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Hot!Rear suspension noise.

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sim500
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2020/06/25 23:47:27 (permalink)

Rear suspension noise.

Hi all. Noticed recently on a run out that when going over bumps/potholes a real thump from the drivers side rear. It's not the usual clonking or knocking. I can't see anything wrong and all fixing and bolts are tight. Wondered if maybe it could be the dampers worn although they are clean with no signs of leakage. Any thoughts? Car is a 996 c4s with 56k miles

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MartinTrga
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Re: Rear suspension noise. 2020/06/26 11:10:11 (permalink)
Have recently started to try to ease the thumps from the rear suspension so started with the anti-roll bar bushes.
Purchased OEM's from Porsche but bushes supplied were oversize, the bar is original, checked with the dealer the bushes supplied were correct for the vehicle, they did say there are sometimes anomalies on the system.
Porsche supplied the .26 but should have been .25
For info the part numbers are as follows:
996.333.792.24 = 18.70mm Dia
996.333.792.25 = 19.80mm 
996.333.792.26 = 20.90mm
The incorrect sized bush would have fitted in the housing and on the bar so always check the bar diameter and bush part number (moulded into the rubber).
I would also like help with updates to standard rear suspension, after 100,000 miles, is it more beneficial to change the coffin/fork arms before the dampers? I was told the springs are probably least likely to affect the ride quality? but would have thought the biggest difference would be a damper change, any thoughts?
 
wibble
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Re: Rear suspension noise. 2020/06/26 13:15:11 (permalink)
I am in the process of replacing my suspension under 'running reports'. My C4 has done over 100k with the M030 option.  With my mileage I've decided to get the suspension back to factory spec and replace all arms, whilst using coilovers. It is costly as top mounts, bolts etc all add up.
 
sim500 - It might be worth getting the car on a ramp such as an mot centre. They can check for wear and might indentify issue. The rear setup is complex with numerous bushes. At 56k my suspicion would be the shock absorber, then possibly the rear 'coffin' arm and fork. The fork may give a knock at extreme but fine for good surfaces.
 
martintrga - I thought about doing a staged upgrade as you suggest. I waited 2 years before taking the plunge, but current situation gave me the option to take the car off the road and get the suspension sorted once and for all. Changing the dampers is easier and will be less efficient at 100K. The rear coffin arms have been a complete nightmare on my rears. It is not uncommon for them to be cut out at the bolts.

Tony
1999 996 Carrera 4 - Ocean Blue
Past:
1990 944 Turbo - Guards Red
sim500
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Re: Rear suspension noise. 2020/06/26 17:48:32 (permalink)
Coffin and fork arms changed last year. I know this is a sport's car and meant to be a firm ride but I've have the car 5 years now and never noticed this thumping noise. It's very noticeable and definitely shouldn't be there. Am happy to change the dampers myself if that is the problem but wondered if anyone else has had something similar. Tyre pressures at 44psi on rears but I can't see how that could be causing it as I've always inflated to that amount. Def don't want this to get expensive. 
Richard_Hamilton
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Re: Rear suspension noise. 2020/06/27 12:46:09 (permalink)
Another possibility is the anti-roll bar drop link.  If you detach the lower joint from the ARB you can give it a tug to see if there is any play in the joints.

Richard
2017 Cayman S & Audi RSQ3
Previous:
1989 3.2 Carrera Sport, 2012 Cayman 2.9 PDK, 2006 Cayman S, 2000 996 Turbo, 1998 996 C2, 1994 993 C2
sim500
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Re: Rear suspension noise. 2020/06/29 01:52:01 (permalink)
New fitted last year. Has to be the dampers or the bush at the base of it. Thanks for the suggestion anyway Richard.
Richard_Hamilton
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Re: Rear suspension noise. 2020/06/30 08:48:46 (permalink)
Sounds like the shocker and ARB bushes are all that isn't new then!  Possibly just be the shocker top mount?  These noises are notoriously difficult to track down.

Richard
2017 Cayman S & Audi RSQ3
Previous:
1989 3.2 Carrera Sport, 2012 Cayman 2.9 PDK, 2006 Cayman S, 2000 996 Turbo, 1998 996 C2, 1994 993 C2
garrycole
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Re: Rear suspension noise. 2020/06/30 09:20:56 (permalink)
spray the top mount with a rubber friendly lubricant from underneath, worked for me.
sim500
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Re: Rear suspension noise. 2020/06/30 20:26:42 (permalink)
Thank you guys. Will try keep you updated.
MartinTrga
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Re: Rear suspension noise. 2020/07/02 09:29:44 (permalink)
Thanks would appreciate knowing what the issue was when you solve problem.
How much improvement did you notice in the ride after fitting new rear coffin/fork arms and drop links.
sim500
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Re: Rear suspension noise. 2020/07/02 20:06:38 (permalink)
Hi. It was actually just about ridding the car of annoying clonking noises when going over bumps which is a common issue it seems. As you know there are many arms and bushes but it seems it's the coffin/fork arms and drop links that are the culprits. So yes it felt and rode better but i had the geometry redone as well. Well worth doing and if you're handy with the spanners can save a few quid too. 
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