C4 Picasso - dull thud from rear of car

[danlat1415]

I have a dull this noise coming from the rear of my C4 Picasso when going over speed bumps.
VIN - VF7**************[VIN obfuscated, can be read by forum staff]

I've had it a while and I've recently replaced my rear shocks, springs and bump stops (60k miles) and I was hoping that would resolve it, but the noise is still there.

I've taken everything out of the boot, spare wheel and kit in case something is making the noise - but it's none of them.


Has anyone any ideas what could be causing such a noise?

It's not a rattle or a metal noise, it's more of a dull thud like I've just gone though a big pot hole.

Are there any other parts that could need replacing if they're getting old?

(I live in an area of lots of speed bumps - so the car takes more bumps than average)

[myglaren]

Have you checked the security of the exhaust hangers?

[GiveMeABreak]

I believe some C4 picasso owners have also suffered with this - the fix involves some foam on the rear axle - have a look at a few posts down here on C4 owners:

http://c4owners.org/plugins/forum/forum ... php?226932

[danlat1415]

Thanks.
The foam in rear axle seemed to be limited the the Grand Picasso as far as I could tell.
The symptoms are also different. They describe as a metallic sound or creaking (when windows are down).


I'll check out the exhaust mounts.

I was thinking of things like ball joints, control arms - that kind of thing, but I'm not sure what kind of noises they would typically make when wearing.

[danlat1415]

Have you checked the security of the exhaust hangers?

I've had a quick look under the back of the car at the exhaust and it does move around a bit.
I can't see fully where the mounts/hangers are - and I could only see one mount right at the back of the car where the exhaust ends.
The rubber mount feels really old and dry and just slides around.

It's a circle rubber mount (see photo) contained in a metal circle frame.

Are there any more mounts on the exhaust other than that one?

[myglaren]

Not a clue on the C4 but a deteriorating exhaust hanger has been known to cause similar thumps as the exhaust contacts the underbody.
Just a guess really and Marc's suggestion of failing bump stops equally valid.

[adrianruk]

Just a thought but did you have the top mounts on the rear shock absorbers checked/changed? Just had to change one on a C4 Coupe which was the source of a considerable knock. The other side was fine. Part no 514234 or similar.
Adrian

[danlat1415]

Just a thought but did you have the top mounts on the rear shock absorbers checked/changed? Just had to change one on a C4 Coupe which was the source of a considerable knock. The other side was fine. Part no 514234 or similar.
Adrian

Thanks, I'll consider that.
I don't know any part numbers for the top mounts on the rear of the C4 Picasso (B78) as it's not listed on the parts list.

[adrianruk]

Just had a look & you're right. The damper is different to the C4 coupe ones & instead of having a separate mounting (514234) it just has a "flexible bush" which will no doubt been changed with dampers.
Good luck with finding your noise!
Adrian

[danlat1415]

I've done some testing.

I've removed EVERYTHING from the back of the car, dropped the back seats and removed 2 child seats (isofix ones).
This seemed to have sorted it, so I'm happy it's not a vehicle or suspension noise, it's possibly the back seats with large high back car seats fixed in solid are not giving any flex when going over bumps, so making a dull 'solid' noise.

At least I know what I'm working with now.

Thanks for your help