Porsche Enthusiasts Club Forum

The car is back in for correction of the paint as it had started to micro blister, before taking it in I had noticed that when going over bumps I get a loud knock from the rear of the car (seems central) Also I noticed with the car stationary and increasing the rev's (approx 3k) the gear lever was starting to vibrate and vibration could also be felt through the seat base.




Does anyone think these are possibly related ?

Micro blistering in the paint means the undercoat hasn't cured off or each are incompatible. Shaking could be engine mountings, clutch cover (it has a rubber mount) or possibly the end crank bearing seal is adrift...

Dave
CT

I they are related, which I doubt, most likely suspect is a loose exhaust. Knock from the rear could be anything.
Any work done recently and something not tightened up?
Engine vibration is either belts or engine mounts if there is no misfire.
Just a couple of things related to my own experience (self inflicted and/or garage related)
I'm neurotic about such things and have been known to get up at 2 in the morning to check something that occurred to me in a dream, just to realise it was only in my dream.

Exhaust is not loose and no work done at the back recently, the engine doesn't appear to be vibrating just the gear lever and vibration through the seat

If it's from going over bumps I'd be looking at bushes before anything else....

I don't think its the bushes, I poly bushed the whole car a couple of years ago. The noise is quite central at the back and I wonder if its gear box mount ?

Yes, it could be anything that is rubber and/ or perishable....

I don't suppose your spare wheel or jack could be loose at all? That would make quite a bang over bumps.... Just a thought...

I replaced the gearbox mount last year with a semi-soild one from Lindsay Racing. Couldn't select 2nd at Knockhill hair pin. When I removed the old one it just fell apart but there wasn't a previous knock or vibration. Afterwards slight increase in perception of pinion whine but gearchange sorted.
I had I rear knock on the 993 sounded like the left side but it was the right kinematic eccentric that was loose.
On the 944 the rear knock was from torsion tube mounts, I had reused the lock nuts which didn't, new ones fitted and torqued to spec.

I'm guessing from the location you've mentioned that it's not the tailgate but on mine over bumps I was getting a knocking from the rear. On closer inspection I found that the lock wasn't engaging on one side so the tailgate could move over bumps and make a noise.

Cheers for that, I will double check the tailgate when I get the car back

wrt the "knock" from the rear, check the simple stuff first. Take out the jack and spare wheel and see if you can reproduce it. The spare wheel, in particular, can make quite a clonk over bumps if it isn't secured "just right".