clutch noise

[Alan L]

My SC makes a 'thock thock thock' noise when I depress the clutch pedal. The noise is coming from the pressure plate area. I guess it can only be caused by a limited number of things. It does not disappear until the clutch has load on it. And it does not occur when the engine is cold - ie on start up and first few minutes of running.
Before I pull it down to fix, some idea as to the origin would be great.
The adjustment is correct, and it occurs no matter what pedal travel ,as soon as the clutch plate disengages.
Thanks
Alan

[gregwils]

I would probably guess the pilot bearing, but if you go to the effort to open it up be sure to examine everything including the fork and put some lube on the guide tube.

[Peter Zimmermann]

Very unusual symptom. When you push the pedal to the floor you load the throw out bearing, but I don't know how it could make a cyclic noise. Is the clutch at very high mileage (over 80K miles)?

[DRACO A5OG]

To clarify, are you writing depressed = disengaged? So cluth pedal pressed down it make the noise or when at rest?

[Alan L]

Yes, high mileage.
Depressed = clutch disengaged, ie neutral, no load. Makes noise when pedal depressed, but only from the point clutch disc disengages from flywheel. Once it takes the load up, ie return pedal slightly, the noise stops.
Pilot bearing - meaning the one the nose of the input shaft locates in?
Thanks
Alan

[Peter Zimmermann]

Alan; pull it apart before something breaks. It's not worth it to try to squeeze another couple thousand miles from it. I just can't come up with the symptom cause, but I would guess that the TO Bearing is coming apart. The pilot shaft bearing is certainly a possibility, but its pretty far down on my list. Plan on a complete clutch (disc, cover & TOB), along with a new pilot shaft bearing, new TOB release fork, new crank & m/s seals, and a new clutch cable (unless it's been replaced in the last twenty or thirty thousand miles). Possible extras are a new flywheel and new TOB guide tube.

While you're in there, check/replace your oil pressure switch, thermostat o-ring, throttle lever bushings, injector sleeves/o-rings, and your engine compartment sound pad. Also, consider replacing your rear, outboard motor mounts. Obviously, many of the extras might not be necessary because I don't know your car and what's been done to it in the recent past!

[ancashion]

Originally Posted by Peter Zimmermann

Alan; pull it apart before something breaks. It's not worth it to try to squeeze another couple thousand miles from it. I just can't come up with the symptom cause, but I would guess that the TO Bearing is coming apart. The pilot shaft bearing is certainly a possibility, but its pretty far down on my list. Plan on a complete clutch (disc, cover & TOB), along with a new pilot shaft bearing, new TOB release fork, new crank & m/s seals, and a new clutch cable (unless it's been replaced in the last twenty or thirty thousand miles). Possible extras are a new flywheel and new TOB guide tube.

While you're in there, check/replace your oil pressure switch, thermostat o-ring, throttle lever bushings, injector sleeves/o-rings, and your engine compartment sound pad. Also, consider replacing your rear, outboard motor mounts. Obviously, many of the extras might not be necessary because I don't know your car and what's been done to it in the recent past!

I have a clutch job to do soon. It took me a week to compile the list of "while you're in there" things that you posted. I wished I had found this nugget of goodness when I was looking for it!

[Alan L]

Hmm, I was hoping to avoid a long list of throw outs. The clutch is working fine - but the noise suggests something not right. Has been like that for a year or two now, but I can't figure the issue. Trying to pin down the throw out bits. Had engine out couple of years ago for something else. I had a good look then, but couldn't find anything obvious. I had a new TO bearing to put in, but forgot to change it over!!
Thanks
Alan

[pirin911]

Hi Alan:

I have the same noise. Clutch was working fine. Took out the engine for a rebuild. Put the same clutch parts except a new pilot bearing. Now it has the noise. It makes the noise when the pedal is pushed to the floor. Probably the time it was stored during the rebuild and the high humidity here trashed my TO bering. Did you identified your noise source.

Francisco Soto

[Alan L]

Hi Francisco - that is my noise exactly. I tested it again the other day. As soon as the pedal goes far enough to just disengage the clutch plate, the noise appears. If I push further, it gets a bit worse. The point it just appears there is a slight drag on the clutch and enagaging 1st gear or reverse takes a while, unless you crunch it.
Are you saying your noise appeared after fitting a new pilot bearing, ad you think it is the TO bearing?
I'm happy to replace whatever it is, but don't want to chuck out a heap of bits and hope - I would be really pissed if it still did it then.
Thanks
Alan

[pirin911]

Hi Alan:
In my engine rebuild I put a new pilot bearing and greased it very well. Didn't change the clutch disc, PP and TO bearing thinking that they were working nice before the engine rebuild. So I am inclining toward a bad TO bearing. Heard the same noise on a youtube video about TO bearing noise in another car. Oh Well, engine and tranny will have to come down again to investigate. Now I need the time. Keep posting about your findings.
Thanks
Francisco

[Alan L]

So, who is going to pull their engine frst to see if the TO bearing fixes the noise? :-)
Alan

[pirin911]

Well, today got the opportunity to go under the car with a stetoscope. While my wife depressed the clutch pedal, put the stetoscope on the clutch lever (the small one with the spring were the cable attach) and the noise comes from there (bellhousing area). So I think is the TO bearing on the fork doing the noise. If you put the stetoscope on the bellhousing you can hear it but not as loud and clear as on the clutch lever. Now looking for time to remove the engine and tranny.
Francisco

