Clutch questions/info- disk, fork, shaft, bearing, etc
04-20-2014, 12:33 PM
#1
Three Wheelin'
Thread Starter
Clutch questions/info- disk, fork, shaft, bearing, etc
Hi Folks,
The "while I'm in there" projects are practically turning into a restoration. Now that the engine is out... I'm looking at the clutch.
Clutch disk:
It must have been replaced at some point prior to me taking ownership at 59k miles, though I don't have a record for it. Mileage is currently at 82k and I'm measuring the depth of the clutch surface to the tallest rivets to be a pretty consistent 0.6mm. Though that is not an easy measurement to make as the rivets aren't flat to measure against. Factory spec is 1.0mm (new) to 0.3mm (min). At just over 50% wear, I'm going to reuse this one. For the record, I measure the thickness of the full disk, measured between the rivet pairs that are closest together, as: 7.75mm (outer edge), 8.03mm (middle of surface), 8.14mm inner edge. I imagine that the difference is due to the clutch not being sandwiched between the flywheel and pressure plate for the measurement.
The disk that is in there is p/n 964.116.014.51. Looks to be superseded to 964.116.014.63. Plain old stock clutch disk.
Clutch fork:
Can anyone tell me if this is the original fork/shaft setup?
I have needle bearings in the bellhousing ears on either end of the shaft, and what appear to be steel bushings in the fork that the shaft slides into. The shaft fit is tight into the fork, but smooth and not binding. That said, it took me 3+ hours to pull the stupid shaft out using every method known to mankind. Lots of penetrating oil, heat, and tightening the M6 bolt down on a socket and washers to pull the thing out. After *a lot* of swearing, it finally started to budge. Thanks to OCD persistence.
Anyway, is this the best fork/shaft/bearing combo?
Throw out bearing:
There is a crack in the inner plastic ring on the bearing. Any guesses what can cause this? The bearing spins very freely. I remember that new ones are fairly tight and won't keep spinning on their own. I'll replace this one. But I'd like to know if this is an indication that something else is going on to have cracked the plastic. Guide tube seems fine.
Flywheel, pressure plate:
Good news is that the surfaces look excellent. The photo makes it look like it has scoring and grooving, but it's just discoloration. It is perfectly smooth and without any kind of wear that I can see. Next to check is dual mass flywheel rotation.
Clutch pedal feel:
The clutch has always felt a bit heavy, but it doesn't look like the disk is worn to the point of causing it. The needle bearings in the fork were dry. I'm wondering if that was giving it enough friction to increase the pedal resistance.
I also have always felt like the clutch could use a little more "bite". So I was surprised that the disk wasn't worn further down. Maybe a pressure plate upgrade is in order? In order of clamping force, I think this is the progression- 964 stock (1991), 964RS & stock (1992+), 993 stock, 964 3.3T. I'm not sure of the order for the 3.6T and 996GT3 plates.
The "while I'm in there" projects are practically turning into a restoration. Now that the engine is out... I'm looking at the clutch.
Clutch disk:
It must have been replaced at some point prior to me taking ownership at 59k miles, though I don't have a record for it. Mileage is currently at 82k and I'm measuring the depth of the clutch surface to the tallest rivets to be a pretty consistent 0.6mm. Though that is not an easy measurement to make as the rivets aren't flat to measure against. Factory spec is 1.0mm (new) to 0.3mm (min). At just over 50% wear, I'm going to reuse this one. For the record, I measure the thickness of the full disk, measured between the rivet pairs that are closest together, as: 7.75mm (outer edge), 8.03mm (middle of surface), 8.14mm inner edge. I imagine that the difference is due to the clutch not being sandwiched between the flywheel and pressure plate for the measurement.
The disk that is in there is p/n 964.116.014.51. Looks to be superseded to 964.116.014.63. Plain old stock clutch disk.
Clutch fork:
Can anyone tell me if this is the original fork/shaft setup?
I have needle bearings in the bellhousing ears on either end of the shaft, and what appear to be steel bushings in the fork that the shaft slides into. The shaft fit is tight into the fork, but smooth and not binding. That said, it took me 3+ hours to pull the stupid shaft out using every method known to mankind. Lots of penetrating oil, heat, and tightening the M6 bolt down on a socket and washers to pull the thing out. After *a lot* of swearing, it finally started to budge. Thanks to OCD persistence.
Anyway, is this the best fork/shaft/bearing combo?
Throw out bearing:
There is a crack in the inner plastic ring on the bearing. Any guesses what can cause this? The bearing spins very freely. I remember that new ones are fairly tight and won't keep spinning on their own. I'll replace this one. But I'd like to know if this is an indication that something else is going on to have cracked the plastic. Guide tube seems fine.
Flywheel, pressure plate:
Good news is that the surfaces look excellent. The photo makes it look like it has scoring and grooving, but it's just discoloration. It is perfectly smooth and without any kind of wear that I can see. Next to check is dual mass flywheel rotation.
Clutch pedal feel:
The clutch has always felt a bit heavy, but it doesn't look like the disk is worn to the point of causing it. The needle bearings in the fork were dry. I'm wondering if that was giving it enough friction to increase the pedal resistance.
I also have always felt like the clutch could use a little more "bite". So I was surprised that the disk wasn't worn further down. Maybe a pressure plate upgrade is in order? In order of clamping force, I think this is the progression- 964 stock (1991), 964RS & stock (1992+), 993 stock, 964 3.3T. I'm not sure of the order for the 3.6T and 996GT3 plates.
04-20-2014, 01:11 PM
#2
Technical Guru
Rennlist Member
Rennlist Member
Stiff Clutch Actuation / High Pedal Effort
04-20-2014, 02:02 PM
#3
Three Wheelin'
Thread Starter
Thanks Jason.
I would never have guessed that the TO bearing comes pre-cracked.
So the earlier fork & shaft used steel bushings in the fork and the later version used plastic? And the "upgrade" is to swap the plastic out for bronze? It sounds like the original design is the better version. Perhaps they changed to plastic because of the effort required to pull that d*mn shaft out through the steel bushings.
I could never understand why a worn clutch disk would causes a heavy pedal in these cars. Unless it was worn to the point where the pressure plate would be sitting at an angle, and for some reason that angle required more pressure. I suppose a new disk isn't out of the question at this point. I'll have to think about that.
Okay, now to pull the heads off...
I would never have guessed that the TO bearing comes pre-cracked.
So the earlier fork & shaft used steel bushings in the fork and the later version used plastic? And the "upgrade" is to swap the plastic out for bronze? It sounds like the original design is the better version. Perhaps they changed to plastic because of the effort required to pull that d*mn shaft out through the steel bushings.
I could never understand why a worn clutch disk would causes a heavy pedal in these cars. Unless it was worn to the point where the pressure plate would be sitting at an angle, and for some reason that angle required more pressure. I suppose a new disk isn't out of the question at this point. I'll have to think about that.
Okay, now to pull the heads off...
