Hey guys, I've got a knock coming from (what feels like) under my car just behind/below the drivers seat.

It only happens when I put my foot down to give a short burst of gas from stopped position or slower speeds (knock not present in reverse).
I'm not hearing anything but it feels like something solid stumps against the bottom (only once per acceleration), first I thought it might be some play in the seat rail but that's not it...

Since I've got a C4S could it be a loose drive shaft?

Thanks guys!!!

Sid.

 

wiggle your drop links to see if it is tight.

 

OK, that sounds good, I'll check that.

Oh.... Hmmmm, yeah, I know I'm going to sound like an idiot but ehhhm... what's a drop link...

 

Hey redridge, I just googled the drop link suggestion but I don't think that's it.
I've actually had this problem on my Benz and it's not the same as what I'm experiencing now.

With the worn ball joints on the drop links it was more like a "rattle" that you would hear/feel when going over rough sections of road with my C4S it's a single physical "thud" that you can feel from something solid hitting the undercarriage and only with short bursts of acceleration.

Thanks for the suggestion though!

Any other ideas?

Cheers,

sid.

 

Holy crap... 60 views and only 1 suggestion...

I thought we had the best brains in in the business on RL!
Come on guys throw something at me (no beer bottles please).

 

Motor mount? One way to spot that is the exhaust tips are different heights.

 

All right we've got a taker!

Thanks PAC, I'm gonna check it out!

Cheers,

Sid.

 

Only cure for the motor mounts is replacing. Staying off the gas isn't possible

 

I could always cut a hole in the floor and make it a Fred Flinstone car...

Had motor mounts replaced about 6 months ago.
Checked out the motor mounts suggestion though and it measures to be about the same left to right, space also looks about the same between bumper and top of tips.

OK what about a loose drive-shaft, could that not be the cause?

 

Motor mount sounds like. The new motor mounts might of came loose

 

if it is the drive shaft.... you can pull on those as well...

 

Yeah that wouldn't be the first time something that was fixed became unfixed
Had the mounts done by indy, tried queite a few of them over the years but always seem to circle back to P. dealer at $129,- p/hr

Going to P. dealer tomorrow but want to educate myself on what it could be.
I've got a good mechanic there but just want to make sure I don't end up in a situation where they pie in my boot and tell me it's raining.

So all suggestions and advise are welcome
Have any of you experienced this (knock thing) yourselves?

Thanks guys!

 

I had the same problem, also on the driver's side.

My mechanic, a former Porsche tech, said that there is some kind of plastic piece inside the rocker panel - not sure of its function, but it's not critical. Maybe manufacturing related - which breaks loose over time. It kind of bangs around in there without any clear correlation to vehicle dynamics, sounding for all the world like something loose under the car. After a time, mine got itself stuck again and stopped making the noise. He told me that in extreme cases, they've sprayed foam inside the rocker panel to isolate the piece, but there's no real fix.

 

I have also heard that in my car. comes and goes. When I hear it, I slow down and make sure that its not my wheel falling off. Once that is confirmed, I just drive.

 

Well she's fixed!!

My mechanic at the P. dealer removed the "skin" panels from the bottom of the car and 2 (rather large) crescent shaped pieces of rubber fell down...

Turns out it was the whole top section of the transmission mount!
Got a new one installed and she's like new!

The whole thing incl. test drive took less than an hour, mount cost $300,- though... but at least they had one in stock.

Thanks for your help guys!!

Cheers,

Sid.