[Alan L]

OK, I finally got sick of the noise and pulled the clutch out. The pics explain what I found. The diaphragm has been rubbing on the fork barrel. Took a while to figure why - since I had adjusted it so it barely disengaged the gears.
I had my clutch plate re lined a while back while I had the engine out doing other stuff. Thought i was doing the decent thing altho the clutch was OK at the time. I finally got some measurements for a new factory clutch plate, and mine was 1mm thicker. I figured that was the issue and replaced both the clutch plate and pressure plate. It feels completely different - like a hydraulic clutch. Very soft and smooth .
Worth the effort and $s I suspect. In the 10 yrs I've had it, the clutch never felt like this.
Alan

[zelrik911]

Originally Posted by Alan L

The diaphragm has been rubbing on the fork barrel. Took a while to figure why - since I had adjusted it so it barely disengaged the gears.
I had my clutch plate re lined a while back while I had the engine out doing other stuff. Thought i was doing the decent thing altho the clutch was OK at the time. I finally got some measurements for a new factory clutch plate, and mine was 1mm thicker. I figured that was the issue

Do you recall the measurements for standard Factory and your relined clutch plate?

I have seen non OEM clutch plates on eBay at 10mm thickness & wondered if there would be any problems using these?

Peter in Melbourne

[Alan L]

Factory is 8.2mm uncompressed - ie on your bench, or disengaged in the clutch. Mine was 9mm.
Alan

[Alan L]

Just saw the bottom sentence - the 10mm bit. Mine was 9+, depending where you measured it. It my well have started life as 10mm since it has been in the car for 3-4 yrs now. I had it re-lined locally - ie it was my old plate. I reassembled the trans/engine on my shop floor and looked at the gap when clutch depressed , thru the inspection hole in the bell housing. I used the tension screws in the clutch to unload the diaphragm. I had about 1 mm free clutch space when disengaged - I struggle to see how the 10mm plate would work under these conditions. You would have to over stretch the diaphragm fingers. The gap bewteen the extended diaphragm and the fork barrel is near nil. I tested this with engine blue on the diaphragm. You would be lucky to have 1mm clearance when set up optimally. Which I guess is why the set up is so important - going by the precise book measurements they give.
You can see the clearance between diaphragm/fork barrel thru the inspection hole. Have a look next time.
Regards
Alan

[zelrik911]

Originally Posted by Alan L

Just saw the bottom sentence - the 10mm bit. Mine was 9+, depending where you measured it. It my well have started life as 10mm since it has been in the car for 3-4 yrs now. I had it re-lined locally - ie it was my old plate. I reassembled the trans/engine on my shop floor and looked at the gap when clutch depressed , thru the inspection hole in the bell housing. I used the tension screws in the clutch to unload the diaphragm. I had about 1 mm free clutch space when disengaged - I struggle to see how the 10mm plate would work under these conditions. You would have to over stretch the diaphragm fingers. The gap bewteen the extended diaphragm and the fork barrel is near nil. I tested this with engine blue on the diaphragm. You would be lucky to have 1mm clearance when set up optimally. Which I guess is why the set up is so important - going by the precise book measurements they give.
You can see the clearance between diaphragm/fork barrel thru the inspection hole. Have a look next time.
Regards
Alan

Hi Alan - great that you sorted this out. Which Clutch Kit did you use that ended up feeling so good?
In your pics it looks like there is is some rubbing onto the alloy clutch fork pivots as well (or is this just because you cleaned it)?

I have a 2nd hand clutch plate that measures 7.5mm - but I must admit that I ordered the 10mm plate from eBay just BEFORE I saw your post (Murphy's Law of Porsches!!!). It hasnt arrived yet, but perhaps I can get a Clutch & Brake place to 'turn' the lining down 1.5mm for me??
Peter in Melb.

[Alan L]

The pivot points for the fork are untouched, and I hadn't cleaned it - that is how it opened up. However, I did some measurements etc. I had lost about 0.5mm off the fork barrel, and it was about 10thou away from scraping the fork pivot points you refer to. The barrel flat bit was about 10thou proud of the casting lugs.
I just used a factory plate and pressure plate - Sachs.
Peter - the 10mm plate MAY work - I guess they make them for a reason. But in my unit I'm sure it would have compounded the problem (mine may have been about 10mm when I fitted it). Turning the extra down may not work - for 2 reasons - I set mine up in my lathe to skim a bit off it too - until I saw it was not totally regular in shape - ie had a slight wobble, and depending on the linings there are clearance grooves cut in them to allow the debris to exit. It may not be wise to loose those.
What you can do is test assemble - which usually means tensioning the pressure plate with the 3 screws - which simulates having your foot on the clutch pedal. Then have a look thru the gaps in the pressure plate housing and you will see how much clearance you have. Then look thru the casing top inspection hole and you will see how far clear of the fork unit you are. You could probably measure this gap with a strip of shim plate or similar poking down the hole between the fork barrel and pressure plate. Or rotate the unit via the ring gear and then pull down and see if any rubbing. But beware - you need a bit more clearance than the cold unit on the floor needs. Mine only did this thonking noise when the engine was up to temp. From dead cold, it was as quiet as. The pressure plate probably expands. If you have a free moving friction plate (say 1mm clearance) and about 1mm (hopefully more) clearance of the fork, you may be OK.
Alan