive movement. I'd replaced these already 55,000 miles ago with pattern parts, so I've shelled out for OE ones.