Rear Subframe Mounts or Anti-Roll Bar Bushes?

stevieb · Unread post by **stevieb** » 28 Mar 2006, 16:47

Hello all,

2.0 exec 406 has been running well just lately, no major problems to report, except a very annoying "knocking" kind of sound from the rear that's just started in the last few weeks.

It only appears at low speed, and only on uneven surfaces. It takes VERY little for it to show itself. It sounds a lot like a box floating about loose in the boot to be honest, but seems to be coming from beneath the back seat.

I've had the back end in the air, and all the usuall culprits are still sound and intact (ARB droplinks, track bars etc - all replaced less than 5,000 miles ago too). All other bushes look to be in pretty good nick, with no sign of any excessive movement when crow-barred about.

The only bushes that are almost impossible to check for movement are the ARB bushes, and the subframe mounts. The ARB bushes are in a bit of a state to look at, so I have a strong suspicion they may be the fault, but have also read on here that the subframe mounts can go - or is that only on trailing-arm'ed cars (I forget which car I read it in relation to)? Surely the multi-link nature of the suspension should avoid the mounts taking quite so much load...

I had read on the 'net that the rear seat and it's locking mechanism can cause this kind of noise, but I can't seem to replicate it by waggling the seat about, so I've dismissed that idea.

The exhaust was my other theory, especially as teh centre box took a bash the other week over a particularly nasty speed bump (it's dented the box

), but again, I can't replicate it by waggling the thing about by hand, and all the rubber mounts seem fine, with no sign that anything has been dislodged in any way.

Over to you.

rossd · Unread post by **rossd** » 29 Mar 2006, 09:47

The exhaust could have been damaged internally by the whack and something inside could be rattling??

stevieb · Unread post by **stevieb** » 30 Mar 2006, 15:59

I had wondered that Ross, but it's not a tinny kind of sound.

Imagine putting a large bolt into a tupperware box, and putting it on top of your dash. The sound the bolt makes, is the sound I'm getting from the rear. There's a very slight delay between hitting a bump and the noise, so it's definitely something loose. Not an ARB droplink, which would clonk immediately.

And it's inconsistent. I can use the same bit of road three times in a day and it doesn't always appear.

By bangint the trim in the boot, on the right hand side, I can get quite a loud rattle/clatter. I wonder if there's anything mounted behind there, that's come adrift. I'm off tomorrow, so I'll have a look.

The handling seems fine, so whatever it is, it isn't too major.

stevieb · Unread post by **stevieb** » 02 Apr 2006, 02:28

I've pulled away the RH trim in the boot, and found nothing untoward.....

I think I'll be buying new AR bushes on Monday...

I can't see it being anything else.....

stevieb · Unread post by **stevieb** » 05 Apr 2006, 18:54

Well, I changed the ARB bushes last night.

For the first 30 - 40 miles today the sound was a lot better, but then as the new bushes bedded in it returned.

I've had passengers in the rear with the unoccupied rear seat lowered, and they confirm that the sound is soming from the nearside wheelarch itself.

I had suspected that the ARB was clicking against its clamp, but that appears not to be the case now. The sound isn't a traditional "clonk". It definitely a "thud-thud-thud" in quick succession. It actually sounds like a loose panel, being disturbed by the undulations in the road - but all panels are secure.

One thing I've tried is travelling over the bumps that cause it with the handbrake slightly applied - attempting to create som drag and possible mute the sound a little, but this has no affect at all - so I'm presuming the sound is not directly related to the suspension arm and/or trailing link, or anything else that would respond to the extra drag.

So, I'm down to replacing the nearside droplink, and possible the top link (a definite possibility if the inner joint has failed).

If all that fails then I'm flumoxed.

What does a failed damper sound like? Very unlikely I know, but it's in the right area...

Any more suggestions, or things I can try to help eliminate other possibilities?

Quick edit - Now I remember how best to describe the noise - my 405 estate had the jack stored in a cubby-hole just behind the nearside wheelarch, and if it wasn't secured in there properly, it would rattle against the inner skin of the body. This sound is exactly the same.

I think I'll get some genuine ARB droplinks tomorrow and try that.

demag · Unread post by **demag** » 05 Apr 2006, 23:53

Yes I think worn shocks can sound like that.

stevieb · Unread post by **stevieb** » 08 Apr 2006, 15:28

Well, with just the nearside droplink changed, the noise has gone - completely. I'm just about to do the other side.

So, a word of warning - don't expect Motaquip ARB droplinks to last more than 7,000 miles. Use genuine parts.