James-NZ

Hi guys! My 944 has been going great and I'm making my way through the list of mods I want to complete, however this has just been put on hold due to a knocking sound coming from the rear.

I will describe this in detail to see if we can diagnose the issue prior to pulling the car apart, I will photo diary the process and keep this thread up to date as I make my way through the job.

I first noticed a sound from the rear about a month or 2000 miles ago, it sounded like a stone in the brake or squeal tabs on the disc pads that let you know the pads are getting low. A short time later a new sound started, this time it is a light knocking sound when going around a right hand corner while accelerating, both sounds were intermittent and while the squeal did not really concern me the knocking sound did. As often with these types of things the sound went away for a while and I continued to use the car. More recently the knocking has returned and is now present on every drive. I have now ceased using the vehicle and will investigate further.

When does it make the sound?
The knocking is only present when load is on the drive-line, under acceleration or overrun, if I depress the clutch the sound immediately stops and if I am on cruse the sound is also gone or maybe heavily reduced. It is definitely coming from the LHS rear. The knock gets faster with vehicle speed not engine speed.
The squeal is only at low speed and sounds just like brake pad squeal tabs, but after inspection the brake pads are fine. I have not yet inspected the park brake drum and pads.

Describe the knock:
It is a solid knock. I cannot feel it through the chassis. It does not affect the drive, vehicle speed or ability to select gears. It happens in all gears but as speed increases it becomes harder to hear, loudest at low speed.


My thoughts;
Initially I thought it sounded brake related, so I raised the car on stands and inspected the brakes, all fine. I then inspected the drive shafts and gearbox casing, all seemed ok. Purely a visual inspection.
It now seems that it might be CV related, or perhaps internal gearbox related. I will drop the gear oil tonight and inspect for metal filings. Depending what I find will guide me to ether removal of diff cover to inspect or removal of drive shafts for further CV inspection.


Your thoughts and advise is welcomed.

VaSteve

Loose wheel? Really.


Try this test. Find a big parking lot and turn whatever direction you hear the sound. Kill the engine and shift to neutral. See if the sound is still there.

James-NZ

Great thinking, I have checked all wheel nuts to be sure (while doing the brake inspection) you are definitely thinking along the right lines, this is the type of noise.

I have not done the parking lot test, but from the road tests I have done the noise will stop, for sure, every time I depress the clutch while the noise is happening it stops immediately. That said I will be taking it for a road test tonight to warm up the gear oil prior draining, there is a car park not far from my home so I will do this test there and report my findings.

Thanks for the thoughts.

JohnKoaWood

Muffler hitting the sway bar?

PeteL

Exhaust mounts?
CV Joints loose (The 6 bolts that hold the CV to the transmission)?
Also double check the philips head screw in the rear brake rotors. I had a clunk back there that turned out to be that.