Jagbuff

I guess this is one of those tough thing to explain but maybe someone on the list has experienced and can give me pointers.

When I engage first gear and start releasing the clutch and applying some throttle I regularly feel/ hear a clunk like something in the drivetrain is shifting.

Once the car gets rolling I can't tell (b/c of ambient noise) if it is doing it through the other gear shifts, and haven't notice anything on the downshifts.

The clutch doesn't slip, and the car has 28K miles.

Thought it might be a loose driveshaft but couldn't see anything abnormal.
Any suggestions?

Sachin Misra

I have a C4S with 36K miles, and I hear the same thing. I thought it was the viscous coupling but it checked out fine. My clutch has about 7K miles and doesn't slip either. I'm thinking it's something in the trans.

Let me know if you figure this out, and I'll do the same.

Martin S.

I had a clunk when engaging 1st gear....it was the dreaded dual mass failure. I replaced with a RS flywheel and clutch...clunk gone. Maybe the problem is much simpler...I hope!

deltawedge

dare I ask what is the failure mode?

viperbob

I would have to agree with Martin that it sounds from your description like the dual mass flywheel going bad. It will tend to clunk when engaging first gear. Less on subsequent gears as the car is already moving. There may also be issues in some of the other gears feeling like it is a little tough disengaging a gear when going to the next one...

slant911

Not sure if the set-up is the same, but, my previous P-car (964) had the same symptoms when the dual mass flywheel was going out. Sounds like maybe a trip to the local doctor is in order...

chris walrod

If I may ask, how many of you that have had this slight, faint, clunk while taking off from a stop, and have LSD? Does it only happen the first time after backing up? Or, every time taking off from a stop, in first gear?

In other words, does anyone here with this problem have an open diff?

I, too, feel this may be DMF related, but need another data point..

Sachin Misra

I have LSD. Mine only happens in first gear, on random occasions. I had the dealer put in a new clutch when I bought the car, but I don't think the DMF was changed.

deltawedge

I have a similar clunk but it appears to go away if I fully depress the clutch (to the floor) and wait for the input shaft to stop, then select a gear. Because of this, I assumed it was a CV joint with a bit of play but it could be the DMF. It is also intermittant in first and second. It may happen in the other gears, but I can't hear it over the other noises.

A way to isolate it would be to jack up one rear wheel (with wheels chocked, jack stand in place and park brake off, be careful, though) and with the car in 4th gear and grab the jacked wheel and try to rotate it back and forth (it shouldn't want to move). Any play in the drivetrain will make a metallic noise as it rotated back and forth. Then isolate where the noise is coming from (a hand on the axle shaft will be able to feel the noise if it is a bad CV joint). You'll need three hands, however. Repeat procedure with other rear wheel and see where it leads you. No that I mention it, I'll do this with my car and see what happens.

deltawedge

forgot to mention I have an open diff.

993C4

I had the exact same problem as you 6months ago. The answer to your problem is a worn clutch throw-out bearing aka release bearing. It's worn out and needs to be replaced. The clunk is especially noticable after reverse situation and then moving off on 1st gear.

You will need to drop the transmission and while you're at it, you might well change your clutch disc, throw-out bearing and check that your DMF is free from heat spots or play, owise you will need to change it too.

If you hear a rattling noise during idling and shut down, you DMF is toast and you will need it replaced.

My DMF was fine upon closer inspection and I only had to replace my clutch throw-out bearing and clutch disc.

deltawedge

Did you get an explanation about how a worn throw out bearing could cause the clunk?

Since you also replaced the clutch at the same time as the throw out bearing (obviously, a good choice), it may be that the problem was solved by the new clutch.

If the old clutch was not fully disengaging (worn finger springs on the pressure plate), it would cause a drag on the drivetrain (even with the clutch pedal in) because the clutch would still be partially engaged and when a gear was selected, the transmission gears would be forced to turn; thereby taking up any slack in the drivetrain. Because all slack involves metal to metal contact, it does not take much slack to cause a clunk. With the new clutch this dragging condition may have been remedied and the clunk was gone. Personally, I hate clunks as they drive me crazy until I silence them.

Jagbuff

...Sounds like the DMF may indeed be the issue.

It is intermittent. I did notice that when I am crawling in taffic disengage the clutch vs. using engine brake to slow down, when I start up again it doesn't make the noise. Does it have a catastrophic failure mode - or does the clunk just get worst progressively? It is barely noticeable at this time.