New clutch knocks. Stops knocking when pedal depressed...

[rolls 912]

Hi
I have replaced all the clutch components on my 915. When warm there is a knocking sound coming from the clutch. This disappears when the pedal is depressed. What's the easiest way to fix pls?

[fred cook]

Sounds like a bad throwout bearing. Probably the only fix is going to be to replace the bearing. Did you replace the small transmission input shaft bearing that is in the end of the crankshaft? That could also be the culprit. Good luck!

[rolls 912]

It was checked by my mech and he said it was fine.... Could it be anything else?

[DRACO A5OG]

Let's prove your wrench right, spray some lube down the port on top of the tranny using a hose fitting, if the knock goes away he miss-diagnosed or did not lube enough prior to assembly.



To be certain, it needs to dropped to see if all components are in the correct order/condition.

[rolls 912]

Hey Jim
Could there be an issue with the lube dripping onto the clutch disk? Can't remember how it sits.
Cheers

[fred cook]

When you push in on the clutch pedal, the throwout bearing fork pulls on the bearing to disengage the clutch. When in a resting position, the two parts of the throwout bearing (inner race and outer race) have a small amount of freeplay between the two parts. When the clutch pedal is pressed, that play is eliminated.
If the "new" throwout bearing was out of spec or bad out of the box it could be the source of the sound. So, that is one potential source of the knocking sound. Also, when the clutch pedal is pressed, there is a small amount of play removed from between the crankshaft and the crankshaft thrust bearing. A second "change" that could involve the knock. So, suppose that there is enough movement of the crankshaft to move the flywheel/clutch assembly back a few thousandths of an inch, just enough to keep the end of a bolt or screw from contacting a web on the block? These are about the only two things that could be causing this symptom. In my humble opinion, I think your wrench messed up and does not want to have to R and R the drivetrain again at his own expense. Unfortunately, pulling the engine and tranny out again is the only way to really find out what is going on. Good luck!

[911oclock]

I have the same issue with my 86, symptoms only occur when hot. Wouldn't a bad throughout bearing show signs when cold as well?

[DRACO A5OG]

The idea is to shoot dry lube down the access port on to the T/O Bearing:



Raise the car and remove the left side wheel and you will see the port, just make sure you shoot straight down on to the T/O. use the spray straw to guide it. Maybe a pencil to practice where it will need to hit???

[rusnak]

I think it's got to come back out.

Also, the clutch disc will probably outlive the main seal and pilot bearing, in addition to the throwout bearing. In my opinion, it makes sense to change all of these at clutch disc replacment time.

[rolls 912]

Very frustrating considering I've been working on this thing for years + everything is brand new. it's in a long nose and it's a real pain to drop - squeeze.
Tell me, if I left it whats the long term repercussions?

[Two Rivers]

Delete

[john walker's workshop]

was the trans apart ever? if the 5th/reverse shift sleeve is too close to the reverse idler gear they will contact and make a rattling sound. push in the clutch and the mainshaft stops.

[wayner]

I don't know about these 911 trannys but that is a common symptom of a bad input shaft bearing inside the transmission.

If your clutch and throwout bearing are ok, you might have to look at that.

[john walker's workshop]

901 mainshaft bearings did that, but 915 bearings are supported better and it's rare.

[rolls 912]

The box was opened for new syncros and freshen but that's it. The guy that did this work has 40yrs experience working on Porsches. I've since moved on as he was very slow.

What's the ramifications if I leave it?

[john walker's workshop]

so this is the first time you have run it since the transmission work? might want to put it up on jackstands and run it while you zero in on the rattle. got a mechanic's stethoscope? a length of small hose stuck into your ear does the same thing.

[pirin911]

Hi:
Mine is the opposite. 3.2 carrera 1985. I rebuilded the motor, used the same clutch PP, disk and TOB. They were working fine (few miles on them). Installed new pilot bearing. When I depressed the pedal there is a relatively loud TAC,TAC,TAC. When released it is lower. If i started the car cold it doesn,t do it. It is after a short ride.
I took the tranny fork (the one in the plate) out to correct an oil leak and inspection of loose nuts and put it again, no issues there.
So, what do you think can be happening?
Thanks.

[larrym]

i have experinced bad NEW t/O brgs that did the same noise thing in a couple non-Pcars where the clutch came as a "kit" from an otherwise reputable FLAPS

- was brg made in China or Germany ?

.

[pirin911]

Hi:
Did you find anything about the noise?

[pirin911]

Hi:
Can I disconnect the axles from the tranny so that I can go thru all gears with the car on the floor or on stands and try to isolate the noise like John Walkers said with a rubber hose on the ears or can this be not healthy for the engine and tranny to run it like this?

Thanks in advance for your attention,
Francisco