915 Shuddering during 1st/Reverse Clutch Release

[OsoMoore]

For the past summer I have had a little roughness when releasing the clutch, but it was minimal and often I didn't notice it. I assumed my clutch was going to need replacing eventually, but only has ~60K on it.

Yesterday I went on hour drive in 85 degree weather. After the hour drive, I was stuck in stop-and-go traffic for half an hour longer. Near the end of the jam, I found a problem relatively rapidly arose.
During release of the clutch going into 1st gear, instead of a smooth transfer of power, I had a bucking motion of the entire car, as though the clutch were catching and releasing intermittently. I took great care to do as few starts and stops as possible, and thankfully soon was able to park. I had no issues shifting between gears after I was rolling: only while starting from a stop.

The car was parked for about 5 hours (at the EAA airplane convention) and when I went to leave, the issue was mostly gone. I still had some shuddering, more than normal, but not enough to make it hard to drive. I drove the hour home and it did not appear to get worse.

Today I took the car to work and the issue has remained about the same severity as the drive home yesterday.

I took a look underneath tonight, and the clutch cable has proper clearance away from the throttle cable (although there is some old wear from long ago, but not through the sheath). I checked this in both clutch up and down positions.
There is some grease spattered in the classic ring around the CV joint line. However I think this is from just before a boot replacement a few years ago. The boots looked fine tonight.
My engine and transmission mounts are only about 5 years old and appeared in good shape.

On a scale of 0=normal and 100=undrivable, I went from a standard ~5 pre-trip to a sudden 75-95 during the traffic jam. On the way home and now it is 15-20.

Any ideas on the likely culprit or means to diagnose without dropping the engine? Any chance it is actually due to grease heating and escaping from the CV joint and getting in the clutch inspection port?

I daily drive the car, but can take the boring car if it is likely to worsen or strand me. Thanks for reading!

[zedsn]

Could be with the heat build up from stop and go traffic your old disc got glazed or another possibility is your flywheel got a small warp from the heat build up. A new clutch may be in order. My 2 cents.

[cabmandone]

I think I'd start by making sure the clutch was adjusted properly.
https://www.pelicanparts.com/techarticles/101_Projects_Porsche_911/11-Clutch_Adjustment/11-Clutch_Adjustment.htm

[jlex]

Rear main seal leak getting on clutch disk causing it to grab? See any leaks?

[OsoMoore]

Originally Posted by zedsn

Could be with the heat build up from stop and go traffic your old disc got glazed or another possibility is your flywheel got a small warp from the heat build up. A new clutch may be in order. My 2 cents.

I sure hope not, but it isn't as daunting as my transmission rebuild 4 years ago. Of course, now I have a 2-year-old. If I have to drop, that will definitely be something I will check.

Originally Posted by cabmando

I think I'd start by making sure the clutch was adjusted properly.
https://www.pelicanparts.com/techarticles/101_Projects_Porsche_911/11-Clutch_Adjustment/11-Clutch_Adjustment.htm

I'll work through the adjustment again. Its been a while and something may be out of wack. The bolts were tight on the main adjustment underneath.

Originally Posted by jlex

Rear main seal leak getting on clutch disk causing it to grab? See any leaks?

I've had a very light oil drip (less than 5 drips a night) since I got the car 5 years ago, and it hasn't increased as far as I can tell. Maybe the heat caused a slow leak to increase? I'll try putting clean cardboard under it tonight to gauge if it has increased.

[30westrob]

I had the same problem on a 80 911SC. I was frustrated and thought, nothing to loose with this clutch. From a standstill I reved and dropped the clutch like it was an old muscle car. I did this 2 or 3 times until I could smell clutch. For the next 30K miles the clutch worked flawlessly without any chatter.
My only guess is by taking the clutch to a much higher than normal temp I removed oil or other contaminants.
Rob

[Walter_Middie]

Check that the nuts and bolts that hold the trans to the engine are tight. It’s happened to me twice. Symptoms just like you are describing.

[dentist90]

I’m experiencing something like you. If I rev the motor up and try to feather the clutch I can get violent bucking of the car, enough to pop it out of 1st gear. If I keep revs low and ease out he clutch not much above idle it’s all good. Shifts after I’m rolling are all just beautiful. I was thinking maybe my flywheel is warped. Possible. Or maybe there’s oil contamination on the friction disc, but it doesn’t just slip but shudders violently but only from standstill. I was wondering what effect a broken spring on a clutch disc would have? Would this produce violent bucking at takeoff?

[OsoMoore]

Originally Posted by Walter_Middie

Check that the nuts and bolts that hold the trans to the engine are tight. It’s happened to me twice. Symptoms just like you are describing.

I took a quick look at this while I was under last night. I'll take a closer look and try tightening.

[T77911S]

I have always known it as clutch chatter
its hot spots on the flywheel
they get there from how you drive it. mainly how you pull off from a stop. too much slipping the clutch will put hot spots on it.
if you ever look at a flywheel with them you will see "blue" spots on it. you may get away with block sanding it or it can be bad enough it needs to be cut.

when I got my 930 it had a little clutch chatter. I had to be careful when starting off. now it does not do it.

I had a VW when I was a kid that did it real bad, turned out both motor mounts were broken, replaced and all was good.

try not reving the engine so much and release the clutch a little quicker.

[RedCoupe]

I agree with T77911S comment about motor mounts. Engine and transmission mounts that have gone soft over time can make a tendency to have clutch chatter much worse. If the mounts are very old, I would change them. Could help a lot.

[OsoMoore]

Originally Posted by RedCoupe

I agree with T77911S comment about motor mounts. Engine and transmission mounts that have gone soft over time can make a tendency to have clutch chatter much worse. If the mounts are very old, I would change them. Could help a lot.

Engine and transmission mounts are new as of about 4 years ago. I can quickly take one off and make sure it is not solid and not squishy.

I'll try to eliminate as many things as possible before dropping the engine.

[Jonny H]

I’ll wager the clutch fork has sheared on one side.

[Walter_Middie]

I’ll wager the clutch fork has sheared on one side.

I had that one happen too. The result was the throwout bearing destroyed itself in seconds. Much different than chatter.

[jlex]

Originally Posted by OsoMoore

I've had a very light oil drip (less than 5 drips a night) since I got the car 5 years ago, and it hasn't increased as far as I can tell. Maybe the heat caused a slow leak to increase? I'll try putting clean cardboard under it tonight to gauge if it has increased.

Is that leak coming out of the bellhousing area?

[Jonny H]

Originally Posted by Walter_Middie

I had that one happen too. The result was the throwout bearing destroyed itself in seconds. Much different than chatter.

Well on mine, one side of the fork bent but did not break. The judder got worse and worse as it bent further. I was a hundred miles from home but managed to get back without it breaking. The clutch pedal felt very odd, like it need adjustment and sort of ‘squishy’.

When it was apart the bent leg was torn and hanging on by a small amount of metal.

[lrodri64]

Check the bow of the clutch cable cover. You need to increase the bow installing some washers.
That solved mine